Concentration dependent structural, thermal, and optical features of Pr3+-doped multicomponent tellurite glasses

Concentration dependent structural, thermal, and optical features of Pr3+-doped multicomponent tellurite glasses

Accepted Manuscript 3+ Concentration dependent structural, thermal, and optical features of Pr -doped multicomponent tellurite glasses G. Lakshminaray...

4MB Sizes 0 Downloads 65 Views

Accepted Manuscript 3+ Concentration dependent structural, thermal, and optical features of Pr -doped multicomponent tellurite glasses G. Lakshminarayana, Kawa M. Kaky, S.O. Baki, Song Ye, A. Lira, I.V. Kityk, M.A. Mahdi PII:

S0925-8388(16)31792-3

DOI:

10.1016/j.jallcom.2016.06.069

Reference:

JALCOM 37938

To appear in:

Journal of Alloys and Compounds

Received Date: 18 April 2016 Revised Date:

6 June 2016

Accepted Date: 8 June 2016

Please cite this article as: G. Lakshminarayana, K.M. Kaky, S.O. Baki, S. Ye, A. Lira, I.V. Kityk, M.A. 3+ Mahdi, Concentration dependent structural, thermal, and optical features of Pr -doped multicomponent tellurite glasses, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.06.069. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Graphical abstract

AC C

EP

TE D

M AN U

SC

RI PT

Raman spectra of all the synthesized glasses

ACCEPTED MANUSCRIPT

Concentration dependent structural, thermal, and optical features of Pr3+doped multicomponent tellurite glasses

SC

RI PT

G. Lakshminarayanaa,*, Kawa M. Kakya, S.O. Bakib, Song Yec, A. Lirad, I.V. Kityke, M.A. Mahdia a Wireless and Photonic Networks Research Centre, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia b Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia c School of Materials Science and Engineering, Tongji University, Shanghai 201804, China d Department of Physics, Faculty of Science, Autonomous University of Mexico State, C.P. 50000 Toluca, Mexico e Faculty of Electrical Engineering, Czestochowa University of Technology, Armii Krajowej 17, PL-42-217 Czestochowa, Poland

M AN U

Abstract

Tuning the structural, thermal, and optical properties of low phonon energy glasses such as tellurite glasses (phonon energy ~750 cm-1) with suitable rare earth dopants is a key issue in the fabrication of solid state lasers and optical amplifiers. In this work, (70-x) TeO2-10 WO3-10

TE D

ZnO-5 TiO2-5 Na2O-(x) Pr2O3 (x=1.0 to 5.0 mol %) glasses were synthesized with high optical quality and characterized using X-ray diffraction (XRD), Scanning electron microscopy and Energy dispersive X-ray analysis (SEM-EDAX), Attenuated total reflectance-Fourier transform

EP

infrared (ATR-FTIR), Raman spectroscopy, Thermo-gravimetric analysis (TGA), Differential scanning calorimetry (DSC), optical absorption and luminescence techniques. The XRD and

AC C

SEM measurements reveal the amorphous nature of all the prepared glasses and EDAX confirms all the elements present in the respective glasses. The presence of various functional groups such as stretching vibrations of Te–O bonds in the [TeO4] trigonal bi-pyramid units, symmetrical stretching or bending vibrations of Te–O–Te or O–Te–O linkages at corner sharing sites along the chains of TeO4, TeO3 and TeO3+1, stretching vibrations of W–O– and W═O bonds in WO4 tetragonal or WO6 octagonal units, vibrations of Zn–O bonds from ZnO4 groups, including nonhygroscopic nature of the glasses are confirmed by ATR-FTIR and Raman spectra, respectively. 1

ACCEPTED MANUSCRIPT

For Pr3+-doped glasses, from the DSC profiles the glass transition temperature (Tg), onset crystallization temperature (Tx), crystallization temperature (Tc), and melting temperature (Tm) are identified and the evaluated thermal stability values varied in the temperature range of 169–

RI PT

220 °C with increasing Pr3+ doping concentration. Further, the Pr3+ -doped tellurite glasses demonstrate excellent glass stability with higher criterion of Hruby’s value (HR) between 1.9 and 3.9. From the measured optical absorption spectrum, experimental oscillator strengths are

SC

calculated and used to evaluate three phenomenological Judd-Ofelt (J-O) intensity parameters Ωλ (λ=2, 4 and 6) and respective radiative properties such as radiative transition probabilities

M AN U

(AR), the branching ratios (βR), and the radiative lifetime (τR) of metastable states for 1.0 mol % Pr3+-doped glass. Five main emission transitions at 3P0 → 3H5 (530 nm; green) with a shoulder at 543 nm, a weak band at 1D2→3H4 (592 nm; orange), 3P0 → 3H6 (615 nm; orange), 3P0→3F2 (649 nm; red), and 3P0→3F3 (686 nm; red) upon exciting at 486 nm (3H4 → 3P0) wavelength are

TE D

observed from the luminescence spectra of Pr3+-doped tellurite glasses. Following the energy level diagram, Pr3+ ion concentration quenching on the luminescence intensity has been explained by a non-radiative energy transfer between the ions through cross-relaxation and

EP

energy migration processes. The concentration dependent structural, thermal, and optical behaviors of Pr 3+-doped tellurite glasses are understood and our systematic analysis could

AC C

contribute towards the development of suitable optical devices fabrication. Keywords: A: optical materials; C: optical properties; D: X-ray diffraction, thermal analysis, luminescence *Corresponding author E-mail: [email protected] Tel: +60-89466438

2

ACCEPTED MANUSCRIPT

1. Introduction Recently, rare earth (RE3+) ions doped optical glasses have drawn much attention among the

RI PT

researchers due to their potential applications in the development of switching and memory devices, superior insulators, dielectrics, Infrared (IR) lasers, IR-Visible (Vis.) converters, fiber and waveguide amplifiers for optical transmission network, and solid state lasers etc. [1–5]. In general, the optical and spectroscopic properties of rare earth ions are strongly dependent on host

SC

materials, particularly, glass hosts with low phonon energy and high thermal and glass stabilities

M AN U

are ideal for quality fiber drawing and doping rare earth (RE) ions as they reduce multiphonon de-excitations between RE ion energy levels and favor the observation of several lasing transitions with improved quantum efficiency in the near and mid-infrared regions. Among various oxide glass hosts, tellurite based glasses doped with rare earth ions have attracted much interest for optoelectronic and photonic applications due to their unique combination of

TE D

properties such as relatively high linear (n~1.8–2.3) and nonlinear (20–50 x 10-20 m2/W) refractive indices, low phonon energy (~750 cm-1), and wide transmission window in the infrared spectral range (0.4–5 µm), good chemical and mechanical stability, low glass transition and

EP

melting temperature, and higher rare earth (RE) ion solubility to fabricate glass samples at high

AC C

RE ion concentration [6–11].

Like conventional glass formers such as SiO2, B2O3, GeO2 or P2O5, in tellurite based glasses though TeO2 is the main glass former (actually a conditional glass former), it does not transform to the glassy state easily under normal conditions. So other network formers or modifier oxides are necessary [12, 13]. Addition of heavy metal oxides such as tungsten trioxide (WO3) to the TeO2 glass network enhances chemical stability and devitrification resistance [10, 11, 14, 15]. It is also known that tungsten (W) ions are capable to influence the optical properties of rare earth

3

ACCEPTED MANUSCRIPT

ions in glasses, for the main reason that these ions can exist in different valence states such as W6+, W5+and W4+, respectively. In tellurite glasses, zinc oxide (ZnO) addition could enhance the thermal stability and facilitate easy glass formation and also results in breakage of Te–O–Te

RI PT

linkages for systematic conversion of TeO4 to TeO3 structural units [10,11,16,17]. By the addition of titanium dioxide (TiO2) to tellurite glasses further increase in refractive index, decrease in thermal expansion coefficient, and expansion of the glass forming region can be

SC

achieved. Furthermore, the addition of alkali oxide such as sodium oxide (Na2O) to tellurites increases their glass forming tendency and makes ion exchange possible including the rare earth

M AN U

solubility [10, 11, 18, 19].

Among various rare earth ions, Pr3+ ion shows a number of strong optical absorption bands in the UV, visible (particularly in the 420–480 nm range) and near infrared region where suitable pumping sources are commercially available. Also, considering its rich multiple energy levels for

TE D

multichannel emissions, among the rare earth ions, Pr3+ is an attractive optical activator ion which offers the possibility of simultaneous blue, green, and red emission for visible laser actions as well as infrared (IR) emission for broad band optical amplification, and energy

EP

conversion layer for photovoltaic devices [10, 20–23]. Recently, apart from the 1.3 µm emission (Pr3+: 1G4→3H5) [24], an intense IR emission located at 1.6 µm from the Pr3+: 3F4,3→3H4

AC C

transition was also observed in selenide glasses [25], which allows these glasses as promising candidates for the U-band optical amplification. Also, Zhou et.al. [26] have reported on Praseodymium (Pr3+)-doped fluorotellurite glasses broadband photoluminescence (PL) covering a wavelength range from 1.30 to 1.67 µm under both 488 and 590 nm wavelength excitations. In order to develop new kind of optical glasses for opto-electronic applications, the knowledge of their physical features in combination with structural, thermal, and optical properties seems to be

4

ACCEPTED MANUSCRIPT

a useful tool for understanding the glasses practical applications. The present investigation is part of an in-depth research on the 70 TeO2-10 WO3-10 ZnO-5 TiO2-5 Na2O (mol %) glass system doped with rare earth ions. These tellurite based glasses doped with different rare earth ions can

RI PT

be easily prepared in a large variety of chemical compositions with high optical quality. Two studies have been published earlier in which the optical analysis of the host matrix (without changing its chemical composition) containing 1.0 mol % Er3+, 1.0 Er3+/2.0 Yb3+ (mol %), and

SC

1.0 Er3+/1.0 Tm3+/2.0 Yb3+ (mol %) [10]; and 1.0 mol % Pr3+, 1.0 mol % Nd3+, and 1.0 mol % Ni2+ [11] ions were reported. The present investigations in the paper focus at understanding the

M AN U

influence of praseodymium (Pr3+) ion concentration (which is substituted for TeO2 from 1.0 to 5.0 mol %) on the structural, thermal, and spectral characteristics of 70 TeO2-10 WO3-10 ZnO-5 TiO2-5 Na2O (mol %) glass prepared at ambient atmosphere. The effect of dopant (Pr3+) concentration on the optical and luminescence properties is analyzed following the optical

TE D

absorption spectra, photoluminescence excitation and emission spectra, energy level diagram, and cross-relaxation channels. The intensity of the optical absorption transitions are calculated by using the Judd–Ofelt (JO) theory which defines a set of three intensity parameters Ωλ (λ= 2, 4

EP

and 6) that are sensitive to the ligand environment of the RE ions. Present investigations help in identifying the suitability of these glasses as potential optical materials for visible lasers and

AC C

optical amplifiers.

