Color-tunable luminescence performance of single-component Na5Y(MoO4)4:Dy3+, Tm3+ white-emitting phosphor for white light-emitting diodes

The single-component Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ white-emitting phosphor was prepared by the sol-combustion method, and Tm³⁺ was codoped for color-tunable white emission. The XRD patterns confirm that the as-prepared samples have a Na₅Y(MoO₄)₄ structure and do not change with Dy³⁺/Tm³⁺ codoping. Under ultraviolet excitation at 352 nm, the Na₅Y(MoO₄)₄:Dy³⁺ phosphor shows a characteristic white emission consisting of a weak peak at 485 nm and a strong peak at 577 nm. By codoping a small amount of Tm³⁺, the blue emission of phosphor is enhanced, and the chromaticity coordinates can be adjusted between (0.3663, 0.416) and (0.319, 0.3407); thus, color-tunable white emission is achieved with the synergistic effect of Dy³⁺ and Tm³⁺. The luminescence intensity of Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ at 483 K still retains 72% of the initial intensity, showing excellent thermal stability. By combining Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ with a 365 nm chip, the fabricated w-LED device emits bright white light for illumination. Therefore, the as-prepared Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ has potential applications in the field of w-LEDs as white-emitting phosphors.     

Tunable single-phased white-emitting Sr3Y(PO4)3:Dy3+ phosphors for near-ultraviolet white light-emitting diodes

Single-component white-emitting Sr₃Y(PO₄)₃:Dy³⁺ phosphors were synthesized by a high-energy deformation process. X-ray diffraction patterns showed the resulting crystallized phase to be of cubic structure, space group I-43d (no. 220). The broad-band excitation spectra between 250 and 500 nm were observed by monitoring the emission wavelength at 576 nm, which matches well with commercial near-UV or blue LED chips. Under a 352 nm excitation, the emission peaks were observed at 483 nm (blue), 576 nm (yellow), and 666 nm (red), corresponding to the ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2, and ⁴F_9/2 → ⁶H_11/2 transitions of Dy³⁺ ions. The optimized doping concentration of Dy³⁺ ion was 8 mol%. By controlling the Dy³⁺ ion concentration, tunable colors from white to yellow were obtained in Sr₃Y(PO₄)₃:Dy³⁺ phosphors. These results reveal that studied materials may be a promising candidate for white LED applications.     

Tunable luminescence and energy transfer properties of MgY4Si3O13: Ce3+, Tb3+, Eu3+ phosphors

The tricolor-emitting MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors for ultraviolet-LED have been prepared via a high-temperature solid-state method. X-ray diffraction, photoluminescence emission, excitation spectra and fluorescence lifetime were utilized to characterize the structure and the properties of synthesized samples. Two different lattice sites for Ce³⁺ are occupied from the host structure and the normalized PL and PLE spectra. The emissions of single-doped Ce³⁺/Tb³⁺/Eu³⁺ are located in blue, green and red region, respectively. The energy transfer from Ce³⁺ to Tb³⁺ and from Tb³⁺ to Eu³⁺ has been validated by spectra and decay curves and the energy transfer mode from Tb³⁺ to Eu³⁺ was calculated to be electric dipole-dipole interactions. By adjusting the content of Tb³⁺ and Eu³⁺ in MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺, the CIE coordinates can be changed from blue to green and eventually generate white light under UV excitation. All the results indicate that the MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors are potential candidates in the application of UV-WLEDs.     

Deep blue,cyan, orange-red,and white multicolor emissions generated by Bi3+/Eu3+ activated KBaYSi2O7 luminescent materials for white light-emitting diodes

