Tunable luminescence properties and energy transfer of single-phase Ca<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>O: Dy<Superscript>3+</Superscript>, Eu<Superscript>2+</Superscript> multi-color phosphors for warm white light

The novel Ca_4?x(PO₄)₂O: xDy³⁺ and Ca_4?x?y(PO₄)₂O: xDy³⁺, yEu²⁺ multi-color phosphors were synthesized by traditional solid-state reaction. The crystal structure, particle morphology, photoluminescence properties and energy transfer process were investigated in detail. The X-ray diffraction (XRD) results demonstrate that the products showed pure monoclinic phase of Ca₄(PO₄)₂O when x < 0.1. The scanning electron microscopy (SEM) indicated that the phosphors were grain-like morphologies with diameters of ~ 3.7–7.0 μm. Under excitation of 345 nm, Dy³⁺-doped Ca₄(PO₄)₂O phosphors showed multi-color emission bands at 410, 481 and 580 nm originated from oxygen vacancies and Dy³⁺. Interestingly, Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors exhibited blue emission band at 481 nm and broad emission band from 530 to 670 nm covering green to red regions. The energy transfer process from Dy³⁺ to Eu²⁺ was observed for the co-doped samples, and the energy transfer efficiency reached to 60% when Eu²⁺ molar concentration was 8%. In particular, warm/cool/day white light with adjustable CCT (2800–6700 K) and high CRI (R_a > 85) can be obtained by changing the Eu²⁺ co-doping contents in Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors. The optimized Ca_3.952(PO₄)₂O: 0.04Dy³⁺, 0.008Eu²⁺ phosphor can achieve the typical white light with CCT of 4735 K and CRI of 87.     

Hydrothermal synthesis of NaLa(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Eu<Superscript>3+</Superscript> octahedrons and tunable luminescence by changing Eu<Superscript>3+</Superscript> concentration and excitation wavelength

NaLa(WO₄)₂:Eu³⁺ phosphors with different Eu³⁺ concentrations have been synthesized by a hydrothermal method. The phase is confirmed by XRD analysis, which shows a pure-phase NaLa(WO₄)₂ XRD pattern for all of NaLa(WO₄)₂:Eu³⁺ phosphors. The SEM and TEM images indicate that all of NaLa(WO₄)₂:Eu³⁺ phosphors have a octahedral morphology. These suggest that the Eu³⁺ doping has no influence on the structure and growth of NaLa(WO₄)₄ particles. By monitoring the emission of Eu³⁺ at 615 nm, NaLa(WO₄)₂:Eu³⁺ phosphors show excitation bands originating from both host and Eu³⁺ ions. Under the excitation at 271 nm corresponding to WO₄ ^2? groups, emission bands coming from the ¹A₁ → ³T₁ transition with the WO₄ ^2? groups and the ⁵D₀ → ⁷F_j (j = 0, 1, 2, 3 and 4) transitions of Eu³⁺ are observed. The emission intensity relating to WO₄ ^2? groups decreases with increasing Eu³⁺ concentration. But emission intensities of Eu³⁺ increase firstly and then decreases because of concentration quenching effect. Under the excitation at 395 nm corresponding to ⁷F₀ → ⁵L₆ transition of Eu³⁺, only characteristic Eu³⁺ emission bands can be observed. The results of this work suggest that tunable luminescence can be obtained for Eu³⁺ doped NaLa(WO₄)₂ phosphors by changing Eu³⁺ concentration and excitation wavelength.     