2. Experimental

2.1. Materials and synthesis The conventional melt quenching technique was used to prepare the tellurite glasses doped with different Pr2O3 concentrations as well as an undoped reference (host) glass. The starting materials used in the present work were high purity TeO2 (99.995%), WO3 (99.995%), ZnO

5

ACCEPTED MANUSCRIPT

(99.99%), TiO2 (99.5%), Na2CO3 (99.5%), and Pr2O3 (99.9%). All the chemicals were purchased from Sigma‒Aldrich. The nominal compositions of the six glasses synthesized in this work are summarized in Table 1 and labelled as “a”, “b”, “c”, “d”, “e”, and “f”, respectively. All the

RI PT

chemicals are weighed in stoichiometric ratio in 20 g batch each separately, thoroughly mixed using an agate mortar and a pestle, and then each of those are collected into high purity alumina crucible and heated in an electric furnace for melting at 930 °C. The optimized melting times

SC

were ranged from 30 to 25 min. (see Table 1). The melts were stirred to achieve desirable homogeneity. The homogeneous melts were subsequently poured onto a stainless steel plate and

M AN U

then quickly pressed with another steel plate. The obtained glass disks were clear, bubble free with a diameter of 3–4 cm, a thickness of ∼0.3 cm, and good optical transparency. Host glass looks slightly yellow in colour, and the praseodymium doped tellurite based glasses appear in sight with more greenish colour as the Pr3+ ion concentration increases. The internal stress

TE D

induced in the glasses during the melt quenching was released by annealing the samples below glass transition temperature at 300 °C for 5 h in air then allowed to cool slowly to room temperature. Further, to achieve smoothness all glasses were cut to 20 mm × 20 mm × 2.0 mm

EP

size by using low speed saw machine and mechanically polished to a mirror finish using SiC/water. Finally, these glass samples were prepared in two forms: powders were characterized

AC C

by employing different structural and thermal techniques; solid form for optical analysis to understand their potential applications. 2.2. Characterization

Thickness of the glass samples was measured by screw gauge. Density is an important physical parameter to understand the degree of structural compactness of the glass network. The density of the glasses was measured using the buoyancy method based on the Archimedes principle with

6

ACCEPTED MANUSCRIPT

toluene as an immersion liquid to a precision of 0.001 g. Refractive index is another important parameter to be considered with respect to the optical features of glass. An Abbe refractometer was used to measure the refractive indices of the glasses at nd (589.3 nm) wavelength using

RI PT

sodium lamp with an error ±0.001.

Structural investigations of the prepared glasses were performed using several techniques. To determine glass quality i.e., lack of crystalline phase, the conventional X-ray Diffraction (XRD)

SC

technique was used. Measurements were performed on glass powder samples using Ital Structure APD 2000 diffractometer with CuKα (λ=1.542 Å) radiation with an applied voltage of

M AN U

40 kV and 20 mA anode current. The scan rate was 2°/min., and the scan range was between 10° and 80°. The surface morphology was monitored using FE-SEM equipment FEI-NOVA NanoSEM 230 with an acceleration voltage 5 kV, equipped with an EDX detector from EDAXAmetek that allowed semi-quantitative analysis of elements. Sample preparation was performed

TE D

by adhering glass powder samples on a carbon tape for direct observation without the requirement of any conductive coating on the surface. Types of chemical bonds in the structural units present in the synthesized glasses were determined using Fourier Transform Infrared

EP

(FTIR) spectroscopy. The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra of the glass powders were measured over the 400–4000 cm−1 range by a Perkin Elmer

AC C

Spectrum 100 FTIR spectrometer with a spectral resolution of ∼4 cm−1. The finely ground glass powder was pressed directly onto the ATR diamond crystal for the FTIR measurement. WITec’s alpha 300R is an advanced Confocal Raman Microscope that integrates a high-transmission Raman spectroscopy system and a highly sensitive confocal microscope. The Raman spectra of the glasses were obtained with a WITec alpha 300R Confocal Raman system equipped with an Nd: YAG laser (532 nm) as the excitation source. An incident power of 10 mW was typically

7

ACCEPTED MANUSCRIPT

used. The Raman spectra were recorded within the spectral range of 0–3800 cm-1 for the Raman shift, with an integration time of 5 s for each single Raman spectrum. The basic thermal properties of glasses were determined by TGA and DSC measurements.

RI PT

Thermo- gravimetric analysis and differential scanning calorimetry measurements were performed with a Mettler Toledo TGA/DSC 1 HT Integrated Thermal Gravimetric Analyzer with high purity nitrogen as a carrier gas and a flow rate of 50 mL/min. About 20-30 mg glass

SC

powders were used in an alumina pan for the measurement. The samples were heated from room temperature to 1000 ºC at a heating rate of 10 ºC/min., using Al2O3 as a reference sample. The

controlled by reaction kinetics.

M AN U

average size of all the powders was below 0.5 mm, so that the weight loss of the samples was

The room temperature optical absorption spectra of all the synthesized tellurite glasses were investigated in the 200–2500 nm spectral range using a dual-beam spectrophotometer (Hitachi

TE D

U-4100 UV–Vis–NIR), and the spectral resolution for absorption spectra measurements is 2 nm. For the Pr3+-doped glasses, the room temperature photoluminescence excitation (PLE) and photoluminescence (PL) spectra in the wavelength range 200 –700 nm with spectral resolution of

EP

1.0 nm were measured using Hitachi F-7000 fluorescence spectrophotometer equipped with a 150 W xenon lamp as the excitation source.

AC C

3. Results and discussion 3.1. Physical properties

The intrinsic characteristics of different cations present in the synthesized glasses are reported in Table 2. The rare earth ion Pr3+ (r = 0.99 Å) has the same coordination number of 6 as in the case of conditional glass former Te4+ (r = 0.97 Å) showing good compatibility in synthesizing Pr3+doped tellurite glasses with WO3, ZnO, TiO2, and Na2O additions to investigate their influence

8

ACCEPTED MANUSCRIPT

on the physical, thermal, and optical properties. For the oxygen anion (O2−) we assumed the ionic radius to be equal to 1:38 Å with a field strength of F = 1:050 (Å)–2 [27, 28]. Various physical properties of all the glasses as a function of Pr2O3 content were determined from the

RI PT

experimental data and using relevant formulae [17, 29], and are listed in Table 3. It is clearly observed that density increases monotonously when TeO2 is replaced by Pr2O3 in the glasses and this may be due to greater molar mass of Pr2O3 (329.81 g/mol) than that of TeO2 (159.6 g/mol).

SC

Generally, the refractive index (n) depends on individual ions present in the glass and polarizability of cations. In general, the refractive index of the glass increases for the highly

M AN U

polarizable cations as a result of increase in the non-bridging oxygen to bridging oxygen ratio [30]. The increase in molar volume shows that addition of Pr2O3 may expand the structure of the network in the studied glasses. In our case, the refractive index was observed to be in inversely proportional to the molar volume due to decrease of the host material TeO2 content which

TE D

possesses high polarization (Te4+ ions (1.595 Å3)) than Pr3+ ions (1.38 Å3) [31]. In general, the Eopt in amorphous systems is closely related to the energy gap between the conduction and valency bands. The amorphous materials which possess metallization criterion (M) value close to

EP

1 are generally considered to be insulators. The obtained values of metallization criterion of the synthesized glasses on the basis of refractive index is varied within the range of 0.527 − 0.536.

AC C

The increasing concentration of Pr3+ ions will increase metallization criterion of the glasses. This could be due to decreasing number of refractive indices and increasing number of energy gap. The optical basicity and electronic polarizability of the oxide species, αoxide-(II), of the synthesized glass compositions are evaluated and listed in Table 3. For all the cations present in the glass matrices; Pauling electronegativity, optical basicity moderating parameters, and optical basicity are given in Table 4. The optical basicity has been successfully used to correlate a range of

9

ACCEPTED MANUSCRIPT

properties of glass with chemical composition [27]. It is well known that optical basicity parameter (˄) defines the average electron donar power of all the oxygen atoms comprising in an oxide glass. This property can be evaluated from the glass composition. In Table 4, the basicity

RI PT

moderating parameter [γi] is evaluated using: (γi) =1.36 (Xi−0.26) where Xi is the Pauling electronegativity of the cations in the glass composition [32, 33]. The increasing number of optical basicity from 0.4255 to 0.4583 (Table 3) for the synthesized glasses indicates that the

SC

ability of oxide ions to donate electrons to surrounding cations is enhanced. 3.2. Structural analysis

M AN U

The X-ray diffraction (XRD) profiles of all the prepared glasses are shown in Fig. 1 (a). All the XRD patterns show no detectable sharp diffraction peaks that would be indicative of partial crystallization during the glasses synthesis. It was observed that the profiles show only broad peaks at 20°–35° which are characteristic of the amorphous nature of the samples. This indicates

TE D

the absence of long-range atomic arrangement and the periodicity of the three-dimensional network in the synthesized glasses. The SEM micrograph shown in Fig. 1 (b) also demonstrates the amorphous structure of the host glass matrix with the particle sizes, shapes and fracture

EP

surfaces being irregular. No crystals or clusters are identified in the host glass, which is very important for its optical applications. It is well known that the Energy dispersive X-ray analysis

AC C

(EDAX) is generally used to estimate the chemical composition of the materials. We measured the EDAX spectra of all the prepared glasses, and for example, Fig. 1 (c-e) presents the EDAX spectra of the host glass, 3.0 mol % Pr2O3, and 5.0 mol % Pr2O3-doped glasses, respectively. The measurements confirm the presence of the main constituents Te, W, Zn, Ti, Na, and O in the host glass as well as the additional presence of Pr in the Pr2O3-doped glasses. Table 5 presents the experimentally and theoretically calculated wt% of the elements present in the synthesized glasses. These results indicate that volatilization of the oxides took place during the synthesis of 10

ACCEPTED MANUSCRIPT

glasses, for example, the estimated tellurium wt% (weight percent) through EDAX is lower than the nominal tellurium wt% for each of the glasses analyzed. In order to study various functional groups present in the prepared glasses, Attenuated total

RI PT

reflection Fourier transform infrared (ATR-FTIR) spectra have been measured in the spectral range of 250 – 4000 cm-1 and is shown in Figure 2 and in inset figure. Pure tellurite glasses show an IR absorption band at 640 cm-1 which is attributed to TeO4 tetragonal pyramids [34, 35].