A variety of Bi³⁺ and/or Eu³⁺ doped KBaYSi₂O₇ phosphors with deep blue, cyan, orange-red, and white light multicolor emissions have been fabricated by a Pechini sol-gel (PSG) method. The KBaYSi₂O₇:Bi³⁺ phosphors exhibit an intense cyan emission or a unique narrow deep blue emission when excited by different wavelengths, which may bridge the cyan gap or act as a promising deep blue phosphor for white light-emitting diodes (WLEDs). The tunable multicolor emissions can be achieved by changing the Bi³⁺ doping concentrations. The Bi³⁺/Eu³⁺ co-doped KBaYSi₂O₇ phosphors display intrinsic emissions of Bi³⁺ and Eu³⁺ and an energy transfer process between Bi³⁺ and Eu³⁺ can be detected. The luminescence colors of KBaYSi₂O₇:Bi³⁺,Eu³⁺ regularly shift from blue, through cold and warm white, finally toward orange-red by adjusting the relative doping concentrations of Bi³⁺ and Eu³⁺. The single-phase white light-emitting material can be generated in both cold and warm white regions by simply varying the Eu³⁺ doping concentrations. Furthermore, three kinds of WLEDs devices are fabricated by KBaYSi₂O₇:Bi³⁺ or KBaYSi₂O₇:Bi³⁺,Eu³⁺ phosphors, which can exhibit dazzling white light emissions with eminent CIE coordinates, correlated color temperature, and color rendering index. The result offers direct evidence that the as-synthesized phosphors may be potentially applied in WLEDs and solid-state lighting.     

A novel single-phase Na3.6Y1.8(PO4)3:Bi3+,Eu3+ phosphor for tunable and white light emission

A new type of Bi³⁺,Eu³⁺ single- and co-doped Na_3.6Y_1.8(PO₄)₃ phosphate phosphors were manufactured using conventional high-temperature solid-state reaction technique to explore their application for solid-state lighting. The crystal structure, luminescent properties, luminescent mechanism and quantum efficiency were thoroughly explored. Results show that there are two crystallization sites for Bi³⁺ and Eu³⁺ ions. Upon the excitation of 342 and 373 nm, Bi³⁺ single-doped phosphors exhibit green and blue emission, derived from the ³P₁ to ¹S₀ transition of Bi³⁺ located in different occupancy sites. Thanks to radiative energy transfer process from Bi³⁺ to Eu³⁺, adjustable emission could be acquired by altering Eu³⁺ content in co-doped phosphors. Pure white-light emission with quantum efficiency value of 22.9% can be realized in Na_3.6Y_1.8(PO₄)₃:0.01Bi³⁺,0.1Eu³⁺ sample and the integrated intensity of white light emission at 417 K remains 85% of that at room temperature. Our results indicate that Na_3.6Y_1.8(PO₄)₃:Bi³⁺,Eu³⁺ phosphors have feasible application in high-power ultraviolet driven solid-state lighting.     

Synthesis,energy transfer and multicolor luminescent property of Eu3+-doped LiCa2Mg2V3O12 phosphors for warm white light-emitting diodes

In this study, Eu³⁺-doped LiCa₂Mg₂V₃O₁₂ (LCMVO) phosphors with multicolor luminescent property were prepared by the solid phase reaction. Their structure, morphology and luminescent property were studied systematically by X-ray diffraction, scanning electron microscope and photoluminescence spectra. The LCMVO phosphors showed pure cubic crystal structure with space group ($Ia\overline{3}d$) and irregular spherical morphology. The excitation spectra showed a strong absorption to ultraviolet light. Under the excitation wavelength at 360 nm, they exhibited a cyan emission with a luminescence center at 520 nm. When Eu³⁺ ions were doped into LCMVO system, the Eu³⁺ characteristic emissions were also observed and the emission colors were tuned from cyan to orange via adjusting Eu³⁺ ion concentration. Further, electric dipole-quadrupole interaction and luminescence decay curves were adopted to explain the energy transfer from (VO₄)^3- to Eu³⁺. The emission spectra of as-obtained phosphors at different temperature were measured to evaluate their thermal stability. The quantum efficiency values were measured to be 42.5% for LCMVO host and 38.6% for LCMVO: 0.01Eu³⁺ sample. The final prepared LED lamp showed easeful warm white light with suitable Ra of 89 and CCT of 3847 K, respectively. These results suggest LCMVO phosphors may be applied in near ultraviolet chip-excited white light-emitting diodes.     