Sr<Subscript>3</Subscript>GdLi(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F: Sm<Superscript>3+</Superscript> phosphor: preparation and luminescence properties evaluation

A series of Sr₃Gd_1?xLi(PO₄)₃F: xSm³⁺ (x?=?0.02, 0.04, 0.06, 0.08) phosphors were synthesized by a high-temperature solid state method. The Sm³⁺ activated Sr₃GdLi(PO₄)₃F phosphors can be efficiently excited by the wavelengths in the range from 350 to 450 nm, which matches perfectly with that of the commercial near-UV LED chips. The optimal doping concentration of Sr₃Gd_1?xLi(PO₄)₃F: xSm³⁺ phosphors was determined to be x?=?0.04, corresponding to the quantum efficiency of 2.23%, and the CIE chromaticity coordinates (x?=?0.5172, y?=?0.4641). The concentration quenching mechanism of Sm³⁺ in Sr₃GdLi(PO₄)₃F host is mainly attributed to the dipole–dipole interaction, which was confirmed by the fluorescent lifetimes. The effect of temperature on the photoluminescence property of Sr₃GdLi(PO₄)₃F: Sm³⁺ was investigated. 90% of the intensity is preserved at 150 °C. In addition, a white light emitting diode (WLED) lamp was fabricated by a 405 nm n-UV LED chip coated with Sr₃Gd_0.96Li(PO₄)₃F:0.04Sm³⁺ phosphor and commercial yellow phosphor (YAG: Ce³⁺) of a certain mass ratio. The present work indicates that the Sr₃GdLi(PO₄)₃F: Sm³⁺ orange–red-emitting phosphors tend to be potential application in n-UV WLED.     

Influence of Mn<Superscript>2+</Superscript> on the up-conversion emission performance of Mn<Superscript>2+</Superscript>, Yb<Superscript>3+</Superscript>, Er<Superscript>3+</Superscript>: ZnWO<Subscript>4</Subscript> green phosphors

The Mn²⁺, Yb³⁺, Er³⁺: ZnWO₄ green phosphors are synthesized successfully through the high temperature solid state reaction method. The micro-structure and morphology have been investigated by means of XRD and EDS. The doped concentrations of Mn²⁺, Yb³⁺, Er³⁺ are measured by ICP. The absorption spectra and emission spectra with different doped concentrations of Mn²⁺ are presented to reveal the influence of Mn²⁺ on the green up-conversion performance. Excited with 970 nm LED, the up-conversion emission peak at 547 nm is obtained and the CIE spectra as well as the green light photo are also presented. The results indicate that the Mn²⁺ ions play the role of the luminescence adjustment in the up-conversion process, which can improve the up-conversion green emission intensity effectively. The luminescence adjustment mechanism of Mn²⁺ ions in Mn²⁺, Yb³⁺, Er³⁺: ZnWO₄ green phosphors has been discussed. The crystal parameters of Dq, B and C are calculated to evaluate the energy level split effect.     

Persistent luminescence of Zn<Subscript>2</Subscript>GeO<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript>/Pr<Superscript>3+</Superscript> phosphors

Zn₂GeO₄, Zn₂GeO₄:Mn²⁺, Zn₂GeO₄:Pr³⁺ and Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors were fabricated by a solid state reaction. The phase and luminescent properties of the fabricated phosphors were investigated. The XRD patterns show that all of the fabricated phosphors have an orthorhombic structure. The fabricated Zn₂GeO₄ shows an emission band in the range of 350–550 nm. The fabricated Zn₂GeO₄:Mn²⁺ and Zn₂GeO₄:Pr³⁺ phosphors show emission bands corresponding to Mn²⁺ and Pr³⁺ ions, respectively. The fabricated Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor shows the emission band results from Mn²⁺ and the codoped Pr³⁺ enhances the emission intensity of Mn²⁺. Moreover, Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor exhibits longer decay time than that of Zn₂GeO₄:Mn²⁺. The higher intensity and longer lifetime of Mn²⁺ emission are induced by the energy transfer from Pr³⁺ of various vacancies to Mn²⁺ in Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors.     

