White Light Applications Research Articles

Luminescence and energy transfer mechanism in Eu3+/Tb3+-co-doped ZrO2 nanocrystal rods

Nanocrystal rods of Eu3+/Tb3+-co-doped ZrO2 were synthesized using a simple chemical precipitation technique. Both ions were successfully doped into the Zr4+ ion site in a mixed structure containing both monoclinic and tetragonal phases. The Eu3+ or Tb3+ singly doped zirconia produced red and green luminescence which are characteristics of Eu3+ and Tb3+ ions, respectively. The co-doped zirconia samples produced blue emission from defect states transitions in the host ZrO2, red and green luminescence from dopant ions giving cool to warm white light emissions. The phosphors were efficiently excited by ultraviolet and near-ultraviolet/blue radiations giving white and red light, respectively. The decay lifetime was found to increase with increasing donor ion concentration contrary to conventional observations reported by previous researchers. Weak quadrupole–quatdrupole multipolar process was responsible for energy transfer from Tb3+ (donor) ion to Eu3+ ion. No energy back-transfer from Eu3+ to Tb3+ ion was observed from the excitation spectra. Temperature-dependent photoluminescence shows the presence of defects at low temperature, but these defects vanished at room temperature and beyond. The Eu3+/Tb3+-co-doped ZrO2 nanocrystal rod is a potential phosphor for white light application using UV as an excitation source. Thermoluminescence measurements show that the inclusion of Tb3+ ion increases trap depths in the host zirconia.

Novel emission-tunable oxyapatites-type phosphors: Synthesis, luminescent properties and the applications in white light emitting diodes with higher color rendering index

Developing color-tunable phosphors via the introduction of co-doping activators and sensitizers to the host with energy transfer processes has been a state-of-the-art topic for a long time. In this work, novel emission-tunable oxyapatites-type Ba10(PO4)6O:Eu2+,Tb3+/Li+ phosphors were prepared via a high temperature solid state reaction for the applications in white light emitting diodes (w-LEDs) with higher color rendering index. Tunable colors from blue to green can be realized in the Ba10(PO4)6O:Eu2+,Tb3+/Li+ by varying the relative ratios of Eu2+ to Tb3+, showing good absorption in the range of 230–400 nm. The energy transfer mechanism from Eu2+ to Tb3+ ions was demonstrated to be a quadrupole-quadrupole interaction by combining the Inokuti-Hirayama (IH) model and Reisfeld's approximation. Importantly, a prototype white lamp was packaged by mixing Ba9.83(PO4)6O: 0.03Eu2+, 0.07Tb3+, 0.07Li+ and commercial red phosphor CaAlSiN3: Eu2+, and the lamp exhibits a higher color rendering index (Ra = 92 and R9 = 56) and warm correlated color temperature of 4361 K for the actual application. Better luminescent properties compared to commercial Y3Al5O12:Ce3+-based w-LEDs, indicating that Ba10(PO4)6O: Eu2+, Tb3+/Li+ phosphors are emerging as potential phosphor-converted w-LEDs.

Crystal structure and luminescence properties of self-activated phosphor CsDyP2O7

A new phosphor CsDyP2O7 has been prepared using a high temperature flux method and structurally characterized by single crystal X-ray diffraction analyses. Its structure can be characterized as a three-dimensional anionic framework of [DyP2O7]∞ that is constructed by PO4 tetrahedra and DyO6 octahedra, which delimited an 1D infinite channel running along the c-axis. Compound CsDyP2O7 was characterized by X-Ray diffraction (XRD), UV–vis absorption spectrum and Photoluminescence (PL) analyses. The excitation spectrum covers a wide range from 310 to 410nm, which suggests that the CsDyP2O7 phosphor can be effectively excited by a near-UV light source. The emission of CsDyP2O7 (348nm excitation) was observed at 484nm (blue) and 574nm (yellow) due to the 4F9/2→6H15/2 transitions and 4F9/2→6H13/2 transitions, respectively. The CIE chromaticity color coordinates (x=0.2882, y=0.3105) were found to be in the white light region. We may expect that self-activated phosphor CsDyP2O7 is a new candidate for pure white-light applications.