White light emitting from YVO4/Y2O3:Eu3+,Bi3+ composite phosphors for UV light-emitting diodes

A series of (1−x)YVO₄/xY₂O₃:Eu³⁺_0.006,Bi³⁺_0.006 (0≤x≤0.54) composite phosphors was synthesized in one step by high temperature solid state reaction and the photoluminescence properties were investigated. By means of co-doping Eu³⁺ and Bi³⁺ ions into the composite matrices composed of YVO₄ and Y₂O₃ crystals, the YVO₄/Y₂O₃:Eu³⁺,Bi³⁺ phosphor exhibits simultaneously the blue (418 nm), green (540 nm) and orange-red (595, 620 nm) emissions. The broad blue and green emissions are attributed to the ³P₁–¹S₀ transitions of Bi³⁺ ion both in Y₂O₃ and in YVO₄ matrices. Moreover, the sharp orange-red emissions are attributed to the ⁵D₀–⁷F_1,2 transitions of Eu³⁺ ion in YVO₄ matrix. By tuning the mole ratio of YVO₄/Y₂O₃ matrices the white light-emitting could be obtained. The results indicated that when the mole ratio of Y₂O₃ (x) is at 0.11–0.54 mol, the (1−x)YVO₄/xY₂O₃:Eu³⁺_0.006,Bi³⁺_0.006 phosphors emit white light by combining the blue, green and orange-red emissions under the excitation of 360–370 nm wavelength which matches the emission of the commercial UV-LED diode. This implies that the phosphors may be the promising white light materials with broad absorption band for white light-emitting diodes.     

YVO4:Eu3+,Bi3+荧光粉的制备及荧光性能研究

用溶胶凝胶法在较低温度下制备了YVO4:Eu3+,Bi3+荧光粉,采用X射线衍射仪(XRD),扫描电子显微镜(SEM)及荧光分光光度计测试,研究了合成产物的结构、表面形貌,分析了在Eu3+含量一定的情况下掺杂Bi3+的浓度的变化对发光性能的影响.结果表明,溶胶凝胶法合成的YVO4:Eu3+,Bi3荧光粉为单相结构、粒径在1 μm左右、无团聚现象;Bi3+对Eu3+离子有敏化作用,在一定浓度下使荧光粉的发射强度增加.     

Ca5Ga6O14:Eu3+: A novel phosphor with outstanding heat resistance for white light-emitting diodes

A novel red-emitting phosphor Ca₅Ga₆O₁₄:Eu³⁺ has been synthesized using solid-state method. The excitation and emission spectra show that the phosphor can emit the red light with the main peak at 611 nm under excitation of the 280 and 393 nm UV chip and the optimal Eu³⁺ concentration is determined to be x = 0.07. Analysis of emission spectrum shows that Eu³⁺ occupy the center of noninversion symmetry. With the increase of Eu³⁺ doping concentration, the decay time is prolonged due to deeper energy trap arising from nonequivalent substitution. Additionally, the measured thermal stability with 0.539 eV activation energy and calculated 90.5% color purity of optimal phosphor indicate that the phosphor has an enormous application potential in w-LEDs industry.     

Synthesis,energy transfer mechanism,and tunable emissions of novel Na3La(VO4)2:Re3+ (Re3+ = Dy3+, Eu3+, and Sm3+) vanadate phosphors for near-UV-excited white LEDs

In this study, novel Eu³⁺-, Dy³⁺-, and Sm³⁺-activated Na₃La(VO₄)₂ phosphors were synthesized using a solid state reaction method. X-ray diffraction analysis results indicated that the Na₃La(VO₄)₂ phosphors had an orthorhombic crystal structure with the Pbc21 space group. There were two different La(1)O₈ and La(2)O₈ polyhedra with high asymmetry in the crystal structure. Scanning electron microscopy revealed that the product had a sheet morphology with an irregular particle size. Further, the luminescence properties, including the excitation and emission spectra, and luminescence decay curve, were investigated using a fluorescence spectrometer. The results showed that the Na₃La(VO₄)₂ compound was an excellent host for activating the luminescence of Eu³⁺ (614 nm), Dy³⁺ (575 nm), and Sm³⁺ (647 nm) ions. Further, Dy³⁺/Eu³⁺ co-doped Na₃La(VO₄)₂ phosphors were exploited, and the energy transfer from Dy³⁺ to Eu³⁺ was demonstrated in detail by the photoluminescence excitation, photoluminescence spectra, and luminescent decay curves. The results showed that the energy transfer efficiency from Dy³⁺ to Eu³⁺ was highly efficient, and the energy transfer mechanism was dipole–dipole interactions. Finally, tunable emissions from the yellow region of CIE (0.3925, 0.4243) to the red region of CIE (0.6345, 0.3354) could be realized by rationally controlling the Dy³⁺/Eu³⁺ concentration ratio. These phosphors may be promising materials for the development of solid-state lighting and display systems.     