SC

Generally, the structure of TeO2 based glasses contains two types of basic polyhedral structural units; TeO4 trigonal bipyramid, and TeO3 trigonal pyramid. However, spectroscopically it is hard

M AN U

to determine whether a synthesized tellurite based glass is built by symmetrical TeO4 groups or asymmetrical TeO3. By analogy with the crystalline tellurites it may be expected that the addition of other network modifiers such as WO3, ZnO, and Na2O in the tellurite glass transforms part of TeO4 groups into TeO3. As shown in Fig. 2, the FTIR analysis demonstrates

TE D

that the TeO2 is main glass network former while WO3 is the glass modifier in the synthesized glasses. Table 6 presents the wave numbers for different observed vibrational modes and their corresponding assignments [14, 36, 37]. In general, infrared peaks observed at 300–375 cm-1 are

EP

attributed to the stretching vibrations of W–O–W in the WO6 units. For all the glasses, we identified a diffuse band in the range of 480–580 cm−1, due to the disordered structure and this is

AC C

considered as the vibration modes of both the TeO3 and the TeO4 entities [38]. From all the infrared spectra we observed a broad asymmetric band at 580–880 cm−1. In the spectra, the band at 608 cm-1 appears very much broader, due to their disordered structure, which causes the 670 cm−1 band to appear as a shoulder. Bands at 830–890 cm-1 correspond to the stretching vibrations of W–O–W in WO4 or WO6 units. The bands at 880–980 cm-1 are assigned to the stretching vibrations of W–O– and W═O bonds associated with WO4 and WO6 units [37]. There are no

11

ACCEPTED MANUSCRIPT

characteristic absorption bands in the range of 1000–4000 cm-1, except shallow oscillations due to interference effects in the glasses (Fig. 2, inset). The OH content in the synthesized glass systems is unidentified and also stretching mode of free Te-OH group around 3450 cm-1, and

RI PT

stretching mode of weak hydrogen bond at 3100 cm-1 are not identified [39]. Usually the OH bands play a major role in tellurite optical fiber losses in the near infrared wavelength range. The matrix of the synthesized glasses offers a highly suitable chemical environment for Pr3+, since

SC

this ion can be easily incorporated homogeneously into the glasses.

The Raman spectroscopic studies are carried out on the prepared glasses to identify the presence

M AN U

of various molecular units, and characterizing the structure around active rare-earth dopant (Pr3+); and all the synthesized glasses Raman spectra are presented in Fig. 3 (a). Raman spectra of all the studied glasses showed broad peaks and shoulders which are attributed to the disorderness of the glass structure. Therefore, Raman spectra are deconvoluted into symmetrical

TE D

Gaussian functions to find out the exact molecular vibrations. The decovoluted Raman spectra of all the glasses are presented in Fig. 3 (b-g). The identified Raman band positions from Fig. 3 (a), Fig. 3 (b-g), and their respective assignments are given in Table 7 (І), (ІІ), and (ІІІ), respectively.

EP

Formally the structure of tellurite glass is similar to that of α-TeO2 [40]. The α-TeO2 structure consists of a three dimensional network of infinite chains of TeO4 trigonal bipyramids (tbp)

AC C

linked together by shared vertices. Normally a pure TeO2 glass shows Raman bands at 400 and 700 cm-1 and the 700 cm-1 should be a broad band which extends from 550 to 800 cm-1[41], and from 550 to 850 cm-1 for TeO2–WO3 glasses in particular [37, 42]. This band shape depends on the selected glass composition. Moreover, WO3 occurs in glass network as two sites, [WO4] tetrahedral and [WO6] octahedral, and forms the thermal stability W–O bond [43]. Previously it was reported [44] that in TeO2–WO3 glasses, both oxides form a continuous network with

12

ACCEPTED MANUSCRIPT

trigonal bypiramids, O=TeO2 pyramids, and O=WO5 octahedra, forming Te–O–Te, Te–O–W and W–O–W bonds. In that work [44] the authors stated that [WO4] tetrahedral coordinations are not necessary to form the network in WO3–TeO2 glasses.

RI PT

Boson peak (BP) which is a universal anomaly of the density of states in the low frequency region is temperature dependent and its position varies from 20 to 150 cm-1 depending on the host glass’s composition. In all our studied glass compositions, the appearance of the low-

SC

frequency Boson peak (<200 cm-1) shows the presence of the glass structure. In the high frequency region (in our study ˃200 cm-1) the Raman spectral features are known to originate

M AN U

from the molecular vibrations of the molecular bonds in the prepared glasses. In general, bands at 207–269 cm-1 correspond to the M–O rotational and vibrational modes [45]. Bands identified at 318–488 cm-1 demonstrate the presence of symmetric stretching (bending) vibrations of Te– O–Te linkages between the various Te-based structural units, Zn–O bonds from ZnO4 groups and

TE D

stretching vibrations of W–O–W in the WO6 units in the studied glasses [46]. From the deconvoluted Raman spectra (Fig. 3 (b-g)), the identified bands at 604–609 cm-1 are due to antisymmetric stretching of the continuous network composed of TeO4 tbp [41]. The peaks at

EP

678–703 cm-1 correspond to the asymmetric vibrations of linkages between shorter and longer Te–O bonds (i.e. TeO3+1–O–TeO3+1). The presence of the lone pair of electrons in the tellurium

AC C

leads to the formation of short and long equatorial Te–O bonds [46]. The Raman spectral features at 758–780 cm-1 in Figure 3 correspond to the cleavage of Te–O–Te linkages, TeO3+1 (or distorted TeO4) and TeO3 trigonal pyramids structures. Peaks at ~837–864 cm-1 correspond to the stretching vibrations of W–O–W in WO4 or WO6 units or stretching vibrations of the W–O bonds either in W–O–W linkages or in O=WO5 octahedra or O=WO3 tetrahedra [14, 37]. Raman peaks at 921–932 cm-1 is due to vibrations of W–O- and/or W=O in the tetrahedral [WO4] units

13

ACCEPTED MANUSCRIPT

or octahedral [WO6] units [36]. All the Raman spectra have demonstrated a fact that the phonon energy of the synthesized glasses is varied between 760 cm-1 and 780 cm-1 (maximum variation obtained for the symmetric stretch of Te–O bonds in TeO3+1 and TeO3 units). The examination of

RI PT

the results of Raman spectral features (Fig. 3) for the present glasses under investigation demonstrates that, there is no development of the structural peaks of Pr3+ ion; which indicates the fine dispersion of Pr3+ ions in the synthesized glasses and is also a clue for the absence of cluster

SC

formation [47]. 3.3. Thermal analysis

M AN U

In order to evaluate the thermal properties of the glasses, the thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC) investigations were performed. Figure 4 (a) and (b) show the TGA and DSC profiles for all the Pr3+ ion doped glasses. It is well known that TGA is used mainly for quantification of decomposition elements, loss of water hydration in samples,

TE D

and drying studies. For all the samples there is no evidence of weight loss below 100 °C due to any evaporation of residual water molecules. From figure 4 (a) inset plot, it can be seen that a considerable weight loss in the temperature range 700 to 1000 °C was occurred for powdered

EP

samples on heat treatment. Following the TGA measurements of fig. 4 (a), the analyzed weight losses (in %) are 13.69 %, 17.61%, 11.14%, 16.72%, and 11.31 %, respectively, for 1.0, 2.0, 3.0,

AC C

4.0, and 5.0 mol % Pr3+-doped glass powders. These weight loss values are obtained directly from the TGA related software available with the equipment. All the DSC scans (fig. 4 (b) exhibit a small endothermic peak corresponding to the glass transition temperature, Tg. In all DSC profiles the onset crystallization process is marked by Tx and an exothermic peak corresponding to crystallization temperature, Tc, including an endothermic peak corresponding to melting temperature, Tm is also identified. In the case of 1.0, 2.0, and 3.0 mol % Pr3+ -doped glasses, the Tg, Tx, Tc, and Tm are very clear and their values can be determined easily, whereas 14

ACCEPTED MANUSCRIPT

for 4.0, and 5.0 mol % Pr3+ doped glasses Tx, Tc, and Tm values are not well defined and therefore some care has been taken to identify the Tx, Tc, and Tm positions. For all the Pr3+ doped glasses, the identified values of Tg, Tx, Tc, and Tm are presented in Table 8. In the present

RI PT

investigation, all of the glasses have an endothermic change, Tg between 398 and 407 °C for increasing Pr3+ concentration from 1.0 to 5.0 mol %. From Fig. 4 (b), one can see that for 1.0, 2.0, and 3.0 mol % Pr3+ doped glasses the exothermic peaks are very clear which are

SC

characterized by the crystallization of γ-TeO2 and α-TeO2 polymorphics at 585−606 °C [48–50]. The absence of clearly identifiable exothermic peaks in 4.0, and 5.0 mol % Pr3+ doped glasses

M AN U

indicate the more homogeneous formation of these glasses. For glassy materials, thermal stability (∆T) is defined as the resistance to permanent change in properties caused solely by heat and the difference between the onset crystallization temperature (Tx) and glass transition temperature (Tg), (∆T = Tx −Tg) formally used as a measure of thermal stability [49]. The thermal stability of

TE D

Pr3+ glasses has increased from 169 to 220 °C with an increase in Pr3+ ion concentration from 1.0 to 5.0 mol%. Thus the doping of Pr2O3 increases the stability of the glasses and the rigidity of the network, which is in agreement with the glasses density data as criteria of packing (Table 3). For

EP

the practical applications of rare earth doped tellurite glasses in lasers (rod fabrication) and optical amplifiers (preform extrusion and high quality fiber drawing), it is important to choose

AC C

glasses which show relatively higher values of thermal stability, (∆T ˃ 100 °C) and a low temperature interval (Tm–Tx). From table 8 one can see that 5.0 mol % Pr3+ doped glass has Tm– Tx value as low as 56 °C.