Broadly tuning Sm3+ emission via crystal field micro-modulation in CdMoO4 for white-LEDs

Rare earth activated oxides phosphors have attracted much attention in the field of solid state lighting (SSL) due to their irreplaceable advantages. In this work, a series of CdMoO4:aSm3+ and CdMoO4:aSm3+, M+ (M = Li, Na, K) phosphors were prepared by high temperature solid-state reaction. X-ray diffraction and photoluminescence spectroscopy were utilized to characterize samples properties. The concentration dependent luminescence of Sm3+ activated CdMoO4 sample was investigated in detail. The optimum doping concentration of CdMoO4:aSm3+ was 0.015 (1.5 mol%) and the corresponding concentration quenching mechanism was verified to be the electric dipole–dipole interaction. Also, CdMoO4:0.015Sm3+ phosphor exhibits bright red–orange emission with excellent CIE coordinates (x = 0.5887, y = 0.3908) under the excitation at 346 nm. In addition, it was observed that the luminescence intensity of Sm3+ and Na+ co-doped sample was 3.667 times stronger than that of the Sm3+ single doped sample under the same excitation wavelength. Meanwhile, when Na+ was incorporated into the CdMoO4 matrix, the color purity of CdMoO4:Sm3+ phosphor was enhanced from 78.0 to 81.3 %. These red–orange phosphors are promising for application in white light emitting diodes.

Synthesis and luminescence properties of MgO: Sm3+ phosphor for white light-emitting diodes

MgO: xSm3+ (0.02 ≤ x ≤ 0.08) red phosphors are prepared by low temperature solution combustion method. The MgO: XSm3+ phosphor characterized by X-ray diffraction (XRD), FT-IR, field emission scanning electron microscopy (FE-SEM), luminescence and decay time measurements. The results of XRD and FE-SEM show that resultant samples are single phase. The vibration properties MgO phosphor was studied by Fourier transform infrared spectroscopy. The luminescence spectra exhibits four emission bands at 566, 603, 651 and 708 nm corresponding to the various transition from 4G5/2 ground state to lower lying levels 6H5/2, 6H7/2, 6H9/2 and 6H11/2 states, with an excitation wavelength at 404 nm. The chromaticity coordinates have been estimated from the emission spectra and the suitability of title phosphor for white light applications. The lifetime corresponding to the 4G5/2 level of the title phosphor has been found to decrease with the increase in Sm3+ ion concentration.

Flexible silica films encapsulating hydrophilic CdTe quantum dots for application in white light emitting diodes

Large flexible silica films encapsulating hydrophilic CdTe quantum dots (QDs) were fabricated via controlling the hydrolysis of 3-aminopropyltrimethoxysilane (APS). Hydrophilic CdTe quantum dots with green to red emitting were encapsulated in the films through a sol–gel incorporation process for retaining high photoluminescence (PL) efficiency and stability. Fluorescence microscopy and a scanning electron microscopy were employed to examine dispersion of CdTe QDs in the emitting films, which illustrated that structure of silica films was uniform. The PL stability of these flexible silica films was investigated in argon condition, the PL properties of the films encapsulated green-, yellow-, and red-emitting CdTe QDs were very stable. Furthermore, the silica-CdTe QDs emitting films revealed high PL stability under ultraviolet (UV) light irradiation, proper concentration of QDs in silica films can make the films more stable. In addition, different emission flexible silica-CdTe QDs films with large area were obtained. The dual-emitting silica-CdTe QDs films exhibited coordinates (0.384, 0.350) in the Commission Internationale de I׳Eclairage (CIE) chromaticity diagram under blue light as excitation source. Due to flexibility, adjustable colors, high stability, large area, easy to operate, silica-CdTe QDs emitting films show potential application in lighting devices and flat panel displays.