Synthesis,structure and photoluminescence properties of Tm3+/Dy3+ co-doped borate glass for near-UV white LEDs

Tm³⁺/Dy³⁺ single and co-doped SrO–MgO–B₂O₃ (SMB) glasses were fabricated via the conventional melt-quenching technique. The thermal stability of the host glass was determined by a differential scanning calorimetry (DSC) curve. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were measured to characterize the structural properties and vibration features of the as-prepared glasses, respectively. The transmittances of the studied glasses can reach about 90% in the range from 300 to 800 nm. It can be confirmed that Tm³⁺/Dy³⁺ single and co-doped SMB glasses can all be efficiently excited by near-ultraviolet (NUV) light through absorption and photoluminescence excitation spectra. Moreover, the emission spectra and fluorescence decay curves confirmed the existence of energy transfer between Tm³⁺ and Dy³⁺. The Tm³⁺/Dy³⁺ co-doped glasses can both realize tunable emission from blue light to cool white and eventually to warm white light under the excitation of 352, 362, and 365 nm. Furthermore, by using the Inokuti-Hirayama (I–H) model, the energy transfer is testified to be carried out in Tm³⁺-Dy³⁺ clusters through the dipole-dipole (d-d) interaction mechanism. More importantly, the thermal stability of Tm³⁺/Dy³⁺ co-doped SMB glass was demonstrated by temperature-dependent emission spectra. Overall, these results fully indicate that Tm³⁺/Dy³⁺ co-doped SMB glasses have great potential to be used in NUV-based white light-emitting diodes with different requirements.     

Mn4+-related photoemission enhancement via energy transfer in La2MgGeO6:Dy3+, Mn4+ phosphor for plant growth light-emitting diodes

A double perovskite-type substrate of La₂MgGeO₆ (LMGO) was successfully synthesized via a high-temperature solid-state reaction method and was codoped with Mn⁴⁺ and Dy³⁺ to form a new deep-red phosphor (LMGO:Mn⁴⁺,Dy³⁺) for artificial plant growth light-emitting diodes (LEDs). This extraordinary phosphor can exhibit strong far-red emission with a maximum peak at 708 nm between 650 and 750 nm, which can be ascribed to the ²E_g → ²A_2 g spin-forbidden transition of Mn⁴⁺. The X-ray diffraction (XRD) patterns and high-resolution transmission electron microscopy (HRTEM) clarified that the La³⁺ sites in the host were partly replaced by Dy³⁺ ions. Moreover, we discovered energy transfers from Dy³⁺ to Mn⁴⁺ by directly observing the significant overlap of the excitation spectrum of Mn⁴⁺ and the emission spectrum of Dy³⁺ as well as the systematic relative decline and growth of the emission bands of Dy³⁺ and Mn⁴⁺, respectively. With the increase in the activator (Mn⁴⁺) concentration, the relationship between the luminescence decay time and the energy transfer efficiency of the sensitizer (Dy³⁺) was studied in detail. Finally, an LED device was fabricated using a 460 nm blue chip, and the as-obtained far-red emitting LMGO:Mn⁴⁺,Dy³⁺ phosphors for Wedelia chinensis cultivation. As expected, the as-fabricated plant growth LED-treated Wedelia chinensis cultured in the artificial climate box with overhead LEDs demonstrated that after 28 days of irradiation, the average plant growth rate and the total chlorophyll content were better than those of specimens cultured using the commercial R-B LED lamps, indicating that the as-prepared phosphor could have a potential application in the agricultural industry.     