Optical properties of Eu<Superscript>3+</Superscript> activated SrLa<Subscript>2</Subscript>O<Subscript>4</Subscript> red-emitting phosphors for WLED applications

The SrLa_2?xO₄:xEu³⁺ phosphors are synthesized through high-temperature solid-state reaction method at 1473 K with various doping concentration. Their phase structures, absorption spectra, and luminescence properties are investigated by X-ray diffraction (XRD), UV–Vis spectrophotometer and photoluminescence spectrometry. The intense absorption of SrLa_2?xO₄:xEu³⁺ phosphors have occurred around 400 nm. The prominent luminescence spectra of the prepared phosphors exhibited bright red emission at 626 nm. The doping concentration 0.12 mol% of Eu³⁺ is shown to be optimal for prominent red emission and chromaticity coordinates are x?=?0.692, y?=?0.3072. Considering the high colour purity and appropriate emission intensity of Eu³⁺ doped SrLa₂O₄ can be used as red phosphors for white light emitting diodes (WLEDs).     

Crystal structure and luminescence property of a single-phase white light emission phosphor Sr<Subscript>3</Subscript>YNa(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F:Dy<Superscript>3+</Superscript>

A series of single-phase Sr₃YNa(PO₄)₃F:Dy³⁺ phosphors were successfully synthesized via a conventional solid state reaction process. The powder X-ray diffraction patterns were utilized to confirm the phase composite and crystal structure. The phosphor could be excited by the ultraviolet visible light in the region from 300 to 420 nm, and it shown two dominant emission bands peaking at 484 nm (blue light) and 580 nm (yellow light) which originated from the transitions of ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 of Dy³⁺, respectively. The optimum dopant concentration of Dy³⁺ ions was confirmed to be 7 mol% in Sr₃YNa(PO₄)₃F:Dy³⁺ system and the concentration quenching mechanism is dipole–dipole interaction. The lifetime values of Dy³⁺ ions at different concentrations (x?=?0.03, 0.05, 0.07, 0.09 and 0.11) were determined to be about 0.855, 0.759, 0.686, 0.606 and 0.546 ms, respectively. The thermal stability of luminescence of Sr₃YNa(PO₄)₃F:0.07Dy³⁺ phosphor was also investigated and the activated energy was deduced to be 0.228 eV, which shows good thermal stability. The chromaticity coordinates fall in the white-light region calculated by the emission spectrum. These results show that Sr₃YNa(PO₄)₃F:Dy³⁺ phosphor can be a promising white emitting phosphor for white LEDs.     

Rapid synthesis and enhancement in down conversion emission properties of BaAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>,RE<Superscript>3+</Superscript> (RE<Superscript>3+</Superscript>=Y,Pr) nanophosphors

BaAl₂O₄:Eu²⁺,RE³⁺ (RE³⁺=Y, Pr) down conversion nanophosphors were prepared at 600 °C by a rapid gel combustion technique in presence of air using boron as flux and urea as a fuel. A comparative study of the prepared materials was carried out with and without the addition of boric acid. The boric acid was playing the important role of flux and reducer simultaneously. The peaks available in the XPS spectra of BaAl₂O₄:Eu²⁺ at 1126.5 and 1154.8 eV was ascribed to Eu²⁺(3d _5/2) and Eu²⁺(3d _3/2) respectively which confirmed the presence of Eu²⁺ ion in the prepared lattice. Morphology of phosphors was characterized by tunneling electron microscopy. XRD patterns revealed a dominant phase characteristics of hexagonal BaAl₂O₄ compound and the presence of dopants having unrecognizable effects on basic crystal structure of BaAl₂O₄. The addition of boric acid showed a remarkable change in luminescence properties and crystal size of nanophosphors. The emission spectra of phosphors had a broad band with maximum at 490–495 nm due to electron transition from 4f ⁶5d ¹ → 4f ⁷ of Eu²⁺ ion. The codoping of the rare earth (RE³⁺=Y, Pr) ions help in the enhancement of their luminescent properties. The prepared phosphors had brilliant optoelectronic properties that can be properly used for solid state display device applications.     