Influence of Modifier Cations on the Spectroscopic Properties of Dy3+ Doped Telluroborate Glasses for White Light Applications.

The effect of electronegativity and ion size of the modifier cations have been analyzed through a new series of Dy3+ doped telluroborate glasses prepared by melt quenching technique with the composition of 30TeO2+29.5B2O3+20MO+20MF2+0.5Dy2O3 (where M=Ba2+, Sr2+, Zn2+, Cd2+ and Pb2+). The various stretching and bending vibrational modes of borate and tellurite network have been identified through FTIR spectral measurements. The conversion of BO3 units into BO4 units increases NBOs in the glass network and the same is confirmed through FTIR spectra. The nephelauxetic ratio ([Formula: see text]) and bonding parameter (δ) value reveals that the Dy-O bond in prepared glasses possesses ionic nature. JO intensity parameters (Ω2, Ω4 and Ω6) of the present glasses follow the trend Ω2>Ω4>Ω6 uniformly in all the prepared glasses. Radiative parameters like transition probability (A), stimulated emission cross section[Formula: see text], branching ratio (βR) values have been predicted from the absorption spectra of Dy3+ ions using JO theory. Among the prepared glasses TBZnD glass posses a better CIE 1931 colour chromaticity coordinates (0.33, 0.39) and CCT value (5019K). Decay profile of 4F9/2 state of the Dy3+ ion exhibits non-exponential nature due to the interaction between Dy3+-Dy3+ ions. The nature of interaction between Dy3+-Dy3+ ions has been analyzed through Inokuti-Hirayama model and the best fit of S=6 indicates that the dipole-dipole interaction is responsible for the energy transfer between Dy3+-Dy3+ ions. The glass containing Zn2+ ions posses encouraging results such as higher Y/B intensity ratio, stimulated emission cross section and higher branching ratio (4F9/2→6H13/2). Thus the present study identified the Zn2+ ions as a better modifier ion to develop the Dy3+ doped glasses for various photonic applications.

A New Green Phosphor Using Solid-Solution and Their Structural and Optical Properties

Garnet structure (cubic, space group Ia-3d) is recognized as highly stable and efficient host for white solid state lighting application. However, yellow Y3Al5O12:Ce3+ phosphor is associated with patent infringement while a replacement of yttrium with lutetium of form a similar structure Lu3Al5O12:Ce3+ (LuAG:Ce3+) phosphor would raise the cost of the LED device. The solid-solution design is an efficient route to develop new phosphors with various compositions. The commonly used solid-solution design method concentrates on the cation/anion substitution. The benefits vary from the color tuning of the peaking emission, to improved structural rigidity or chemical stability.(1) Garnet structure which accommodates wide variety of cations can be chosen as a template for such solid solutions. In this study, we report a new green-emitting phosphor, the Ce3+-doped garnet, which has better luminescence properties than the commercial LuAG:Ce3+phosphors. The influence of expanding substituted site by solid-solution and the change of photoluminescence intensity have been explored, and established their correlation. By the fabrication of white laser diodes, we explored its potential suitability in white laser diodes applications. This suggests that the phosphor displays great potential for application in white light generation using blue laser diodes. 1. W. B. Im, N. George, J. Kurzman, S. Brinkley, A. Mikhailovsky, J. Hu, B. F. Chmelka, S. P. DenBaars and R. Seshadri, Advanced Materials, 23, 2300 (2011). Figure 1. Photoluminescence excitation spectra and emission spectra of optimized sample by solid-solution and commercial LuAG:Ce3+phosphor at room temperature. Figure 1

Hydrogen-related complexes in Li-diffused ZnO single crystals

Zinc oxide (ZnO) is a wide band gap semiconductor and a potential candidate for next generation white solid state lighting applications. In this work, hydrogen-related complexes in lithium diffused ZnO single crystals were studied. In addition to the well-known Li-OH complex, several other hydrogen defects were observed. When a mixture of Li2O and ZnO is used as the dopant source, zinc vacancies are suppressed and the bulk Li concentration is very high (>1019 cm−3). In that case, the predominant hydrogen complex has a vibrational frequency of 3677 cm−1, attributed to surface O-H species. When Li2CO3 is used, a structured blue luminescence band and O-H mode at 3327 cm−1 are observed at 10 K. These observations, along with positron annihilation measurements, suggest a zinc vacancy–hydrogen complex, with an acceptor level ∼0.3 eV above the valence-band maximum. This relatively shallow acceptor could be beneficial for p-type ZnO.