Luminescence and self-referenced optical temperature sensing performance in Ca2YZr2Al3O12:Bi3+,Eu3+ phosphors

Ca₂YZr₂Al₃O₁₂:Bi³⁺,Eu³⁺ phosphors were elaborated by a traditional solid-state reaction method. The luminescence of Ca₂YZr₂Al₃O₁₂:Bi³⁺ samples, energy transfer from Bi³⁺ to Eu³⁺, and the temperature sensing properties of Ca₂YZr₂Al₃O₁₂:Bi³⁺,Eu³⁺ samples have been systematically researched. Under the excitation of ultraviolet light, Bi³⁺ single doped phosphors give 313 and 392 nm emission bands, which origin from the substitutions of Bi³⁺ instead of Ca²⁺ and Y³⁺ sites, respectively. And the color-adjustable emission from blue to red were observed by increasing Eu³⁺ content in Ca₂YZr₂Al₃O₁₂:Bi³⁺,Eu³⁺ samples. Relying on different temperature dependent variation tendency, the fluorescence intensity ratio (FIR) values present outstanding temperature sensing properties. The absolute and relative sensitivity can be up to 0.826 %K^-1 and 0.664 %K^-1, respectively. All above results suggest that Ca₂YZr₂Al₃O₁₂:Bi³⁺,Eu³⁺ phosphor is a potential alternative for optical thermometer.     

A novel pure red phosphor Ca8MgLu(PO4)7:Eu3+ for near ultraviolet white light-emitting diodes

A novel red-emitting phosphor Ca₈MgLu(PO₄)₇:Eu³⁺ was synthesized by a high-temperature solid-state reaction method. Its crystal structure, photoluminescence emission and excitation spectra, and decay time were investigated in detail. X-ray diffraction (XRD) results indicate that Ca₈MgLu(PO₄)₇ crystallizes in single-phase component with a whitlockite-like structure and the space group R3c of β-Ca₃(PO₄)₂. The emission spectrum shows a dominant peak at 612 nm due to the dipole ⁵D₀→⁷F₂ transition of Eu³⁺, and the luminescence intensity keeps increasing with increasing the content of Eu³⁺ to 100%. The excitation spectrum is coupled well with the emission of near ultraviolet (NUV) LED (380–410 nm). The CIE coordinates of Ca₈MgLu(PO₄)₇:Eu³⁺ phosphor is (0.654, 0.346), being close to the standard value of National Television Standard Committee (NTSC) for red phosphor, (0.670, 0.330). The internal quantum efficiency of the phosphor is 69% under the excitation of 394 nm. The results show that Ca₈MgLu(PO₄)₇:Eu³⁺ is a very appropriate red-emitting phosphor with a high ratio of red and orange for NUV-based white LEDs.     

White emitting Dy3+ activated perovskite titanates and energy transfer by Eu3+ codoping

Perovskite type titanate phosphors Sr_0.97−xDy_0.03Li_xTi_1−xNb_xO₃, Sr_0.9−xDy_xLi_0.1Ti_0.9Nb_0.1O₃ and Sr_0.87−yDy_0.03Eu_yLi_0.1Ti_0.9Nb_0.1O₃ were prepared by conventional solid state method. Herein, white light emission from Sr_0.9−xDy_xLi_0.1Ti_0.9Nb_0.1O₃ phosphors and the lowering of its color temperature through codoping with Eu³⁺ ions are reported. Raman measurements have shown that the incorporation of dopants alters the vibrational properties of these phosphors significantly, indicating the reduction of the local symmetry in the crystal lattice. The addition of LiNbO₃ in SrTiO₃:Dy³⁺ phosphor enhances the luminescence intensity and the yellow to blue ratio resulting in emission of high quality white light with color coordinates corresponding to that of standard white. Life time measurements and data fits of Sr_0.9−xDy_xLi_0.1Ti_0.9Nb_0.1O₃ phosphors revealed the biexponential behaviour of luminescence decay profiles. From Judd-Ofelt analysis it is found that the intensity parameter Ω₂ increases with Dy³⁺ concentration and a quantum efficiency of 90.4% was obtained for optimum concentration. In the case of Dy³⁺ and Eu³⁺ codoped phosphors, the color coordinates are found to be sensitive to the Eu³⁺ concentration and the highest energy transfer efficiency of 92% was obtained for the phosphor doped with 10 mol% Eu³⁺. The emission color changes from cold white to reddish orange when the wavelength of excitation alters from 452 to 388 nm, since the energy transfer mechanism alone take place under 452 nm excitation and both direct absorption and the energy transfer mechanism occurs under 388 nm excitation.     