Sr3Bi(PO4)3:Eu2+, Mn2+: Single-phase and color-tunable phosphors for white-light LEDs

Sr₃Bi(PO₄)₃:Eu²⁺, Sr₃Bi(PO₄)₃:Mn²⁺, and Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ phosphors were synthesized by solid state reaction. The structure and luminescent characteristics were investigated by X-ray powder diffraction and fluorescent spectrophotometer. All samples have the structural type of eulytine. The excitation and emission spectra of Sr₃Bi(PO₄)₃:0.01Eu²⁺ sample show characteristic bands of Eu²⁺ ions. Also, the excitation and emission spectra of Sr₃Bi(PO₄)₃:0.06Mn²⁺ sample show characteristic bands of Mn²⁺ ions. The emission color of Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ sample could be tuned through tuning the co-dopant concentration of Mn²⁺ ions. The decay times for the Eu²⁺ ions decrease with the increase of Mn²⁺ dopant concentration, but the energy transfer efficiency increases with the increase of Mn²⁺ dopant concentration. On the basis of the luminescent spectra and fluorescence decay curves, we confirm that the energy transfer process from the Eu²⁺ to Mn²⁺ ions takes place in the co-doped Sr₃Bi(PO₄)₃ phosphor. Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ sample shows the good thermostability. The emission intensity of the sample at 400 K is about 60% of the value at 300 K. These results show Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ phosphors could be anticipated for UV-pumped white-light-emitting diodes.     

Synthesis and characterizations of Dy3+ doped Sr3Al2O6:Eu2+ powder phosphors through citric acid precursor

Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors were synthesized by the polymer precursor method. The X-ray powder diffraction patterns show that the samples have a cubic structure with a space group of Pa3. In the excitation spectrum, the phosphors show a wide absorption in the UV region from 250 to 450 nm, which corresponds to the crystal field splitting of the Eu²⁺ d-orbital. All the emission spectrum of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors show the broad band emission peaked at about 518 nm, which can be ascribed to the typical 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺ ions. And the best dopant concentration of Dy³⁺ ions for Sr₃Al₂O₆:2 mol%Eu²⁺, xDy³⁺ phosphors is 2 mol%. The excitation wavelengths have no influences on emission peaks, but have clear influences on emission intensities.     

Photoluminescence properties of a novel red-emitting phosphor Ba<Subscript>2</Subscript>LaV<Subscript>3</Subscript>O<Subscript>11</Subscript>:Eu<Superscript>3+</Superscript>

Ba₂LaV₃O₁₁:Eu³⁺ phosphors were firstly synthesized by the traditional solid-state reaction method at 1100 °C. Their luminescence properties were investigated by photoluminescence excitation and emission spectra. The excitation spectrum shows a broad band centered at about 275 nm in the region from 200 to 370 nm, which is attributed to an overlap of the charge transfer transitions of O^2??→?V⁵⁺ and O^2??→?Eu³⁺. The phosphors exhibit the red emissions of Eu³⁺ and the emission intensity ratio of ⁵D₀?→?⁷F₂ to ⁵D₀?→?⁷F₁ is dependent on the Eu³⁺ concentration due to an environment change about Eu³⁺ ions. Concentration quenching occurs at 30 mol% in the phosphors and exchange interaction is its main mechanism. Ba₂LaV₃O₁₁:Eu³⁺ displays tunable CIE color coordinates from yellow orange to red depended on Eu³⁺ content, which may have a potential application for illuminating and display devices.     

Roles of doping ions in persistent luminescence of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>, RE<Superscript>3+</Superscript> phosphors

The polycrystalline Eu²⁺ and RE³⁺ co-doped strontium aluminates SrAl₂O₄:Eu²⁺, RE³⁺ were prepared by solid state reactions. The UV-excited photoluminescence, persistent luminescence and thermo-luminescence of the SrAl₂O₄:Eu²⁺, RE³⁺ phosphors with different composition and doping ions were studied and compared. The results showed that the doped Eu²⁺ ion in SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors works as not only the UV-excited luminescent center but also the persistent luminescent center. The doped Dy³⁺ ion can hardly yield any luminescence under UV-excitation, but can form a electron trap with appropriate depth and greatly enhance the persistent luminescence and thermo-luminescence of SrAl₂O₄:Eu²⁺. Different co-doping RE³⁺ ions showed different effects on persistent luminescence. Only the RE³⁺ ion (e.g. Dy³⁺, Nd³⁺), which has a suitable optical electro-negativity, can form the appropriate electron trap and greatly improve the persistent luminescence of SrAl₂O₄:Eu²⁺. Based on above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated.     