Tailoring the luminescence of Eu3+ co-doped Dy3+ incorporated aluminofluoro-borophosphate glasses for white light applications

Co-doping of Eu3+ ions in Dy3+ single doped glasses improves white light emission. This manuscript reports correlation between the structural rearrangement and its effect on the optical properties of the title glasses. The nephelauxetic effect on absorption transitions have been used to elucidate the bonding nature of the RE3+ ions with their surrounding ligands. It reveals the predominant ionic nature of the dysprosium bonds while that of Eu ions exhibit covalent nature. Effect of Eu3+ ions on the symmetry of the ligand field around the Dy3+ ions have been predicted using JO theory and asymmetric (Y/B) intensity ratio. It is found that asymmetry around Dy3+ ions increases with Eu3+ ions concentration. Tuneable nature of the white light emission from the Eu3+/Dy3+ co-doped aluminofluoro-borophosphate glasses was confirmed through the CIE 1931 chromaticity coordinates for glasses containing different concentrations of europium. The energy transfer process takes place between Dy3+ and Eu3+ ions has also been confirmed through lifetime measurements. Fitting the decay curves using IH model thus reveal the dipole–dipole nature of interaction.

Photoluminescence properties of a novel red-emitting phosphor Eu3+ activated scandium molybdate for white light emitting diodes

A series of red-emitting phosphors of Sc2(MoO4)3: x%Eu3+ have been successfully synthesized at 800°C by solid-state reaction. X-ray diffraction, scanning electron microscopy, photoluminescence spectra and decay curves were used to characterize the structures and luminescence properties. In the excitation spectrum, the strongest absorptions of 7F0⿿5L6and 7F0⿿5D2 match well with the emission wavelength of the near-ultraviolet InGaN and blue GaN chips. The CIE value of Sc2(MoO4)3: 40%Eu3+ sample reaches (0.665, 0.334), which is very close to the NTSC standard (0.67, 0.33), demonstrating the highly pure red lights emitted. The decay curves of Eu3+: 5D0⿿7F2 emission exhibit a bi-exponential function excited by a 266nm nanosecond-pulsed laser resulting from the lattice distortion which can speed up electric dipole transition. The good excitation profile and pure red emission indicate Sc2(MoO4)3: Eu3+ is a promising red-emitting phosphor for its application in commercial white light emitting diodes.

Effect of Tb3+ concentration on Sm3+ doped leadfluoro-borophosphate glasses for WLED applications

A new series of Sm3+/Tb3 co-doped leadfluoro-borophosphate glasses with the composition 50B2O3+(19.5−x)P2O5+10Li2O+10ZnF2+10PbO+0.5Sm2O3+xTb2O3 (where x=0, 0.05, 0.1, 0.25, 0.5, 1 and 2 in wt%) have been prepared following the melt quenching technique. The presence of fundamental vibrational groups such as BO3, BO4 and PO4 were explored through the FTIR and Raman spectral measurements. The nephelauxetic effect on the absorption transitions have been used to elucidate the bonding nature of the Sm3+ ions with the surrounding ligands thus reveal the predominant ionic nature. Effect of Tb3+ ions on the symmetry of the ligand field around the Sm3+ ions have been predicted using asymmetric intensity ratio values. It is observed that asymmetry around the Sm3+ ion increases with Tb3+ ion concentration upto 1wt% due to the chaos of both the rare earth ions and after that Tb3+ ion concentration dominates thus in-turn creates lower asymmetrical environment. Luminescence quenching effect due to the presence of RE3+ ions concentration has never seen upto almost 2.5wt% (for both RE ions) hence the present host possess the capability to incorporate more number of RE ions. The decay profile of the Tb3+ ion (5D4) is found tobe single exponential and Sm3+ ion (4G5/2) is found to be non-exponential nature. The decreasing trend in the experimental lifetime value of the Tb3+ ions confirms the energy transfer process takes place from Tb3+ ions to Sm3+ ions and the interaction takes place between Tb3+ and Sm3+ ions is of dipole-dipole nature and the same is analyzed using IH model. The energy transfer efficiency is found to increase from 47% to 54% with Tb3+ ion concentration. The CIE color chromaticity coordinates have been calculated to identify the characteristic emission of the prepared glasses and the correlated color temperature, color purity were also determined. All these results suggest that, BPLS0.5T glass is a potential candidate for warm white light applications with minimal blue hazards.

