Journal of ELECTRONIC MATERIALS https://doi.org/10.1007/s11664-019-07198-3 2019 The Minerals, Metals & Materials Society Optical Characteristics of Dy3+ Ions in Alkali Fluoroborate Glasses for WLEDs SUBASH GOPI,1 P. REMYA MOHAN,1 E. SREEJA,1 N.V. UNNNIKRISHNAN,1 CYRIAC JOSEPH,1 and P.R. BIJU1,2 1.—School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam 686560, India. 2.—e-mail: [email protected] The aim of this study is to synthesize and characterize an economical alkali fluoroborate glass doped with Dy3+ ions using melt quenching technique for white light generation applications. The glasses under investigation are prepared from the precursor mixture keeping the molar composition 10K2O + 10BaO + 10ZnF2 + (70-x)B2O3 + xDy2O3, where x = 0.1 mol.%, 0.5 mol.%, 1.0 mol.%, 1.5 mol.% and 2.0 mol.%. Optical characterization techniques such as absorption, photoluminescence excitation, emission and decay analysis were accomplished to validate the use of the prepared glasses for white light emitting diodes. Optical band gap energy and vital Judd–Ofelt (JO) intensity parameters were derived using the absorption spectrum. The JO intensity parameters were used to explore some characteristic radiative parameters of the present glass system. The photoluminescence spectra of the glasses have been recorded at an excitation wavelength of 348 nm and the spectra contain two intense emission bands in the blue (480 nm) and yellow (572 nm) regions and a weak band in the red region (664 nm). With the increase of dopant ion concentration, the intensity of all emission bands marked a gradual increase. The variation of the ratio of integrated intensity of yellow band to blue band (Y/B ratio) with the concentration of Dy2O3 is also studied. Color coordinates determined using commission international de l’eclairage (CIE) 1931 suggest that the prepared glass can be a potential material for white light applications. The experimental lifetime values marked a significant decrease with increase in dopant ion concentration and the mechanism responsible for the quenching is identified. Quantum yield is determined experimentally as well as using JO theory. Key words: Fluoroborate, Judd–Ofelt theory, radiative properties, dipolequadrupole interaction INTRODUCTION White light emitting diodes (WLEDs) became a hot topic owing to their promising characteristics such as higher efficiency, better reliability, high brightness, excellent low-temperature performance, eco-friendly in nature, low voltage and better quality light output (low ultraviolet and infrared (Received August 4, 2018; accepted April 5, 2019) radiation).1–3 They can be fabricated either by combining the three primary colors (RGB) or by exciting a yellow phosphor using a blue emitting source. The former has low luminescence efficiency because of re-absorption of blue and thus not a wise choice. The second method, popularly known as phosphor-converted WLEDs (pc w-LEDs), has higher luminescence efficiency compared to the first method.4,5 But both of these methods use phosphors which must be encapsulated in the epoxy resin that faces serious issues as mentioned in literature.6,7 Gopi, Remya Mohan, Sreeja, Unnnikrishnan, Joseph, and Biju Nowadays, many researchers strive for improving the performance, durability, and cost-effectiveness of solid-state lighting applications and also to overshoot the problems associated with resin platform. The fascinating material in condensed matter physics, glass, is a favorable alternative to phosphors for the realization of white light emission as it does not require a resin platform. Attractive features like high transparency, simpler manufacturing process, free of halo effect, low cost, high thermal stability, ease of mass production and the epoxy resin free assembly make luminescent glasses more favorable for the preparation of WLEDs.8 Lowcost production and ease of manufacturing in different sizes and shapes make glasses containing rare earths more promising alternatives to single crystals and ceramic and plastic scintillators. Thus rare earth ion doped glasses gained immense attention from the scientific community for realizing white light. Rare earth (RE) doped glasses are potential candidate in a diverse area such as waveguide, optical fibers, solar concentrators, plasma display panel, optical amplifiers and many other.9 Optical properties of RE-doped