Luminescence properties and energy transfer of co-doped Ba<Subscript>3</Subscript>GdNa(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F:Ce<Superscript>3+</Superscript>,Tb<Superscript>3+</Superscript> green-emitting phosphors

Phase pure Ce³⁺ and Tb³⁺ singly doped and Ce³⁺/Tb³⁺ co-doped Ba₃GdNa(PO₄)₃F samples have been synthesized via the high temperature solid-state reaction. The crystal structures, photoluminescence properties, fluorescence lifetimes, thermal properties and energy transfer of Ba₃GdNa(PO₄)₃F:Ce³⁺,Tb³⁺ were systematically investigated. Rietveld structure refinement indicates that Ba₃GdNa(PO₄)₃F crystallizes in a hexagonal crystal system with the space group P-6. For the co-doped Ba₃GdNa(PO₄)₃F:Ce³⁺,Tb³⁺ samples, the emission color can be tuned from blue to green by varying the doping concentration of the Tb³⁺ ions. The intense green emission was realized in the Ba₃GdNa(PO₄)₃F:Ce³⁺,Tb³⁺ phosphors on the basis of the highly efficient energy transfer from Ce³⁺ to Tb³⁺. Also the energy transfer mechanism has been confirmed to be quadrupole–quadrupole interaction, which can be validated via the agreement of critical distances obtained from the concentration quenching (13.84 Å). These results show that the developed phosphors may possess potential applications in near-ultraviolet pumped white light-emitting diodes.     

Synthesis,tunable luminescence and thermal stability of Mg<Subscript>2</Subscript>Al<Subscript>4</Subscript>Si<Subscript>5</Subscript>O<Subscript>18</Subscript>:Ce<Superscript>3+</Superscript>/Mn<Superscript>2+</Superscript> phosphors

Ce³⁺/Mn²⁺ singly doped and codoped Mg₂Al₄Si₅O₁₈ phosphors were synthesized by a solid state reaction. The phase, luminescent properties and thermal stability of the synthesized phosphors were investigated. Ce³⁺ and Mn²⁺ singly doped Mg₂Al₄Si₅O₁₈ phosphors show emission bands locating in blue and yellow–red regions, respectively. In Ce³⁺ and Mn²⁺ codoped Mg₂Al₄Si₅O₁₈, tunable luminescence was obtained because of the energy transfer from Ce³⁺ to Mn²⁺. In Mg₂Al₄Si₅O₁₈:Ce³⁺/Mn²⁺ phosphors with a fixed Ce³⁺ concentration, energy transfer efficiency increases with the increasing Mn²⁺ concentration, which is confirmed by the continually decreasing intensity and shortening decay time of Ce³⁺ emission. Moreover, the luminescent properties and thermal stability provide a great significance on the applications in the field of light emitting diodes.     

Enhanced red-emitting phosphor Na<Subscript>2</Subscript>Ca<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript>:Eu<Superscript>3+</Superscript> by charge compensation

A series of novel red-emitting Na₂Ca_3???x Si₂O₈:xEu³⁺ phosphors were synthesized by solid state reactions. The phosphors can strongly absorb 395 nm light, and show red emission with a good color purity. The excitation and emission spectra properties of Na₂Ca₃Si₂O₈:Eu³⁺ were characterized. Na₂Ca₃Si₂O₈:Eu³⁺ with self-compensated and alkali metal ions charge compensated approaches (2Ca²⁺→Eu³⁺ + M⁺, M?=?Li⁺, Na⁺, K⁺) have investigated, which found that the red emission of luminescent intensity can be greatly enhanced, and shows superior luminescent property to the commercial Y₂0₃S:Eu³⁺. The present work implies that the efficient charge compensated phosphors are promising candidates as red-emitting phosphor for w-LEDs.     