Enhancing selectively red spectral region by photonic crystals toward white light emission

The combination of red, green, blue (RGB) dyes and photonic crystals (PCs) is explored for white light application. The results show RGB emission is difficult to program by fluorescence resonance energy transfer, which is impossible to achieve the white light emission. When the PCs is used as an optical substrate, the green and blue spectral components obtain 2.7–3.5 times enhancement compared with the control sample due to large surface area of PCs. More importantly, the enhancement ratio of red spectral component is higher than that of the other color in the case of the stopband of PCs overlapping emission wavelength of Nile red, resulted from the enhanced light extraction of PCs, which makes up for the lack of red light, so that CIE coordinates are approaching to the white light region. The strategy will be of great guideline toward white light emission and play an important role on developing novel lighting devices.

Preparation and spectroscopic investigation of novel NaAlP2O7:Eu2+ phosphors for white LEDs

NaAlP2O7:Eu2+ phosphors were prepared by a solid state reaction. The structure, Fourier transform infrared spectra, photoluminescence spectra and fluorescence decay curves of NaAlP2O7:Eu2+ were investigated. These phosphors can be excited over a broad range and generate a greenish-blue emission band peaking at 459 nm. The critical quenching concentration of Eu2+ in NaAlP2O7:Eu2+ phosphors is about 3 mol% and the corresponding concentration quenching mechanism is demonstrated to be dipole-dipole interactions. Meanwhile the critical distance for concentration quenching is determined to be 19.7 Å. As the temperature increases from 25 to 150 °C, the emission intensity of NaAlP2O7:0.03Eu2+ still possesses 86.7% of its initial PL intensity, indicating its high thermal stability. All the results suggest that the NaAlP2O7:Eu2+ phosphors are promising greenish-blue-emitting phosphors for application in white light emitting diodes.

Synthesis and optical characterization of color-tunable heterocyclic ligand based beryllium(II) complexes for white lighting applications

Beryllium(II) complexes with 2-(1H-benzimidazole-2-yl)phenol (HBI) and 8-quinolinol (q) or 5-chloro-8-quinolinol (Clq) or 2-methyl-8-quinolinol (Meq) or 5.7-dimethyl-8-quinolinol (Me2q) were synthesized and characterized. All prepared materials exhibited good thermal and electrochemical stability. The synthesized metal complexes showed bright emission on excitation with an ultraviolet light source. UV–visible absorption and photoluminescence (PL) emission spectra were recorded in order to investigate the photophysical characteristics of prepared metal complexes. The optical band gap of synthesized materials was found in the range of 3.19–3.36eV. The beryllium(II) complexes in solid state showed emission at 479nm for [BeHBI(q)], 481nm for [BeHBI(Clq)], 471nm for [BeHBI(Meq)] and 516nm for [BeHBI(Me2q)] materials. Temperature-dependence photoluminescence spectrum of [BeHBI(q)] complex was also studied to illustrate the effect of the substituents on the emission intensity and peak position of the spectrum. The minimal energy three dimensional molecular structures and the frontier molecular orbitals of prepared metal complexes were computed by the density functional theoretical (DFT) calculations using B3LYP correlation functional and 6-31G(d,p) basis set. The structural and the photophysical characteristics of metal complexes were tuned with introduction of electron donating group (EDG) and electron withdrawing group (EWG) on the 8-quinolinol ligand. Complexes emitting color tuned luminescence could be utilized for various field emissive devices.