A criterion of Hruby’s value (HR) given in equation (1) has been frequently used to evaluate glass stability [51]. x  g

HR= 

m  x



(1)

15

ACCEPTED MANUSCRIPT

According to Hruby’s equation, the higher value of HR for a certain glass indicates its higher stability against crystallization on heating. The calculated HR values are listed in Table 8 for all of the Pr3+ doped glasses that possess excellent glass forming tendency and thermal stability for

RI PT

their practical applications in photonics. The enthalpy of crystallization (∆Hc) is a measure of crystallization stability and can be evaluated from integration of the crystallization peak [52]. In our study, the ∆Hc values for each Pr3+ ion doped glass are measured directly during the DSC

SC

measurement with built-in software with the equipment. The ∆Hc represents the amount of energy released during crystallization and for the synthesized glasses, with Pr3+ ion concentration

M AN U

increment from 1.0 to 5.0 mol %, the ∆Hc values decreases from 83.33 to 10.31 J.g-1. For example, a low crystallization enthalpy value of 10.31 J.g-1 for 5.0 mol % Pr3+ doped glass means the glass is in stable glassy state and has a low tendency to crystallize. The calculated Tg/Tm (in absolute temperature units) values are 0.723, 0.726, 0.700, 0.707, and 0.711,

TE D

respectively, for 1.0, 2.0, 3.0, 4.0, and 5.0 mol % Pr3+ doped glasses, and weakly obeys the classical two-third rule (Tg/Tm=2/3) [53] of relation between glass transition temperature (Tg) and melting temperature (Tm) for tellurite glasses. Further, our visual examination, absence of

EP

crystalline peaks in X-ray diffraction spectra, disorderness of the glass structure through Raman spectra, existence of glass transition temperature (Tg) and crystallization temperature (Tc) in

AC C

differential scanning calorimetry profiles, indicate that all the synthesized glasses were of amorphous in nature. 3.4. Optical analysis

It is well known that, in glasses the optical absorption properties of rare earth (RE) ion depends on surrounding environment of the RE ion in the glass matrix and interaction of RE ion with ligands. The room temperature UV–Vis–NIR optical absorption spectra of host glass, and 1.0

16

ACCEPTED MANUSCRIPT

mol % Pr3+- doped glass in the wavelength region 380–2500 nm are shown in Fig. 5. It is clear from Figure 5 that the fundamental absorption edges are not sharp which is a characteristic feature of amorphous glasses. The wavelength values corresponding to the absorption edge,

RI PT

where the intensity reaches the maximum value in optical absorption spectra are taken as cut-off wavelengths (λcut-off). Generally the absorption edge is determined by the strength of oxygen bonds in the glass forming network. It is identified that the cut-off edge of these glasses locates

SC

in the visible region close to 400 nm (Fig. 5, inset). For the host glass, no absorption bands are observed and it show transparency in both measured visible and near infrared regions. For Pr3+ -

M AN U

doped glass, the spectrum consist of nine absorption bands due to the transitions from 3H4 ground state to various excited multiplets belonging to the 4f2 configuration of Pr3+ ions. Here all transitions have occurred between 4f2–4f2 intra bands. In the visible wave- length region, a group of three bands in the violet-blue region centered at 446 nm, 470 nm, 486 nm are identified and

TE D

one isolated band at 594 nm. Five absorption bands are observed in the infrared region at 1008 nm, 1435 nm, 1534 nm, 1946 nm and 2354 nm, respectively, and among them two bands are over lapped (see Fig. 5). All these nine absorption peaks can be assigned to the following

3

EP

electronic transitions 3H4→3P2, 3H4→ (3P1+1I6), 3H4→3P0, 3H4→1D2, 3H4→1G4, 3H4→3F4, H4→3F3, 3H4→3F2, and 3H4→3H6 [54]. In all of these absorption bands, 3H4→3P2 and 3H4→3F2

AC C

transitions are hypersensitive in nature as they depend strongly on neighbouring ligands and are governed by the selection rules ∆S = 0, ∆L≤2 and ∆J≤2 [55]. Here, the absorption bands arise mainly due to the electric dipole transitions and only 3H4→1G4, 3F4,3 transitions have a negligible magnetic dipole contribution [54,55]. The observed broad bands are due to the combination of inhomogeneous broadening and unresolved Stark splitting [56]. From the 1.0 mol % Pr3+-doped glass absorption spectrum, with the values of dopant ion concentration (N), thickness of the glass

17

ACCEPTED MANUSCRIPT

(t), and wavelength of the absorption band and area, the experimental oscillator strengths (fexp) are calculated following the equation [57]

2.303mc 2 × ∫ α (ν )dν tNπe2

(2)

RI PT

f exp =

where e is the charge of the electron, m is mass of the electron, c is the velocity of light, and α(ν) is the measured absorption coefficient at a given wavenumber, ν.

SC

The Judd–Ofelt (JO) theory is widely used for the analysis of the optical spectra of rare earth ions in glasses, crystals and solutions etc.. The theoretical oscillator strengths of an f-f transition

M AN U

from the ground level (ΨJ ) to an excited level (Ψ′J ′) can be calculated using the Judd-Ofelt (JO) theory [58, 59]



8   ( + 2) = × × 3ℎ(2 + 1) 9

"#,%,&

Ω" (ᴪ() (") (ᴪ* * ) (3)

where n is the refractive index of the glass, h is the Plank constant, J is the total angular

TE D

momentum of the ground state, 2 J + 1 is the degeneracy of the ground state, ν is the energy of the transition in cm-1 and Ωλ (λ = 2, 4 and 6) are the JO intensity parameters which are (λ) 2

|| are the squared reduced matrix

EP

characteristic of the lanthanide ion-host combination. ||U

elements of the unit tensor operator of the rank λ = 2, 4 and 6 and are calculated from the

AC C

intermediate coupling approximation for the transition ΨJ →Ψ′J′. The Judd–Ofelt parameters Ω2, Ω4 and Ω6 are computed by the least squares fitting analysis of the experimental oscillator strengths and the equation which evaluates oscillator strengths theoretically, and is presented in Table 9, including the spectroscopic quality factor (SQF). The r.m.s. deviations, which are a measure of the overall quality of the fit of oscillator strengths of experimental and calculated values are also presented in Table 9. Here the r.m.s. deviations are computed using the formula 18

ACCEPTED MANUSCRIPT

+,.../

∑72#8( 2(345) − 2( ) ) 0 = (4) 9−3

RI PT

where P is the number of observed transitions. The relatively small values of these deviations confirm the validity and applicability of the Judd– Ofelt theory for the 1.0 mol % Pr3+-doped glass.

SC

For Pr3+ ion, due to small energy difference between 4f and 5d orbitals, strong 4f–5d mixing can be occurred between these orbitals [60]. But the conventional Judd–Ofelt theory assumes that in

M AN U

RE ions the energy gap between 4f and 5d orbitals is large enough and the 5d orbital does not affect the f–f transition intensities. Thus the application of J–O theory to Pr3+ ion could cause generally large deviation between the measured and calculated oscillator strengths and negative values for Ω2 parameter due to fitting of 3H4→3P2 hypersensitive transition [61]. We have calculated the J–O parameters by including and excluding the 3H4→3P2 hypersensitive transition

TE D

and found that neither the calculated oscillator strengths nor the R.M.S. deviation showed any significant improvement and do not find negative values for Ω2 parameter. From Table 9, the magnitudes of the three JO intensity parameters evaluated are increased in the

EP

order Ω2 > Ω4 > Ω6. It is well known that in optical materials, the Ω2, Ω4, Ω6 parameters provide

AC C

information about the local structure and chemical bonding between doped rare earth ions and ligand field [62, 63]. Particularly, the Ω2 parameter is an indication of the degree of asymmetry of ion sites in the vicinity of rare earth ions and covalency of metal-ligand bond. The higher the value of Ω2, the more is the asymmetry of ligand field near RE ion sites and the bond is more covalent. Further, Ω6 is inversely proportional to the covalency of Ln-O (lanthanide-oxygen) bonds which can be adjusted by the composition of the glass. Ω4 is related to the rigidity of selected host materials in which the ions are located [62, 63]. The larger value of Ω2 parameter in 19

ACCEPTED MANUSCRIPT

the 1.0 mol % Pr3+-doped glass indicates the higher degree of covalence between the Pr3+ and O2ions. Here Ω4 ⁄ Ω6 value is known as spectroscopic quality factor (χ) and generally the glass with large value of χ is more potential for lasing and stimulated emissions. The spectroscopic quality

RI PT

factor for the 1.0 mol % Pr3+-doped glass is 1.546, which is five times larger than that of χ (=0.3) of the Nd3+: YAG standard laser crystal grown by Czochralski method [64]. A comparison of J– O intensity parameters (Ω2, Ω4, Ω6), ΣΩλ and spectroscopic quality factor of 1.0 mol % Pr3+-

SC

doped glass with a number of other glass systems [65–75] is presented in Table 10.

For 1.0 mol% Pr3+-doped glass, using J–O parameters (Ωλ) that are evaluated without 3P2 level,

M AN U

the radiative properties such as predicted radiative transition probabilities (AR), the branching ratios (βR), and the radiative lifetime (τR) for different transitions due to the 3P1, 3P0, 1D2, and 1G4 emission levels to their lower lying levels are determined by applying the well known equations reported in literature [26, 66, 69] and are presented in Table 11. Here the radiative properties of

TE D

Pr3+ ions depend on network formers and modifiers of the glass. Generally, the higher values of AR indicate the stronger luminescence intensity of the transitions. Also, the magnitude of branching ratio (βR) of the luminescence transitions characterizes the lasing power of the

3

EP

potential laser transitions. Among all the energy transitions, the AR values of 3P0→3F2 and P0→3H4 transitions are larger than the others. Since the branching ratio (βR) for the 1D2→3H4 3

H5 emission transitions is above 50%, it can be considered as potential laser emission

AC C

and 1G4

transitions in the selected host matrix [57, 66, 69]. From the Pr3+: 1D2 emission state, the 1D2 3

H4 transition is possible in the visible region. The calculated radiative lifetimes (τR) follow the

trend 1G4>1D2> 3P1> 3P0 and the values are 2297 µs, 143 µs, 23 µs, and 21 µs for 1G4, 1D2, 3P1, and 3P0 levels of Pr3+ in 1.0 mol % doped glass, respectively.