White light emission from novel host-sensitized single-phase Y2WO6: Ln3+ (Ln3+=Eu3+, Dy3+) phosphors

A series of Eu³⁺- or Dy³⁺-doped and Eu³⁺/Dy³⁺ co-doped Y₂WO₆ in pure phase was synthesized via high-temperature solid-state reaction. X-ray diffraction, diffuse reflection spectra, photoluminescence excitation and emission spectra, the CIE chromaticity coordinates and temperature-dependent emission spectra were exploited to investigate the phosphors. Upon UV excitation at 310 nm, efficient energy transfer from the host Y₂WO₆ to dopant ions in Eu³⁺ or Dy³⁺ single-doped samples was demonstrated and those phosphors were suitable for the UV LED excitation. The intense red emission was observed in Y₂WO₆: Eu³⁺, and blue and yellow ones were observed in Y₂WO₆: Dy³⁺. Concentration quenching in Y₂WO₆: Dy³⁺ phosphors could be attributed to the electric dipole-dipole interaction. In Eu³⁺/Dy³⁺ co-doped Y₂WO₆ phosphors energy transfer process only took place from the host to Eu³⁺/Dy³⁺ ions and warm white-light emission can be obtained by adjusting the dopant concentrations. The temperature-dependent luminescence indicated Eu³⁺/Dy³⁺ co-doped Y₂WO₆ was thermally stable. Our overall results suggested that Y₂WO₆: Ln³⁺ (Ln³⁺=Eu³⁺, Dy³⁺) as warm white-light emitting host-sensitized phosphor might be potentially applied in WLEDs.     

Sr3GdLi(PO4)3F:Eu2+, Mn2+: A tunable blue-white color emitting phosphor via energy transfer for near-UV white LEDs

A series of Eu²⁺ and Mn²⁺ co-doping Sr₃GdLi(PO₄)₃F phosphors have been synthesized through high temperature solid state reaction. Eu²⁺ single doped Sr₃GdLi(PO₄)₃F phosphors have an efficient excitation in the range of 230–430 nm, which is in good agreement with the commercial near-ultraviolet (n-UV) LED chips, and gives intense blue emission centering at 445 nm. The critical distance of the Eu²⁺ ions in Sr₃GdLi(PO₄)₃F is computed and demonstrated that the concentration quenching mechanism of Eu²⁺ is mostly caused by the dipole-dipole interaction. By co-doping Eu²⁺ and Mn²⁺ ions in the Sr₃GdLi(PO₄)₃F host, the energy transfer from Eu²⁺ to Mn²⁺ that can be discovered. With the increase of Mn²⁺ content, emission color can be adjusted from blue to white under excitation of 380 nm, corresponding to chromatic coordinates change from (0.189, 0.108) to (0.319, 0.277). The energy transfer from Eu²⁺ to Mn²⁺ ions is proven to be a dipole-dipole mechanism on the basis of the experimental results and analysis of photoluminescence spectra and decay curves. This study infers that the obtained Sr₃GdLi(PO₄)₃F:Eu²⁺, Mn²⁺ phosphors may be a potential candidate for n-UV LEDs.     