glasses strongly depend on the host matrix. Oxide glasses are very functional for outstanding optical applications due to their dominant thermal stability and chemical durability and in particular, borate based glasses are worthy due to their unique characteristics like lower melting point, high transparency, better chemical durability, thermal stability, and good rare earth solubility compared to the other glasses. Structural properties of borate glasses can significantly be improved by the incorporation of network modifying oxides such as alkali metal oxides or alkaline earth metal oxides. These modifier oxides convert BO3 to BO4 unit without the formation of non-bridging oxygen. When two types of alkali ions are introduced into a glassy network keeping the total alkali content same, a non-linear variation in many physical properties of the matrix takes place and the phenomenon is popularly known as mixed alkali effect.10–12 New economical and efficient borate based glassy systems are still a hot topic due to the above said properties. Borate glasses doped with rare earth oxides have significant applications in many important fields.13–16 Among RE ions, the trivalent Dysprosium (Dy3+) ions in glasses are more interesting to study because of its intense emission in the visible spectral regions 470–500 nm (blue) and around 570–600 nm (yellow). The exact color from Dy3+ doped glasses depends on the relative integrated intensity ratio of yellow to blue emission (Y/B). Thus Y/B ratio is very crucial for Dy3+ doped materials and which is strongly rely on the host matrix. The yellow emission arising through the emission transition 4 F9/2 ﬁ 6H13/2 is a forced electric dipole transition and strongly influenced by the crystal field strength around the rare earth ion and red emission assigned to 4F9/2 ﬁ 6H11/2 is allowed electric dipole transition. Dy3+ ions also offer laser emission around 1.3 lm laser emission.17–19 As mentioned in the beginning, WLEDs are a hot topic of research and it has been a great interest in the development of new materials for their fabrication. The materials for the fabrication of WLEDs should be simultaneously effective and economical. Different spectroscopic studies such as optical absorption and decay analysis can give insight towards the suitability of a material for the fabrication of WLED. The present work is aiming at synthesizing and characterization of a new economic and chemically stable alkali fluoroborate glasses doped with dysprosium to check the suitability of these glasses for WLED applications. EXPERIMENTAL A molar composition 10K2O + 10BaO + 10ZnF2 + where x = 0.1 mol.%, (70-x)B2O3 + xDy2O3, 0.5 mol.%, 1.0 mol.%, 1.5 mol.% and 2.0 mol.% is used for the synthesis of the tile glass. About 10 g of the finely crushed homogeneous mixture was melted at around 950C and the resultant melt was poured onto a preheated thick brass plate at 350C and annealed at the same temperature for 12 h to remove thermal stress and strains. The as obtained samples were slowly quenched to room temperature. Finally, these glass samples were well polished to achieve smooth surfaces for optical and spectroscopic measurements. The UV–Vis-NIR absorption spectrum of the archetypical glass sample was recorded with a Varian Cary 5000 with a spectral resolution of 1 nm. Photoluminescence excitation (PLE), emission spectra (PL) and Quantum yield were taken using spectrofluorophotometer with xenon arc lamp (250 W) as an excitation source (Horiafluorolog-3 with an integrating sphere attachment). The luminescence spectra were also used to determine CIE1931 chromaticity co-ordinates. PL lifetime measurements were carried out on Edinburgh UV–VisNIR (FLS-980) spectrometer. The refractive indices of these glasses have been measured using J.AWoollam Co. EC-400 ellipsometer. RESULTS AND DISCUSSION An absorption spectrum is an efficient tool for the appraisal of the band structure and energy gap of amorphous as well as crystalline materials. Figure 1a depicts the optical absorption spectrum of a representative sample containing 2 mol.