20

ACCEPTED MANUSCRIPT

All the synthesized Pr3+ -doped tellurite glasses are studied using excitation and luminescence spectroscopy. To study the luminescence properties of Pr3+ doped glasses, the knowledge of excitation wavelength is very important for Pr3+ ion. The suitable excitation wavelength plays an

RI PT

important role in measuring the emission spectra of rare earth ions doped optical materials. Fig. 6 (a) presents the excitation and emission spectra of the 1.0 mol % Pr3+ doped glass. We measured the excitation spectra in the wavelength range 400–500 nm, monitoring Pr3+ emission bands at

SC

530 nm, 615 nm, and 649 nm, respectively, and we have noticed higher excitation intensity bands for 649 nm monitored emission. The excitation spectra display three well defined bands at

M AN U

449 nm (3H4→3P2), 472 nm (3H4→3P1+1I6), and 486 nm (3H4→3P0) [76], respectively. Among all these transitions, we have selected 486 nm as an excitation wavelength to record the emission spectrum in the spectral range of 500–700 nm. It is well known that the energy gaps between excited states (3P2, 3P1, and 3P0) of Pr3+ are very small and the excitation energy transfers very

TE D

fast from the 3P2 state via 3P1 states to the 3P0 state by non- radiative relaxation. Next, the 3P0 excited state is depopulated giving several radiative transitions to the lower-lying states of Pr3+. The emission spectrum of 1.0 mol % Pr3+ glass has demonstrated five main emission transitions

EP

at 3P0 → 3H5 (530 nm; green) with a shoulder at 543 nm, a weak band at 1D2→3H4 (592 nm; orange), 3P0 → 3H6 (615 nm; orange), 3P0→3F2 (649 nm; red), and 3P0→3F3 (686 nm; red) upon

AC C

exciting at 486 nm (3H4 → 3P0) wavelength [66, 77]. The emission bands of Pr3+ almost cover the entire green to red visible range of 515 to 700 nm. The intensity of 649 nm (3P0→3F2) red emission band (~10 nm full width at half maximum) is much sharper and stronger than other observed green, orange, and red emission bands. Here, it is worth mentioning that for Pr3+ ions the 649 nm emission band corresponding to 3P0→3F2 transition is a “hypersensitive transition” that mainly depends on the selected host glass polarizability and structure [78]. Fig. 6 (b) shows

21

ACCEPTED MANUSCRIPT

the comparison of the emission spectra of the 1.0 to 5.0 mol % Pr3+ -doped glasses with an excitation wavelength 486 nm. From this figure, one can see that the red emission intensity of the band at 649 nm (in that sense, all of the emission bands intensity) decreases gradually with the

RI PT

Pr3+ ion concentration increment from 2.0 to 5.0 mol %. The decrease of emission intensities could be due to the quenching of fluorescence at higher concentrations (> 1.0 mol %) of Pr3+ ions. Generally, the increase in Pr3+ ion concentration enhances the luminescence intensity due to

SC

involvement of higher number of Pr3+ ions in the fluorescence process. In our case, when the Pr3+ concentration is more than 1.0 mol % (i.e., 2.0 to 5.0 mol %), the distance between Pr3+ ions

M AN U

becomes short and the absorbed energy can be exchanged non-radiatively between neighboring Pr3+ ions favoring quenching effect and decrease the emission bands intensity. These nonradiative processes are mainly due to the energy transfer through cross-relaxation (CR). Also high rare earth ion concentrations can lead to formation of aggregated clusters in the glass

TE D

matrix. The concentration quenching might not occur until optimum concentration (in our case, 1.0. mol %) because the average distance among the Pr3+ ions is large enough that the interaction between them is very weak. As shown in Fig. 6 (b), the 1D2 emission was not observed above 1.0

1

EP

mol % Pr3+ doping and quenched faster than those of 3P0 due to the cross-relaxation between D2→1G4 and 3H4→3F4 transitions [57, 79].

AC C

Fig. 7 presents the schematic energy level diagram of Pr3+ doped tellurite glass upon 486 nm excitation and energy transfer process involved. Up on exciting at 486 nm, initially the Pr3+ ions in the ground state are excited to the higher energy state 3P0, then the 3P0 excited state transfer part of these populated ions non-radiatively to nearby 1D2 state and remaining ions radiatively to lower lying 3FJ and 3HJ states with the ejection of corresponding emissions. The ions at 1D2 state depopulates to the 3H4 state causing orange emission at 592 nm. As the interaction of Pr3+ ions

22

ACCEPTED MANUSCRIPT

with lattice phonons is responsible for the nonradiative relaxation, relatively stronger emissions from 1D2 level can be identified only in host glasses which possess higher phonon energies (> 1000 cm-1) such as borate [80], and phosphates [81] that are comparable to the energy gap

RI PT

(generally ~3800 cm-1, for our studied glasses ~3685 cm-1) between 3P0→1D2 levels. For our prepared tellurite glasses maximum phonon energy is observed at ~760–780 cm-1 (see Fig. 3). Based on the energy level scheme as shown in Fig. 7, one can notice that the energy gap between D2 and 1G4 levels matches well with the energy gap between 3H4 and 3F4, so the energy transfer

SC

1

through cross-relaxation can occur easily between neighboring Pr3+ ions. Cross relaxation

1

D2 (a) + 3H4 (b) →1G4 (a) + 3F4 (b);

1

D2 (a) + 3H4 (b) →3F4 (a) + 1G4 (b)

M AN U

channels involving 1D2 level can be expressed as:

where ‘a’ and ‘b’ represent a pair of Pr3+ ions participating in the cross-relaxation process [82].

TE D

Also for 1D2 emission the energy transfer is sensitive to the Pr3+ concentration and leads to the strong luminescence intensity dependence on the doped concentration. In Pr3+ doped glasses, for the concentration quenching of luminescence, the role of both the energy migration and cross

EP

relaxation mechanisms is still a controversial issue [21, 77, 79, 82, 83] and requires further

AC C

thorough investigations.

4. Conclusions

In summary, transparent multicomponent tellurite glasses with Pr2O3 in different concentrations (1.0 to 5.0 mol %) were prepared by employing melt quenching method in view of studying their structural, thermal, and luminescence properties systematically. Amorphous nature and constituent elements present in the synthesized glasses is confirmed by XRD, SEM-EDAX profiles, while ATR-FTIR and Raman spectral profiles reveal various functional and molecular 23

ACCEPTED MANUSCRIPT

units attributed to stretching vibrations of Te–O bonds in the [TeO4] trigonal bi-pyramid units, symmetrical stretching or bending vibrations of Te–O–Te or O–Te–O linkages at corner sharing sites along the chains of TeO4, TeO3 and TeO3+1, stretching vibrations of W–O– and W═O bonds

RI PT

in WO4 tetragonal or WO6 octagonal units, vibrations of Zn–O bonds from ZnO4 groups. From the differential scanning calorimetric (DSC) studies, Tg, Tx, Tc, and Tm values are identified for each Pr3+ -doped glass and high thermal and glass stabilities are found for the doped glasses.

SC

Following the absorption spectrum, the set of three phenomenological J-O intensity parameters Ωλ (λ=2, 4, 6) were determined for 1.0 mol % Pr3+-doped glass using J-O theory and correlated

M AN U

to the structural changes in the glass network. Utilizing these J–O parameters we have evaluated different radiative properties such as predicted radiative transition probabilities (AR), the branching ratios (βR), and the radiative lifetime (τR) of metastable states of 1.0 mol % Pr3+ doped glass. Emission transitions at 3P0 → 3H5 (530 nm; green) with a shoulder at 543 nm, a

TE D

weak band at 1D2→3H4 (592 nm; orange), 3P0 → 3H6 (615 nm; orange), 3P0→3F2 (649 nm; red), and 3P0→3F3 (686 nm; red) upon exciting at 486 nm (3H4→3P0) wavelength are observed from the luminescence spectra of Pr3+-doped glasses. Strong red emission centered at 649 nm

EP

(3P0→3F2) with a full width at half maximum of ~10 nm has been observed for 1.0 mol % Pr3+doped glass as an optimum concentration. Through studying the emission spectra, the

AC C

concentration quenching and energy transition of Pr3+ in prepared glasses have been investigated. The involvement of cross relaxation route for luminescence quenching in the visible region due to non-radiative energy transfer among Pr3+ ions is explained based on the energy level scheme. Based on the emission characteristic features, such optical glasses could be suggested as potential materials for their use in the progress of optical lasers, photonic and optoelectronic

24

ACCEPTED MANUSCRIPT

devices. Further investigations and experiments are underway in elaborating such glasses under the form of preforms for optical fibers.

RI PT

Acknowledgements The authors would like to thank Universiti Putra Malaysia (UPM), Malaysia where part of the work is supported by UPM under GP-IPB/2014/9440702 grant.

References

AC C

EP

TE D

M AN U

SC

[1]. G. Tang, X. Wen, Q. Qian, T. Zhu, W. Liu, M. Sun, X. Chen, Z. Yang, J. Alloys Compds. 664 (2016) 19–24 [2]. M. Zhang, H. Wen, H. Yu, F. Ai, H. Shao, X. Pan, M. Tang, J. Yu, L. Gai, Y. Liu, J. Alloys Compds. 672 (2016) 7–12 [3]. E. Mura, J. Lousteau, G. Scarpignato, M. Rondinelli, N. Boetti, D. Milanese, "Rare-Earth Doped Phosphate Glass Fibers," in Advanced Solid-State Lasers Congress, (Paris, France). G. Huber and P. Moulton, eds., OSA Technical Digest (online) (Optical Society of America, 2013), paper AM4A.17. [4]. F. Ondrácek, J. Jágerská, L. Salavcová, M. Míka, J. Spirková, J. Ctyroký, IEEE J. Quant. Electron. 44 (2008) 536–541 [5]. F. Steudel, S. Loos, B.Ahrens, S. Schweizer, J. Lumin. 170 (2016) 770–777 [6]. P. Babu, I.R. Martín, G. Venkataiah, V. Venkatramu, V. Lavín, C.K. Jayasankar, J. Lumin. 169 (2016) 233–237 [7]. Y. Wang, X. Zhou, J. Shen, X. Zhao, B. Wu, S. Jiang, L. Li, J. Am. Ceram. Soc. 99 (2016) 115–120 [8]. F.B. Costa, K.Yukimitu, L.A.O. Nunes, M.S. Figueiredo, L.H.C. Andrade, S.M. Lima, J.C.S. Moraes, J. Phys. Chem. Solids 88 (2016) 54–59 [9]. D. Manzani, J. L. Ferrari, F. C. Polachini, Y. Messaddeq, S. J. L. Ribeiro, J. Mater. Chem. 22 (2012) 16540–16545 [10]. G. Lakshminarayana, J. Qiu, M. G. Brik, G. A. Kumar, I. V. Kityk, J. Phys.: Condens. Matter 20 (2008) 375101/1–8 [11]. G. Lakshminarayana, H. Yang, J. Qiu, J. Alloys Compds. 475 (2009) 569–576 [12]. X. Shen, Q.H. Nie, T.F. Xu, Y. Gao, Spectrochim. Acta-A. 61 (2005) 2827–2831 [13]. A. Chagraoui, A. Tairi, K. Ajebli, H. Bensaid, J. Alloys Compds. 495 (2010) 67–71 [14]. M. Celikbilek, A. E. Ersundu, S. Aydin, J. Am. Ceram. Soc. 96 (2013) 1470–1476 [15]. A. E. Ersundu, M. Celikbilek, N. Solak, S. Aydin, J. Eur. Ceram. Soc. 31 (2010) 2775– 2781 [16]. F. F. Zhang, W. J. Zhang, J. Yuan, D. D. Chen, Q. Qian, Q. Y. Zhang, AIP Adv. 4 (2014) 047101/1–11 [17]. N. Elkhoshkhany, R. Abbas, R. El-Mallawany, A.J. Fraih, Ceram. International 40 (2014) 14477–14481 [18]. M.A. Villegas, J.M. Fernández Navarro, J. Eur. Ceram. Soc. 27 (2007) 2715–2723 [19]. K. B. Kavaklıoğlu, S. Aydin, M. Çelikbilek, A. E. Ersundu, Inter. J. Appl. Glass Sci. 6 (2015) 406–418 25