A New Blue-Emitting Mg2Al4Si5O18:Ce3+ Phosphor for White Light Emitting Diodes.

A series of blue-emitting Mg2Al4Si5O18:Ce3+ phosphors were prepared via the conventional high temperature solid-state reaction method. The phase structure, photoluminescence (PL) properties, PL thermal stability, and fluorescence decay curves of the samples were investigated for the first time. Under excitation at 365 nm, the phosphor exhibited a broad band blue emission with peak at 440 nm, which was ascribed to the 4f --> 5d transition of Ce3+, and the color coordinate was (0.1602, 0.0849). When the temperature increased to 150 °C, the luminescence intensity of the Mg2Al4Si5O18:0.06Ce3+ phosphor was 55.73% of the initial value at room temperature. The activation energy ΔE was calculated to be 0.25 eV, which proved the good thermal stability of the sample. The energy transfer critical distance between Ce3+ ions in Mg2Al4Si5O18 host were also calculated. The above results indicate that the Mg2Al4Si5O18:Ce3+ is a promising candidate as a blue-emitting near ultraviolet convertible phosphor for application in white light emitting diodes (WLEDs).

Enhancement of Photoluminescence in BaSi2O2N2:Eu2+ by Partial Ge4+ Substitution for Si4+.

Ge4+-doped BaSi2O2N2: Eu2+ phosphors were prepared by a high temperature solid-state reaction method. The phase structure, photoluminescence (PL) properties and PL thermal stability of the as-synthesized samples were investigated. The emission intensity of the Ba(Si0.99Ge0.01)2O2N2: 0.05Eu2+ phosphor was 41.7% greater than that of BaSi2O2N2:0.05Eu2+. When the temperature increased to 150 °C, the emission intensity of Ba(Si0.99Ge0.01)2O2N2:0.05Eu2+ phosphor was 67.0% of the initial value at room temperature. This value was 22.9% greater than that of BaSi2O2N2:0.05Eu2+. The related mechanism has also been explained through the crystal field theory. All these results indicated that the Ge4+-doped BaSi2O2N2:0.05Eu2+ phosphor is a promising material for application in white light emitting diodes.

Crystal structure, energy transfer mechanism and tunable luminescence in Ce3+/Dy3+ co-activated Ca20Mg3Al26Si3O68 nanophosphors

Ce3+, Dy3+ and Ce3+/Dy3+ co-doped Ca20Mg3Al26Si3O68 (CMAS) nanophosphors were synthesized via modified solution-combustion method. Sharp X-ray diffraction patterns confirmed the formation of pure crystalline phase of Ca20Al26Mg3Si3O68 as an orthorhombic crystal system having space group Pmmn. The phase purity of as synthesized material has allowed reliable structural parameters to be obtained from the Rietveld analysis of its powder diffraction pattern. The Ce3+, Dy3+ and Ce3+/Dy3+ emission at different lattice sites in CMAS host has been identified and discussed. Under ultra-violet (UV) excitation, optical properties and the energy transfer mechanism from Ce3+ to Dy3+ in CMAS: Ce3+/Dy3+ nanophosphors have been elaborated by photoluminescence spectroscopy. Also, the effects of doping and sintering temperature on the structure of prepared CMAS host samples have been investigated in detail. The Ce3+/Dy3+ concentration quenching mechanism due to multipole–multipole interaction has been studied and the critical energy-transfer distance was calculated to be 7.8Å. The band gap of the synthesized phosphors was calculated from diffuse reflectance spectra using the Kubelka–Munk function. A uniform layered structure network has been revealed in scanning electron microscopy images of the CMAS phosphor. Transmission electron microscopy results indicate nanocrystalline nature of synthesized phosphors. CMAS: 1m% Ce3+ and CMAS: 0.5m% Dy3+ nano-luminescent powders are promising candidate as a blue and blue–yellow emitting UV convertible phosphor for application in white light emitting diodes. By utilizing the energy transfer mechanism in present CMAS: Ce3+/Dy3+ nanophosphors, with an appropriate tuning of the activator content, these phosphors can exhibit great potential for white light emission, as single-emitting component phosphors in solid state lighting technology.