% of Dy2O3 in the UV–Vis region and Fig. 1b represents the absorption spectrum the same sample in the NIR region. Ten absorption bands are observed in the UV–Vis region are assigned as 6H15/2 ﬁ 4M17/2 (324 nm), 6 H15/2 ﬁ 4I9/2 (336 nm), 6H15/2 ﬁ 6P7/2 (349 nm), 6 H15/2 ﬁ 6P5/2 (364 nm), 6H15/2 ﬁ 4I13/2 (386 nm), 6 H15/2 ﬁ 4G11/2 (425 nm), 6H15/2 ﬁ 4I15/2 (453 nm), 6 H15/2 ﬁ 4F9/2 (472 nm), 6H15/2 ﬁ 6F3/2 (750 nm) Optical Characteristics of Dy3+ Ions in Alkali Fluoroborate Glasses for WLEDs Fig. 2. Tauc’s plot of 10K2O + 10BaO + 10ZnF2 + 68 B2O3 + 2Dy2O3 glass. Fig. 1. Optical absorption spectrum of 10K2O + 10BaO + 10ZnF2 + 68 B2O3 + 2Dy2O3 glass (a) in the UV–VIS region and (b) in the NIR region. and 6H15/2 ﬁ 6F5/2 (798 nm). The four absorption bands observed in the NIR region are 6H15/2 ﬁ 6F7/2 (897 nm), 6H15/2 ﬁ 6H7/2 (1089 nm), 6H15/2 ﬁ 6F11/2 (1268 nm) and 6H15/2 ﬁ 6H11/2 (1675 nm).20 The energy corresponding to the fundamental absorption edge is usually referred to as optical band gap energy, as glassy systems exhibit tailing of localized states into the forbidden energy gap. Optical band gap energy of the present glassy system is evaluated for the representative sample by using the relation given by Davis and Mott.21,22 The Tauc’s plot for the determination of optical band gap energy is illustrated in Fig. 2 and the as obtained value 3.83 eV is comparable with early reports on fluoroborate glassy systems.23–25 The intensity of an absorption band for an allowed transition is usually determined by oscillator strength which is directly proportional to the area under the absorption band. The experimental and calculated oscillator strengths are obtained using expressions available in previous literature.26,27 The least square fitting approach is carried out in the experimental and calculated oscillator strengths to evaluate the phenomenological JO intensity parameters Xk. The JO parameters have a vital role in exploring the local structure and bonding vicinity of RE ions in the host matrix. The JO parameter, X2 is correlated to the local structure of the RE ions and associated with the asymmetry and covalency between rare earth (RE) ions and ligand ions. On the other hand, parameters X4 and X6 are allied to the bulk properties of the host such as rigidity and viscosity. X2 is found to be the highest and which points towards the higher degree of covalence between Dy3+ ions and their surrounding ligands. Table I compares the JO parameters of the given glassy host with those obtained for some reported matrices. The present trend suggests the better quality of the prepared glasses as the ratio of X4 and X6 gives the value of spectroscopic quality factor. Thus the prepared glasses are suitable for optical device fabrication. The present value is also much closer to our own previous work in which Eu3+ ions were doped in the same host matrix and another approach for the evaluation of JO parameters was used.32 Thus the obtained result is consistent with the well-known fact that JO parameters are host dependent parameters and do not depend explicitly on the rare earth ion. As the dopant changes, the values of JO parameter changes only because of the modifications developed in the matrix. Table II compares fexp and fcal and the degree of fit between these oscillator strengths is expressed by the root mean square (rms) of oscillator strength (s). Recognizing suitable excitation wavelengths of Dy3+ ions in the prepared glasses is highly essential to explore luminescence characteristics. Figure 3 Gopi, Remya Mohan, Sreeja, Unnnikrishnan, Joseph, and Biju Table I. Comparison of JO intensity parameters of 10K2O + 10BaO + 10ZnF2 + 68 B2O3 + 2Dy2O3 glass with some previous reports X2 (3 10220) cm2 3.38 3.95 4.03 2.68 3.22 X4 (3 10220) cm2 X6 (3 10220) cm2 References 1.27 0.91 1.14 2.56 1.35 1.15 1.95 1.65 0.89 2.38 Present 28 29 30 31 Table II. Experimental and calculated oscillator strengths of different absorption transitions in 10K2O + 10BaO + 10ZnF2 + 68 B2O3 + 2Dy2O3 glass Oscillator strength Sl no. 1 2 3 4 5 6 7 8 9 10 11 12 13 Transition 6H15/2 ﬁ 6 H11/2 F11/2 6 H7/2 6 F7/2 6 F5/2 6 F3/2 4 F9/2 4 I15/2 4 G11/2 4 F7/2 4 P3/2 4 I11/2 4 I9/2 6 Fig. 3. Excitation spectrum B2O3 + 2Dy2O3 glass. of Band position (cm21) fexp (3 1026) fcal (3 1026) Deviation (3 1026) 5950 7887 9201 11140 12534 13321 21166 22170 23511 25811 27462 28637 29691 0.5400 3.1500 1.1900 1.0600 0.6300 0.2900 0.0530 0.2230 0.0613 0.7159 1.2100 2.0800 0.0385 0.5815 3.1455 1.3085 0.988 0.4434 0.0833 0.0753 0.1982 0.0423 0.1014 0.1961 1.7372 0.0758 0.0415 0.0045 0.1185 0.0720 0.1866 0.2067 0.0223 0.0248 0.0190 0.6145 1.0139 0.3428 0.0373 r = 0.353 10K2O + 10BaO + 10ZnF2 + 68 presents the excitation spectrum of the representative sample by monitoring the yellow emission at 572 nm. Well resolved excitation bands are observed at 323 nm (6H15/2 ﬁ 4M17/2), 336 nm (6H15/2 ﬁ 4I9/2), 348 nm (6H15/2 ﬁ 6P7/2), 363 nm (6H15/2 ﬁ 6P5/2), 385 nm (6H15/2 ﬁ 4I13/2), 424 nm (6H15/2 ﬁ 4G11/2), 456 nm (6H15/2 ﬁ 4I15/2) and 471 nm (6H15/2 ﬁ 4F9/2).20 It is clear from the spectrum that the band through the excitation transition (6H15/2 ﬁ 6P7/2) has greater intensity compared to others and thus 348 nm has opted as an excitation wavelength for luminescence studies. It can also be noted that intense bands are observed in the near UV and blue regions for the prepared glassy system, which is a prerequisite for the development of white-light-emitting devices by means of commercial blue InGaN/GaN LED chip.33 The luminescence spectra of the title glasses have been recorded under excitation at 348 nm. The excited Dy3+ ions relax non-radiatively to the metastable state (4F9/2) and from this level radiatively transfer to various lower levels as this level has sufficient energy gap of about 8000 cm1 with respect to the next lower level 6F3/2. As depicted in Fig. 4, Dy3+ ions give blue, yellow and red luminescence in the present glassy system. The spectra contain two intense emission bands in the blue region at 480 nm (4F9/2 ﬁ 6H15/2), the yellow region at 572 nm (4F9/2 ﬁ 6H13/2) and a weak band in red region at 664 nm (4F9/2 ﬁ 6H11/2). Further, no change in the shape or peak position of bands is observed from the emission spectra. The large line Optical Characteristics of Dy3+ Ions in Alkali Fluoroborate Glasses for WLEDs Fig. 4. Emission spectrum of 10K2O + 10BaO + 10ZnF2 + (70-x) B2O3 + xDy2O3 glasses. width observed in the spectra may be due to the inhomogeneous local fields around the luminescent centers in the present glassy system.34 Moreover, the yellow emission ascribed to the transition 4 F9/2 ﬁ 6H13/2 obeys the selection rule DL = ± 2; DJ = ± 2 is hypersensitive and its intensity is highly influenced by the environment around the Dy3+ ion in the host lattice.35 It is well known that yellow emission is often prominent when Dy3+ is located in low symmetry sites and becomes zero if located at sites with inversion center as electricdipole transitions are forbidden in those sites.36 The intensity of emission bands increases gradually with the concentration of Dy3+ ions in the given range of dopant ion concentration. The yellow emission band is almost a perfect Gaussian whereas the blue emission band seems to be split into components due to the partial lifting of degeneracy by the crystalfield around the Dy3+ ion.37 The (Y/B) intensity ratios of luminescence spectra have been evaluated since it is crucial in generating white light. In general, the Y/ B ratio is sensitive to the chemical composition of the host and not on the dopant concentration and as expected the ratio changes slightly in the present investigation. The variation of the integrated intensity of blue and yellow band is given as Fig. 5 and inset of which shows the variation of Y/B ratio with a concentration of Dy2O3. The variation in the intensity of the yellow band with different excitation wavelengths is also studied and given as Fig. 6. It can be seen that the highest intensity is obtained for the excitation wavelength 348 nm which is consistent with the excitation spectrum. JO theory gives a platform to envisage some important radiative properties. The required expressions are well discussed in the literature.38,39 All the radiative parameters for the emission transition from metastable state 4F9/2 are summarized in Table III. It can be observed that the crucial parameters such as branching ratio and emission cross section are the highest for the emission transition 4F9/2 ﬁ 6H13/2, which is consistent with Fig. 5. Variation of integrated intensity of blue and yellow emission bands 10K2O + 10BaO + 10ZnF2 + (70-x)B2O3 + xDy2O3 glasses. Inset figure shows the variation of Y/B ratio with different concentrations of Dy2O3. Fig. 6. Variation of intensity of yellow emission 10K2O + 10BaO + 10ZnF2 + 68 B2O3 + 2Dy2O3 glass. band of the recorded emission spectra. The stimulated emission cross-section is a measure of the rate of energy extraction from the optical materials using an external stimulus and is directly proportional to the total transition