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

[20]. M. P. Belançon , J. D. Marconi, M. F. Ando, L.C. Barbosa, Opt. Mater. 36 (2014) 1020– 1026 [21]. V. Naresh, B. S. Ham, J. Alloys Compds. 664 (2016) 321–330 [22]. G. Gao, L. Wondraczek, Opt. Mater. Express 3 (2013) 633–644 [23]. O. Maalej, B. Boulard, B. Dieudonné, M. Ferrari, M. Dammak, M. Dammak, J. Lumin. 161 (2015) 198–201 [24]. S. Tanabe, C. R. Chim. 5 (2002) 815–824 [25]. Y. G. Choi, K. H. Kim, B. J. Park, J. Heo, Appl. Phys. Lett. 78 (2001) 1249–1251 [26]. B. Zhou, L. Tao, Y. H. Tsang, W. Jin, E. Y.-B. Pun, Opt. Express 20 (2012) 3803–3813 [27]. C.H. Kam, S. Buddhudu, J. Quant. Spectrosc. Radiat. Transfer 87 (2004) 325–337 [28]. Periodic Table of the elements and tables of the effective ionic radii of the elements. http://www.mrl.ucsb.edu/~seshadri/Periodic/ [29]. B. Bhatia, S. L. Meena, V. Parihar, M. Poonia, New J. Glass Ceram. 5 (2015) 44–52 [30]. S. Bhardwaj, R. Shukla, S. Sanghi, A. Agarwal, I. Pal, Int. J. Modern Eng. Res. 2 (2012) 3829–3834 [31]. V. Dimitrov, T. Komatsu, J. Uni. Chem. Technol. Metallurgy 45 (2010) 219–250 [32]. J.A. Duffy, J. Non-Cryst. Solids 297 (2002) 275–284. [33]. G. Lakshminarayana, S. Buddhudu, Spectrochim. Acta-Part A 62 (2005) 364–371 [34]. R. N. Sinclair, A. C. Wright, B. Bachra, Y.B. Dimitriev, V. V. Dimitrov, M. G. Arnaudov, J. Non-Cryst. Solids 232–234 (1998) 38–43 [35]. D. Souri, Middle-East J. Sci. Res. 5 (2010) 44–48 [36]. D. Munoz-Martín, M.A. Villegas, J. Gonzalo, J.M. Fernández-Navarro, J. Eur. Ceram. Soc. 29 (2009) 2903–2913 [37]. V.O. Sokolov, V.G. Plotnichenko, V.V. Koltashev, E.M. Dianov, J. Non-Cryst. Solids 352 (2006) 5618–5632 [38]. H. M. Oo, H. M.-Kamari, W. M. D.W.-Yusoff, Int. J. Mol. Sci. 13 (2012) 4623–4631 [39]. V. Kamalaker, G. Upender, M. Prasad, V. Chandra Mouli, Ind. J. Pure & Appl. Phys. 48 (2010) 709–715 [40]. T. Sekiya, N. Mochida, A. Ohtsuka, M. Tonokawa, J. Ceram. Soc. Jpn. 97 (1989) 1435– 1440. [41]. G. S. Murugan, T. Suzuki, Y. Ohishi, J. Appl. Phys. 100 (2006) 023107/1– 6 [42]. R.A.H. El-Mallawany, Tellurite Glasses Handbook: Physical Properties and Data, CRC Press, Boca Raton, Florida, 2002. [43]. H. Fares, I. Jlassi, H. Elhouichet, M. Férid, J. Non-Cryst. Solids 396–397 (2014) 1–7 [44]. V.O. Sokolov, V.G. Plotnichenko, E.M. Dianov, Inorg. Mater. 43 (2007) 194–213 [45]. S. Marjanovic, J. Toulouse, H. Jain, C. Sandmann, V. Dierolf, A.R. Kortan, N. Kopylov, R.G. Ahrens, J. Non-Cryst. Solids 322 (2003) 311–318 [46]. V. Sreenivasulu, G. Upender, Swapna, V. V. Priya, V. C. Mouli, M. Prasad, Physica B 454 (2014) 60–66 [47]. L.M. Fortes, L.F. Santos, M.C. Goncalves, R.M. Almeida, M. Mattarelli, M. Montagna, A. Chiasera, M. Ferrari, A. Monteil, S. Chaussedent, G.C. Righini, Opt. Mater. 29 (2007) 503– 509. [48]. A. Chagraoui, A. Chakib, A. Mandil, A. Tairi, Z. Ramzi, S. Benmokhtar, Scripta Materialia 56 (2007) 93–96 [49]. S. S. Babu, K. Jang, E. J. Cho, H. Lee, C. K. Jayasankar, J. Phys. D: Appl. Phys. 40 (2007) 5767–5774 26

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

[50]. H. A. A. Sidek, S. Rosmawati, B. Z. Azmi, A. H. Shaari, Adv. Condensed Matter Phys. 2013 (2013) 1–6 (Article ID 783207) [51]. A. Hrubý, Czechoslovak J. Phys. B 22 (1972) 1187–1193 [52]. S. Manning, (2011). “A study of tellurite glasses for electro-optic optical fibre devices”. (Ph.D thesis). Retrived from https://digital.library.adelaide.edu.au/dspace/handle/2440/71483 [53]. S. Sakka, J.D. Mackenzie, J. Non-Cryst. Solids 6 (1971) 145–162 [54]. W.T. Carnall, P.R. Fields, K. Rajnak, J. Chem. Phys. 49 (1968) 4424–4442 [55]. W.T. Carnall, P.R. Fields, B.G. Wybourne, J. Chem. Phys. 42 (1965) 3797–3806 [56]. Z. Mazurak, S. Bodyl, R. Lisiecki, J. Gabrys-Pisarska, M. Czaja, Opt. Mater. 32 (2010) 547–553 [57]. F. Zhang, Z. Bi, A. Huang, Z. Xiao, J. Lumin.160 (2015) 85–89 [58]. B.R. Judd, Phys. Rev. 127 (1962) 750–761 [59]. G.S. Ofelt, J. Chem. Phys. 37 (1962) 511–520 [60]. R.D. Peacock, Struct. Bonding 22 (1975) 83–122 [61]. R. Reisfeld, Struct. Bonding 22 (1975) 123 –175 [62]. C.K. Jörgensen, R. Reisfeld, J. Less-Common Metals 93 (1983) 107–112 [63]. R. Reisfeld, C.K. Jörgensen, Excited state phenomena in vitreous materials, Chapter 58 In Handbook on the Physics and Chemistry of Rare Earths; (Eds.: K. A. Gschneidner Jr., L. Eyring), Elsevier Science Publishers B.V., (North-Holland: Amsterdam), 9 (1987) 1–90 [64]. Y.-L. Mao, P.-Z. Deng, Y.-H. Zhang, J.-P. Guo, F.-X. Gan, Chin. Phys. Lett. 19 (2002) 1293–1295 [65]. K. Binnemans, D. Verboven, C. Gorller-Walrand, J. Lucas, N. Duhamel-Henry, J. L. Adam, J. Alloys Compds. 250 (1997) 321–325 [66]. S. Mitra, S. Jana, J. Phys. Chem. Solids 85 (2015) 245–253 [67]. D. Manzani, D. Paboeuf, S.J.L. Ribeiro, P. Goldner, F. Bretenaker, Opt. Mater. 35 (2013) 383–386 [68]. L.R. Moorthy, M. Jayasimhadri, A. Radhapathy, R.V.S.S.N. Ravikumar, Mater. Chem. Phys. 93 (2005) 455–460 [69]. J. Anjaiah, C. Laxmikanth, N. Veeraiah, P. Kistaiah, J. Lumin. 161 (2015) 147–153 [70]. P. Babu, C.K. Jayasankar, Physica B 301 (2001) 326–340 [71]. G. Ajithkumar, P.K. Gupta, G. Jose, N.V. Unnikrishnan, J. Non-Cryst. Solids 275 (2000) 93–106 [72]. K. Bhargavi, V. Sudarsan, M.G. Brik, M.S. Rao, Y. Gandhi, P.N. Rao, N. Veeraiah, J. Non-Cryst. Solids 362 (2013) 201–206 [73]. V. V. R. K. Kumar, A. K. Bhatnagar, R. Jagannathan, J. Phys. D: Appl. Phys. 34 (2001) 1563–1568 [74]. B.C. Jamalaiah, J. S. Kumar, A. M. Babu, L. R. Moorthy, K. Jang, H. S. Lee, M. J. Simhadri, J. H. Jeong, H. Choi, J. Lumin. 129 (2009) 1023–1028 [75]. I. Pal, A. Agarwal, S. Sanghi, M.P. Aggarwal, J. Alloys Compds. 509 (2011) 7625–7631 [76]. G. Lakshminarayana, H. Yang, Y. Teng, J. Qiu, J. Lumin. 129 (2009) 59–68 [77]. J. Pisarska, W. A. Pisarski, D. Dorosz, J. Dorosz, J. Lumin. 171 (2016) 138–142 [78]. V.K. Tikhomirov, S. A. Tikhomirova, J. Non-Cryst. Solids 274 (2000) 50–54 [79]. B. B.-Gwizdala, M. Reben, J. Cisowski, R. Lisiecki, W. R.-Romanowski, B. Jarzabek, Z. Mazurak, N. Nosidlak, I. Grelowska, Opt. Mater. 47 (2015) 231–236

27

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

[80]. L. Zur, J. Janek, M. Sołtys, J. Pisarska, W. A. Pisarski, J. Am. Ceram. Soc. (2016) 1–8 doi:10.1111/jace.14223 [81]. Y. Liu, J. Ren, Y. Tong, T. Wang, W. Xu, G. Chen, J. Am. Ceram. Soc. 95 (2012) 41– 44 [82]. M.V. V. Kumar, K. R. Gopal, R.R. Reddy, G.V. L. Reddy, N. S. Hussain, B.C. Jamalaiah, J. Non-Cryst. Solids 364 (2013) 20–27 [83]. M. Voda, R. Balda, M. Al-Saleh, I. Sáez de Ocáriz, M. Cano, G. Lobera, E. Macho, J. Fernández, J. Alloys Compds. 323–324 (2001) 250–254