Structural and optical investigations on Dy3+doped lithium tellurofluoroborate glasses for white light applications

Dy3+doped lithium tellurofluoroborate glasses were prepared with the chemical composition (40–x)B2O3+15TeO2+15Li2O+15LiF+15NaF+xDy2O3 (BTLNxD; where x=0.05, 0.1, 0.25, 0.5, 1.0 and 2.0 in wt%) following conventional melt quenching technique and characterized through FTIR, optical absorption, luminescence and lifetime measurements. The vibrations of the borate and tellurite network have been identified through FTIR spectral measurements. The optical properties have been explored from the absorption and luminescence spectra. The optical band gap of direct and indirect allowed transitions was determined from Tauc׳s plot and the variations in the band gap energy with structural arrangements in the prepared glasses is also discussed. Judd–Ofelt theory has been used to evaluate the intensity parameters Ω2, Ω4 and Ω6 using the experimental oscillator strengths and absorption energy levels. The radiative parameters such as transition probability (A), stimulated emission cross-section (σPE), branching ratios (βR) and radiative lifetime (τR) corresponding to the 4F9/2→6H11/2, 6H13/2 and 6H15/2 emission transitions were calculated from the luminescence spectra. The yellow-to−blue (Y/B) luminescence intensity ratios and colour chromaticity coordinates of the title glasses have also been estimated to evaluate the white light emission as a function of Dy3+ion concentration. These results have been used to identify the suitability of the prepared glasses for W-LED applications. The decay rates for the 4F9/2 level have been measured and found to deviate from exponential to non-exponential nature with the increase of Dy3+ion concentration. The non-exponential decay rates have been fitted with the Inokuti–Hirayama model for S=6 which indicate that dipole–dipole mechanism is responsible for the energy transfer processes through Dy3+–Dy3+interaction.

A Tunable-Color Emission Phosphor Y₂O₃:Eu³⁺, Bi³⁺ with Efficient Energy Transfer for White Light Emitting Diodes.

The Eu³⁺, Bi³⁺ ions co-doped Y₂O₃ phosphor has been synthesized by the conventional solid-state reaction method, and its photoluminescence (PL) spectra are investigated for application in white light emitting diode (LED). The Eu³⁺, Bi³⁺ ions co-doped Y₂O₃ phosphor showed a characteristic emissions with greenish blue and red color upon the near-UV light in the range of 310-360 nm, originating from ³P₁ --> ¹S₀ transition of Bi³⁺ and ⁵D₀ --> ⁷F(J) transition of Eu³⁺, respectively. As 613-nm emission of Eu³⁺ ions is monitored, excitation spectrum consists of two broad peaks near 230 nm and 330 nm, ascribed to the Eu³⁺-O²- charge transfer band (CTB) and the transition from the ground state to the excited states of Bi³⁺ ions, respectively. It implies that the energy transfer from Bi³⁺ ions to E³⁺ ions occur and the phosphor's color may be controlled by adjusting the concentrations of Eu³⁺ ions and Bi³⁺ons in Y20₂O₃The availability of this strategy is demonstrated in this work, and white light can be realized with superior chromaticity coordinates of (x = 0.337, y = 0.328) and a CCT of 5284 K for Y20₂O₃% Eu3+³⁺0.1% Bi3+³⁺Thus, it will be a promising candidate for the ultraviolet excitation white light emitting diode (LED).