One-step synthesis of Sc2W3O12:Eu3+ phosphors with tunable luminescence for WLED

Sc₂W₃O₁₂ is an important host matrix for rare-earth doped luminescence. However, the conventional method to prepare the material is solid-state reaction, which results into coarse and irregular morphologies. In this work, Eu³⁺ doped Sc₂W₃O₁₂ phosphors with high crystallinity and pure phase were successfully synthesized via one-step hydrothermal method. It was found that the crystalline phase changed from Sc₂W₃O₁₂ phase to Na₄Sc₂(WO₄)₅ phase when the molar ratio between Sc(NO₃)₃ and Na₂WO₄ decreased. The temperature-dependent X-ray diffraction analysis was performed to prove the negative thermal expansion property of Sc₂W₃O₁₂. A systematic study on the effect of reaction time, temperature and Eu³⁺ doping concentration was explored. It was also found that the as-prepared samples displayed tunable emission colors, ranging from blueish white to orange red. Particularly, the white light emission with the chromaticity coordinate of (0.3395, 0.3289) can be realized in Sc₂W₃O₁₂: 5% Eu³⁺. What's more, the photoluminescence properties of the samples were investigated under different ambient temperatures between 97 and 280?K. The result clearly showed energy transfer between Eu³⁺ and WO₄^2?. The above results suggested that Sc₂W₃O₁₂:Eu³⁺ can be excellent candidate for solid-state lasing, panel display and WLEDs.     

Spectroscopic characterizations and investigation of Judd-Ofelt intensity parameters of Dy3+-doped Ba2La8(SiO4)6O2 near white light emitting phosphor

A series of Dy³⁺-activated Ba₂La₈(SiO₄)₆O₂ phosphors were synthesized using the solid-state method with the objective of developing single host white light emitting phosphors for use in solid state lighting applications. The Dy³⁺ concentration varied between 0.01 and 0.05 mol%. The as-prepared phosphors crystal structure, optical, and photoluminescent properties (PL), along with energy transfer mechanism and luminescence decay, were investigated. The production of a single-phase Ba₂La₈(SiO₄)₆O₂ with hexagonal symmetry was verified by the findings of the X-ray diffraction analysis. When the Ba₂La₈(SiO₄)₆O₂: Dy³⁺ phosphors are exposed to ultraviolet light, they emit the characteristic yellow PL emissions caused by the ⁴F_9/2 → ⁶H_13/2 transition. The Judd-Ofelt (J-O) parameters (Ω₂, Ω₄, Ω₆) were computed using the excitation spectra. The characteristics of the Dy³⁺ transition indicate that the asymmetric environment around the ligand was suggested by the trend, which was followed by J-O parameters. Due to the dominance of the electric-dipole transition in the luminescence spectrum, the Ba₂La₈(SiO₄)₆O₂:0.03Dy³⁺ phosphor displayed yellowish white emission with CIE coordinates of (0.358, 0.398) and a CCT of 4724 K. The synthesized phosphor may be a useful material in the fabrication of white-emitting phosphor for LEDs application.     

Tunable emission of single-phased NaY(WO4)2:Sm3+ phosphor based on energy transfer

A series of NaY(WO₄)₂:Sm³⁺ phosphors were prepared by high temperature solid state reaction. When excited by ultraviolet and blue light, their emission spectra cover entirely visible light region, due to intrinsic luminescence of WO₄^2- group as well as Sm³⁺ 4f-4f transitions. White light emission was obtained from NaY_0.99Sm_0.01(WO₄)₂ phosphor under radiation of 265 nm UV light, and intense yellow and red emission from ⁶H_{J(J=5/2, 7/2, 9/2)} transitions were observed when pumped Sm^{3+ 4}G_5/2 by 405 nm blue light. With incorporation of Sm³⁺ into NaY(WO₄)₂ host, higher-level emission from Sm³⁺ at 650 nm was generated by energy transfer from WO₄^2- to Sm³⁺ under excitation of 265 nm. The corresponding energy transfer mechanism was demonstrated to be a dipole-dipole interaction. In addition, tunable emission from blue to white and, finally, to red was realized by increasing Sm³⁺ doping concentration. The band gap of NaY(WO₄)₂ calculated from diffuse reflection spectra indicates a semiconducting character. All these results show that NaY_1−xSm_x(WO₄)₂ phosphor provides promising application for conversion of frequencies emitted by UV or blue LEDs.