28

ACCEPTED MANUSCRIPT

Table 1. Nominal composition of synthesized glasses (mol %) and melting time at 930 ºC Table 2. The intrinsic characteristics of the different cations present in the studied glasses Table 3. Physical parameters of synthesized glasses

RI PT

Table 4. Glass basicity properties

Table 5. EDAX analysis of the (70-x) TeO2-10 WO3-10 ZnO-5 TiO2-5 Na2O-(x) Pr2O3 (mol %) glasses

SC

Table 6. Assignments of observed FTIR bands for the prepared glasses

assignments for the synthesized glasses

M AN U

Table 7. Identified Raman bands from (І) Fig. 3 (a), (ІІ) Fig. 3 (b-g), and (ІІІ) Raman bands

Table 8. Thermal properties of Pr3+ ion doped glasses

Table 9. Absorption band assignments (from the ground state, 3H4), energy (cm-1), experimental (fexp) and calculated (fcal) oscillator strengths (× 10-6) of 1.0 mol % Pr3+ -doped glass along with

TE D

J‒O parameters. Wavelengths correspond to average transition energies Table 10. Judd–Ofelt intensity parameters (Ωλ, × 10-20 cm2), ΣΩλ, and spectroscopic quality factor (χ) of Pr3+ -doped different glass systems

EP

Table 11. Emission transitions (SLJ → S′ L′J′), wavelength (nm), predicted radiative transition probabilities (AR, s-1), branching ratios (βR) and radiative decay times (τR, µs) of some

AC C

important luminescent levels of 1.0 mol % Pr3+ -doped glass

29

ACCEPTED MANUSCRIPT

Figure Captions Fig. 1. (a) X-ray diffraction (XRD) profiles of the prepared glasses (b) SEM micrograph of the host glass, and EDAX spectra of the (c) host glass, (d) 3.0 mol % Pr3+, and (e) 5.0 mol % Pr3+ -

RI PT

doped glasses

Fig. 2. ATR-FTIR spectra of all the synthesized glasses (inset, IR spectra from 1000–4000 cm-1 wavenumber)

SC

Fig. 3. (a) Raman spectra of all the prepared glasses and (b-g) Corresponding deconvoluted Raman spectra

M AN U

Fig. 4. (a) Thermo-gravimetric analysis (TGA) (inset, from 700 to 1000 °C), and (b) Differential scanning calorimetry (DSC) profiles of the Pr3+ -doped glasses

Fig. 5. Optical absorption spectra of the host glass and 1.0 mol % Pr3+-doped glass in the wavelength region 380–2500 nm, (inset, Cut-off wavelengths spectra for host, and 1.0 mol %

TE D

Pr3+ -doped glass)

Fig. 6. (a) Excitation and emission spectra of 1.0 mol % Pr3+ -doped glass (b) Emission spectra of all of the Pr3+ doped glasses with λex.= 486 nm

EP

Fig. 7. Schematic energy level diagram of Pr3+ in tellurite glass upon 486 nm excitation and energy transfer processes involved including cross relaxation process [1D2, 3H4] → [1G4, 3F4] for

AC C

Pr3+ ions

30

ACCEPTED MANUSCRIPT

Table 1. Nominal composition of synthesized glasses (mol %) and melting time at 930 ºC TeO2

WO3

ZnO

TiO2

Na2O

Pr2O3

Melting time (min.)

a

70.0

10.0

10.0

5.0

5.0

0.0

30

b

69.0

10.0

10.0

5.0

5.0

1.0

30

c

68.0

10.0

10.0

5.0

5.0

2.0

30

d

67.0

10.0

10.0

5.0

5.0

3.0

30

e

66.0

10.0

10.0

5.0

5.0

4.0

25

f

65.0

10.0

10.0

5.0

5.0

SC

RI PT

Sample code

AC C

EP

TE D

M AN U

5.0

31

25

ACCEPTED MANUSCRIPT

Table 2. The intrinsic characteristics of the different cations present in the studied glasses W4+,W5+,W6+

Zn2+

Conditional Glass glass former/Glass former/Glass modifier/Glass Intermediate Intermediate

Glass modifier

3, 4, 6

4, 5, 6

4,5,6,8

Cation oxidation number, (Z)

4, 6

4, 5, 6

2

Ionic radius, r (Å)

0.66 (C.N.= 4, 4+ charge); 0.97 (C.N.=6, 4+ charge); 0.43 (C.N.= 4, 6+ charge); 0.56 (C.N.=6, 6+ charge)

0.66 (C.N.= 6, 4+ charge); 0.62 (C.N.=6, 5+ charge); 0.42 (C.N.=4, 6+ charge); 0.60 (C.N.= 6, 6+ charge)

Field Strength, F= Z/r2 (Å)2

9.1827 for 0.66 (C.N.= 4, 4+ charge); 4.2512 for 0.97 (C.N.=6, 4+ charge); 32.450 for 0.43 (C.N.= 4, 6+ charge); 19.1326 for 0.56 (C.N.=6, 6+ charge)

9.1827 for 0.66 (C.N.= 6, 4+ charge); 13.0073 for 0.62 (C.N.=6, 5+ charge); 34.0136 for 0.42 (C.N.=4, 6+ charge); 16.6667 for 0.60 (C.N.= 6, 6+ charge)

Pr3+

4

6

1

3

0.60 0.86 (C.N.= 6, (C.N.= 4, 2+ charge); + 2 charge); 0.67 (C.N.=6, 0.68 3+ charge); 0.42 (C.N.=4, (C.N.=5, + 4+ charge); 2 charge); 0.74(C.N.= 0.605 (C.N.= 6, 2+ 6, 4+ charge) charge); 0.90 (C.N.= 8, 2+ charge)

0.99

0.99

5.5555 for 2.7042 for 0.60 0.86 (C.N.= 6, (C.N.= 4, 2+ charge); + 2 charge); 6.683 for 0.67 4.3252 for (C.N.=6, 3+ 0.68 charge); (C.N.=5, 22.6757 for 2+ charge); 0.42 (C.N.=4, 3.6523 for 4+ charge); 0.74(C.N.= 10.9290 for 6, 2+ 0.605 (C.N.= charge); 6, 4+ charge) 2.4691 for 0.90 (C.N.= 8, 2+ charge)

1.02

3.06

TE D

EP

AC C

Na+

Glass former/ Glass Dopant Glass modifier ion modifier/Glass Intermediate 4,5,6,8

2,3,4

M AN U

Coordination Number, (C.N.)

Ti2+, Ti3+, Ti4+

RI PT

Structural role

Te4+, Te6+

SC

Cations

32

ACCEPTED MANUSCRIPT

Table 3. Physical parameters of synthesized glasses Concentration of Pr2O3 (mol %)

Average Molecular Weight,

0.0

1.0

2.0

150.136

151.840

153.542

M (g/mol) 0.3

0.3

0.3

3

Density, ρ (g/cm )

5.397

5.409

5.422

Refractive index,

1.921

1.916

1.911

Dielectric constant, ɛ

3.690

3.671

3.652

Optical dielectric constant,

2.690

M AN U

nD (589.3 nm)

4.0

5.0

155.244

156.946

158.648

0.3

0.3

0.3

5.434

5.446

5.458

1.907

1.902

1.897

3.637

3.618

3.599

SC

Thickness of the glass, d (cm)

3.0

RI PT

Property

2.671

2.652

2.637

2.618

2.599

28.0717

28.3183

28.569

28.8186

29.067

69.82

69.57

69.30

69.05

68.81

13.221

13.287

13.365

13.429

13.493

0.527

0.529

0.531

0.532

0.534

0.536

5.56

5.60

5.64

5.66

5.70

5.74

………

0.2145

0.4254

0.6325

0.836

1.036

9.941

9.868

9.794

9.735

9.661

9.587

5.21

5.23

5.26

5.29

5.32

5.34

Polaron radius, (rp) (Å)

………

6.73

5.36

4.69

4.28

3.98

Interionic distance, ri (Å)

………

16.705

13.296

11.649

10.615

9.883

Field Strength,

………

6.62

10.44

13.64

16.38

18.94

Glass optical basicity, (˄)

0.4255

0.4322

0.4388

0.4453

0.4518

0.4583

Glass oxide species, αoxide(-ІІ) Å3 = 1.018 + (0.567) ˄glass + (0.783) ˄2glass

1.4010

1.4093

1.4176

1.4257

1.4340

1.4423

;

<= <;

Molar volume, Vm (cm3/mol)

27.8184 70.10

Molar Refractivity, Rm (cm-3)

13.151

Metallization criterion, M Energy gap, (Eg) (eV) NPr3+ ( x 1021 ions/cm3) Reflection loss, RL (%) Molar Polarizability, -24

AC C

3

EP

Ion concentration,

TE D

Oxygen packing density, OPD (mol/l)

αm (cm x 10 )

-2

14

F (cm x 10 )

33

ACCEPTED MANUSCRIPT

Table 4. Glass basicity properties >[email protected]

(˄) = [γi]-1

Cation

Pauling electronegativity (Xi)

Basicity moderating parameter [γ]

Te

2.1

2.5024

0.4054

0.3996

W

2.36

2.856

0.3554

0.3501

Zn

1.65

1.8904

0.5357

0.5290

Ti

1.54

1.7408

0.5814

0.5744

Na

0.93

0.9112

1.1029

1.0974

Pr

1.13

1.1832

0.8523

0.8452

A2>.@

AC C

EP

TE D

M AN U

SC

RI PT

(˄) =

34

ACCEPTED MANUSCRIPT

Table 5. EDAX analysis of the (70-x) TeO2-10 WO3-10 ZnO-5 TiO2-5 Na2O-(x) Pr2O3 (mol %) glasses Nominal composition (wt %)

EDAX composition (wt %)

Te

W

Zn

Ti

Na

O

Pr

Te (L)

W (M)

Zn (K)

Ti (K)

Na (K)

O (K)