probability (A) of the emission bands.40 In order to validate the use of the prepared glassy samples for optoelectronic applications, the obtained radiative properties for the strongest yellow emission band is compared with some previous reports and given in the table. The higher stimulated emission cross-section and lower effective bandwidth of the emission band is a relevant feature for laser materials and it is noted from Table IV that the prepared glasses are better than Gopi, Remya Mohan, Sreeja, Unnnikrishnan, Joseph, and Biju Table III. Different radiative properties of 10K2O + 10BaO + 10ZnF2 + 68 B2O3 + 2Dy2O3 glass Transition 4 F9/2 ﬁ 6 H15/2 H13/2 6 H1/2 6 Dkeff (nm) Transition probability (s21) Emission cross section (3 10222 cm2) Gain bandwidth (3 10230 cm3) Optical gain (3 10225 cm2 s) 15.3 12.3 13.6 81 290.67 38.31 1.7 15.4 3.3 2.6 19 4.5 3.26 29.63 6.34 Table IV. Comparison of radiative properties of 10K2O + 10BaO + 10ZnF2 + 68 B2O3 + 2Dy2O3 glass with other reports Sl no. Dkeff (nm) Emission cross section (3 10222 cm2) Gain bandwidth (3 10230 cm3) Optical gain (3 10225 cm2 s) References 1 2 3 4 5 12.3 7.22 6.12 14.56 15.32 15.4 4.63 4.91 4.07 26.3 1900 334.8 912 3677 4029.1 29.63 0.516 1.85 17.48 15.043 Present 41 28 42 43 many of the previous reports for yellow laser applications. The exact color rendered by the prepared glass under 348 nm excitation can be predicted using CIE 1931 color coordinates which can be calculated using the equations well discussed in previous literature.44,45 Figure 7 illustrates the CIE chromaticity chart with color coordinates. The color coordinates for all glasses fall in the white region and is much closer to the blackbody locus. Thus the prepared glassy system can be suggested as a potential material for white light applications. McCamy gave an empirical formula for the determination of correlated color temperature (CCT) which is a vital parameter to monitor the quality of white light.46 Table V compares the CIE coordinates and CCT values of the present system with some previous reports. The CCT value of the present glass is also closer to that of daylight (5500 K) and commercial white light LED (6400 K) sources54 and thus the glass under investigation might be a promising material for WLED under UV excitation. The concentration dependent decay profiles of the metastable state 4F9/2 of Dy3+ ions in the present glasses are recorded by monitoring emission at 572 nm under an excitation of 348 nm and displayed as Fig. 8. It can be seen that the profiles follow almost single exponential up to a concentration of 0.5 mol.% and beyond this concentration, profiles exhibit non-exponential nature. The observed non-exponential behavior at higher concentration is attributed to the energy transfer between an excited Dy3+ and a Dy3+ ion in the ground state. The experimental lifetimes were evaluated from the profiles using the expression,35 Fig. 7. CIE chromaticity co-ordinates of 10K2O + 10BaO + 10ZnF2 + (70-x)B2O3 + xDy2O3 glasses. Inset figure shows the digital photograph of white emission in glass with x = 1.0 of Dy2O3 under UV radiation. sexp ¼ r tI ðtÞdt r IðtÞdt ð1Þ The lifetime values show a significant decrease from 0.58 ms to 0.08 ms with increasing dopant Optical Characteristics of Dy3+ Ions in Alkali Fluoroborate Glasses for WLEDs Table V. Comparison of CIE and CCT of 10K2O + 10BaO + 10ZnF2 + 68 B2O3 + 2Dy2O3 glass with other reports References CIE (x,y) CCT (K) Present 47 48 49 50 51 52 53 (0.33,0.37) (0.44,0.42) (0.44,0.44) (0.38,0.41) (0.33,0.34) (0.36,0.38) (0.34,0.31) (0.33,0.35) 5613 3080 3223 4332 5475 5516 5305 5439 Fig. 8. Decay profiles B2O3 + xDy2O3 glasses. of 10K2O + 10BaO + 10ZnF2 + (70-x) concentration. This quenching in lifetime arises due to the energy transfer by means of cross-relaxation and resonant energy transfer.55 The nonradiative relaxation processes strongly depend on the interionic distance. The concentrations 0.1 mol.% and 0.5 mol.% of Dy2O3 is very small and is much closer. The interionic distance in such low dopant concentration will be comparatively larger and the nonradiative interactions will be less. The comparatively greater lifetime of these samples is thus due to this fact. As concentration increases the interionic distance decreases and favors different inter-ionic interaction. But the interaction will be almost saturated after a particular distance. In the present investigation, the lifetime value of samples with high concentrations such as 1.5 mol.% and 2 mol.% of Dy2O3 are very close and it may be due to this saturation effect. In the sample with 1 mol.% of Dy2O3, the interactions are moderate and the lifetime value is well between the above mentioned concentrations. The partial energy level diagram given as Fig. 9 illustrates the overall excitation and emission schemes along with the possible crossrelaxation channels (CR1, CR2 and CR3) and resonant energy transfer (RET) channel in the prepared glasses. The spectral overlap between the excitation and emission spectra given as Fig. 10 underlines the possibility of resonant energy transfer within the prepared glasses. The non-exponential behavior at higher Dy2O3 concentrations has been investigated using the Inokuti–Hirayama (I–H) model according to which the intensity of luminescence decay with time [I(t)] is given as56 " 3=s # t C 3 t IðtÞ ¼ Ið0Þ exp C 1 ð2Þ s0 C0 s s0 where s0 is the lifetime of donor in the absence of acceptor, which is taken as the lifetime of sample containing 0.1 mol.% of Dy2O3 where the donor– acceptor interaction is negligible, ‘s’ is a critical parameter which can be 6, 8 or 10 for dipole–dipole, dipole–quadrupole and quadrupole–quadrupole interactions respectively. Its value h i can be obtained IðtÞ st0 versus st0 plot from the slope of ln ln Ið0Þ given in Fig. 11. The obtained value approximately equals to 8 suggests that dipole-quadrupole interaction is the dominant mechanism of energy transfer in the present fluoroborate glassy system. The total transition probability of the prepared glass sample with x = 1 mol.% using JO theory is determined as 501.79 s1 and the corresponding lifetime is 1.992 ms. The discrepancy in the experimental and calculated lifetime is probably due to several nonradiative processes within the sample. Quantum yield of the samples can be estimated as the ratio of experimental and calculated lifetimes. In the present investigation, it ranges from 29% to 4%. We have accurately measured the quantum yield experimentally. Figure 12a depicts the excitation of the sample and the blank (undoped) and Fig. 12b represents the emission of the same using an integrating sphere for quantum yield determination. The experimental quantum yield is found to be 51.34%. CONCLUSION A series of trivalent Dysprosium ion doped alkali fluoroborate glasses have been successfully synthesized by the conventional melt-quenching technique and characterized by using different spectroscopic Gopi, Remya Mohan, Sreeja, Unnnikrishnan, Joseph, and Biju Fig. 9. Partial energy level diagram and possible cross relaxation an resonant energy transfer channels of Dy3+ ions in alkali fluoroborate glasses. Fig. 10. Spectral overlap of excitation and emission 10K2O + 10BaO + 10ZnF2 + 68 B2O3 + 2Dy2O3 glass. of techniques. The JO intensity parameters followed a trend X2 > X4 > X6 in the present system. Using the phenomenological intensity parameters, various radiative properties were derived and are consistent with previous reports. The emission spectrum exhibit a gradual increase in intensity with increase in the concentration of Dy3+. It is found that the sample containing 2 mol.% of Dy2O3 has the highest h i Fig. 11. The plot of ln ln IIðð0t ÞÞ st0 versus st0 . intensity. CIE coordinates calculated using emission spectra suggest that the samples are capable of giving white light. The lifetime values of the fluorescent level were estimated and interaction responsible for lifetime quenching was explored. The experimental quantum yield of 51.34% makes the prepared glassy samples excellent for many Optical Characteristics of Dy3+ Ions in Alkali Fluoroborate Glasses for WLEDs Fig. 12. Quantum yield determination (a) sample and blank excitation (b) sample and blank emission. optoelectronic applications, especially W-LEDs. The obtained results conclude that the prepared glass is suitable for fabrication various optoelectronics devices, particularly for the production low cost white light emitting devices without a resin platform. ACKNOWLEDGMENTS The authors are thankful to UGC, India and DST, India for the financial assistance through SAP-DRS (No. F.530/12/DRS/2009(SAP-1)) and DST-PURSE (Grant No. DST-PURSE(SR/S9/Z-23/2010/22(CG))) programs respectively. 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