0.0

59.50

12.24

4.35

1.60

1.53

20.78

0.0

51.92

12.18

3.23

1.25

1.28

30.14

0.0

1.0

57.99

12.11

4.30

1.58

1.51

20.65

1.86

50.70

12.06

3.47

1.17

1.20

29.65

1.75

2.0

56.51

11.97

4.26

1.56

1.50

20.53

3.67

50.38

12.11

3.55

1.30

1.22

28.84

2.60

3.0

55.07

11.84

4.21

1.54

1.48

20.41

5.45

49.33

11.73

3.36

1.21

1.45

28.33

4.59

4.0

53.66

11.71

4.16

1.52

1.46

20.29

7.19

49.06

11.64

3.27

1.29

1.41

27.13

6.20

5.0

52.28

11.59

4.12

1.50

1.45

20.17

8.88

48.27

11.56

3.33

1.05

1.25

26.78

7.76

AC C

EP

TE D

M AN U

SC

RI PT

(x) (mol %)

35

Pr (L)

ACCEPTED MANUSCRIPT

Table 6. Assignments of observed FTIR bands for the prepared glasses Wavenumber (cm-1)

Assignment Stretching vibrations of W–O–W in the WO6 units

608

Stretching vibrations of the TeO4 triagonal bi-pyramid structure

670

Stretching vibrations of Te–O bonds in the [TeO4] trigonal bi-pyramid units

855

Stretching vibrations of W–O–W in WO4 or WO6 units

939

Stretching vibrations of W–O– and W═O bonds in WO4 tetragonal or WO6 octagonal units

AC C

EP

TE D

M AN U

SC

RI PT

334

36

ACCEPTED MANUSCRIPT

Table 7. Identified Raman bands from (І) Fig. 3 (a), (ІІ) Fig. 3 (b-g), and (ІІІ) Raman bands assignments for the synthesized glasses

RI PT

(І) Raman spectral band regions Sample code

(560–880) cm-1

(880–980) cm-1

a

222,269,318,342,379,428,456

688,765

932

b

266,372,452

679,765

930

c

266,372,424,451

679,761

926

d

222,355,449

681,760

926

e

212,336,365,449,483

678,762

925

f

207,259,318,358,452,488

678,703,758,780

921

code

Raman spectral band regions

TE D

Sample

M AN U

(ІІ)

SC

(194–525) cm-1

(194–525) cm-1

(560–880) cm-1

(880– 980) cm-1

214.8,276.2,318.5,341.9,383.9,421.04,453.4,494.9

604.4,672.2,770.68,859.2

933.7

b

224.2,266.8,337.2,374.6,434.9,453.4,481.1

609.0,667.7,766.2,859.2

925.0

c

214.8,266.8,318.5,341.9,379.2,430.3,454.4,481.1

604.4,667.7,766.2,859.2

929.4

d

224.2,266.7,318.5,360.6,425.7,453.4,476.5

609.0, 667.7,766.2,859.2

925.0

e

214.8,271.5,313.8,337.2,369.9,421.0,458.0,481.1,499.5 604.4,663.2,761.7,863.6

925.0

f

205.3,229.0,262.1,313.8,360.6,439.6,453.4,494.9

AC C

EP

a

37

604.4,649.7,703.7,743.9,784.0,837.2 920.6

ACCEPTED MANUSCRIPT

(ІІІ) Wavenumber (cm-1)

Assignment Metal–Oxygen rotational and vibrational modes

318–488

Symmetrical stretching or bending vibrations of Te–O–Te or O–Te– O linkages at corner sharing sites along the chains of TeO4, TeO3 and TeO3+1 and vibrations of Zn–O bonds from ZnO4 groups; Stretching vibrations of W–O–W in the WO6 units

604–609

Anti-symmetric stretching of continuous networks of TeO4 subunits

678–703

Antisymmetric vibrations of Te–O–Te linkages constructed by two unequaivalent Te–O bonds

758–780

Cleavage of Te-O-Te linkages and stretching vibrations of Te–O bonds containing NBO in TeO3 trigonal pyramid (tp) and TeO3+1 polyhedra.

837–864

Stretching vibrations of W–O–W in WO4 or WO6 structural units

921–932

The stretching vibrations of W–O- and/or W=O in the WO4 and WO6 units and polarized totally symmetrical valent vibration of W–O bonds

AC C

EP

TE D

M AN U

SC

RI PT

207–269

38

ACCEPTED MANUSCRIPT

Table 8. Thermal properties of Pr3+ ion doped glasses (Tm–Tx) (°C)

585

655

169

88

574

586

652

175

78

400

589

606

688

189

99

e

402

609

624

682

207

73

f

407

627

640

683

220

56

b

398

567

c

399

d

HR= ∆Hc Tg Tm Cx − Cg -1 B D (J.g ) (±0.5) (±0.5) Cm − Cx (K) (K)

AC C

EP

TE D

M AN U

Tx Tc (±0.5) (±0.5) (°C) (°C)

RI PT

∆T = (Tx–Tg) (°C)

Tg (±0.5) (°C)

39

1.920

83.33

671

928

2.243

57.16

672

925

1.909

31.75

673

961

2.836

11.98

675

955

3.928

10.31

680

956

SC

Tm (±0.5) (°C)

Sample code

ACCEPTED MANUSCRIPT

Table 9. Absorption band assignments (from the ground state, 3H4), energy (cm-1), experimental (fexp) and calculated (fcal) oscillator strengths (× 10-6) of 1.0 mol % Pr3+ -doped glass along with

Levels

Wavelength (nm)

Oscillator strengths

Energy -1

(cm ) With 3P2 level

H6

2354

4249

0.043

3

F2

1946

5139

12.941

3

F3

1534

6519

16.343

3

F4

1435

6969

2.890

1

G4

1008

9921

0.763

1

D2

594

16835

3

P0

486

20576

3

P1

470

21277

3

P2

446

22422

Ω2 Ω4 Ω6

Spectroscopic quality factor (χ)

fexp.(×10-6)

0.000

fcal.(×10-6)

Residuals (×10-6)

0.043

0.043

0.000

0.049

12.941

12.892

0.049

16.281

0.062

16.343

16.281

0.062

2.880

0.010

2.890

2.880

0.010

0.760

0.003

0.763

0.760

0.003

5.216

5.196

0.020

5.216

5.196

0.020

2.568

2.558

0.010

2.568

2.558

0.010

2.387

2.378

0.009

2.387

2.378

0.009

11.956

11.911

0.045

-

-

-

TE D

12.892

EP

AC C

J‒O parameters (10-20 cm2)

0.043

Residuals (×10-6)

M AN U

3

fcal.(×10-6)

Without 3P2 level

SC

fexp.(×10-6)

r.m.s. deviation (×10-6)

RI PT

J‒O parameters. Wavelengths correspond to average transition energies

0.03

0.04

42.74 ± 0.11

42.81 ± 0.12

36.39 ± 0.14

36.69 ± 0.15

24.50 ± 8.15

23.73 ± 7.49

1.485

1.546

40

ACCEPTED MANUSCRIPT

Table 10. Judd–Ofelt intensity parameters (Ωλ, × 10-20 cm2), ΣΩλ, and spectroscopic quality factor (χ) of Pr3+ -doped different glass systems Ω2

Ω4

Ω6

ΣΩλ

TeO2-WO3-ZnO-TiO2-Na2O

42.81

36.69

23.73

103.23

1.546

Present work

ZBLAN

0.94

6.540

3.840

11.320

1.703

[65]

PbO-P2O5

0.338

6.676

5.914

12.928

1.129

[66]

IZSB5

0.7

5.3

5.0

11.0

1.06

[67]

NaTFP

0.268

7.452

5.781

13.501

1.289

[68]

CdBPr

1.32

2.27

2.78

6.37

0.816

[69]

Lithium fluoroborate

1.17

3.83

4.58

9.58

0.836

[70]

Glass A

0.25

7.47

5.37

13.090

1.391

[71]

PbO-Al2O3-SiO2

0.707

1.333

5.153

7.193

0.259

[72]

LTFPr

3.11

3.92

7.89

14.92

0.497

[73]

M AN U

SC

RI PT

Reference

2.54

4.23

9.19

0.60

[74]

2.89

2.04

1.99

6.92

1.025

[75]

EP

ZBP3

χ (Ω4⁄ Ω6)

2.42

AC C

LBTAF

TE D

Host

41

ACCEPTED MANUSCRIPT

Table 11. Emission transitions (SLJ → S′ L′J′), wavelength (nm), predicted radiative transition probabilities (AR, s-1), branching ratios (βR) and radiative decay times (τR, µs) of some

Initial state

Final state

(SLJ)

(S′L′J′)

470

7843

0.18

3

H5

530

10915

0.25

3

H6

592

1838

F2

620

3

F3

678

3

F4

699

1

G4

1

D2

3

H4

3

H6

1

D2

23

0.04

M AN U

3

τR(µs)

SC

H4

6260

0.14

13125

0.30

3952

0.09

881

419

<0.01

2252

36

<0.01

486

21181

0.45

615

2865

0.06

TE D

P0

βR

3

3

F2

649

17830

0.38

3

F4

735

4338

0.09

1

G4

939

730

0.02

1

D2

2673

12

<0.01

3

H4

594

4556

0.65

AC C

3

P1

AR(s-1)

EP

3

Wavelength (nm)

RI PT

important luminescent levels of 1.0 mol % Pr3+ -doped glass

42

21

143

686

20

<0.01

3

H6

795

115

0.02

F2

855

111

0.02

3

F3

969

8

<0.01

3

F4

1014

1663

0.24

1

G4

1446

521

0.07

3

H4

1008

22

3

H5

1289

3

H6

1763

SC

3

M AN U

0.05

239

0.55

154

0.35

3

0.01

F2

2091

3

F3

2940

2.20

<0.01

3

F4

3388

16

0.04

TE D

3

EP

G4

H5

AC C

1

3

RI PT

ACCEPTED MANUSCRIPT

43

2297

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

(b)

44

(a)

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

(c)

(d)

45

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

(e)

AC C

EP

TE D

Fig. 1

46

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

Fig. 2

47

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

(a)

48

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

(c)

AC C

EP

TE D

(b)

(d)

(e)

49

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

(f)

AC C

EP

TE D

Fig. 3

50

(g)

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

(a)

51

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

(b) Fig. 4

52

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

Fig. 5

53

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

(a)

54

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

(b) Fig. 6

55

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 7

56

ACCEPTED MANUSCRIPT

Highlights

EP

TE D

M AN U

SC

RI PT

Structural, thermal, and optical features of TeO2 based glasses were studied. Te–O–Te or O–Te–O linkages of TeO4, TeO3 and TeO3+1 were identified. Pr3+-doped glasses show high thermal and glass stabilities. Judd-Ofelt intensity parameters were evaluated from Pr3+absorption spectrum. Luminescence concentration quenching was observed at 2.0–5.0 mol % Pr3+ doping.

AC C

• • • • •