Structural and optical characterization of RE (Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) doped SrMg<Subscript>2</Subscript>Al<Subscript>6</Subscript>Si<Subscript>9</Subscript>O<Subscript>30</Subscript> nanocrystalline phosphor

This article present the reports on optical study of Eu²⁺ and Ce³⁺ doped SrMg₂Al₆Si₉O₃₀ phosphors, which has been synthesized by combustion method at 550 °C. Here SrMg₂Al₆Si₉O₃₀:Eu²⁺ emission band observed at 425 nm by keeping the excitation wavelength constant at 342 nm, whereas SrMg₂Al₆Si₉O₃₀:Ce³⁺ ions shows the broad emission band at 383 nm, under 321 nm excitation wavelength, both the emission bands are assigned due to 5d–4f transition respectively. Further, phase purity, morphology and crystallite size are confirmed by XRD, SEM and TEM analysis. However, the TGA analysis is carried out to know the amount of weight lost during the thermal processing. The CIE coordinates of SrMg₂Al₆Si₉O₃₀:Eu²⁺ phosphor is observed at x?=?0.160, y?=?0.102 respectively, which may be used as a blue component for NUV-WLEDs. The critical distance of energy transfer between Ce³⁺ ions and host lattice is found to be 10.65 Å.     

Synthesis and annealing effects on the optical spectroscopy properties of red-emitting Gd(P<Subscript>0.5</Subscript>V<Subscript>0.5</Subscript>)O<Subscript>4</Subscript>: x at.% Eu<Superscript>3+</Superscript>

In this work, Gd(P_0.5V_0.5)O₄: x at.% Eu³⁺ phosphors with different dopant concentrations (x?=?1, 3, 5, 6, 7, 9) were synthesized through chemical coprecipitation method. The phosphors were characterized by XRD, SEM, infrared spectroscopy, photoluminescence excitation, emission spectra and CIE. The results of XRD indicate that the obtained phosphors have the tetragonal phase structure. Eu³⁺ emission transitions arise mainly from the ⁵D₀ level to the ⁷F_J (J?=?0, 1, 2, 3, 4) manifolds. The emission intensity and crystalline of Gd(P_0.5V_0.5)O₄:x at% Eu³⁺ powders are increasing with annealing temperature at 600, 800, 1000, 1100, and 1200 °C, respectively. The introduction of VO₄^3? can broaden the range of UV excitation spectrum wavelength and enhance the transition between ⁵D₀ → ⁷F₁ to ⁵D₀ → ⁷F₂ for long wavelength emission. And the most dominant emission peak of Eu³⁺ for ⁵D₀ → ⁷F₂ transition is closer to pure red light at 622 nm. The maximum emission intensity of the phosphors is the concentration of 6 at.% Eu³⁺ because of the distance of the neighbor Eu³⁺ ions reaching a certain critical value and the influence of multipolar interaction. Compared to commercial phosphors Y₂O₃:Eu³⁺ and (Y,Gd)BO₃:Eu³⁺, our work yielded a longer wavelength red light emission intensity and a higher proportion of red light to orange light. All our results indicate that color purity of this phosphor turns it into a promising red phosphor in ultraviolet-pumped light-emitting diodes.     

Synthesis,structure and photoluminescence properties of (Sr,Ca)AlSiN<Subscript>3</Subscript>:Eu<Superscript>2+</Superscript> phosphor for white light emitting diodes with controllable optical performance

A series of Sr_yCa_1?x?yAlSiN₃:xEu²⁺ (x = 0–0.01, y = 0–0.8) phosphors have been successfully prepared by solid state reaction under atmospheric pressure. All the phosphors exhibit orthorhombic crystal structure similar with CaAlSiN₃ structure. It is found that the emission bands for all Ca_1?xAlSiN₃:xEu²⁺ phosphors are centered at ~650 nm and fluorescence quenching has been observed along with the increase of Eu²⁺ concentration in host materials. Through substitution of Ca²⁺ by Sr²⁺, an expected red emission peak (625 nm) and enhanced luminescent intensity can be achieved. The obtained Sr_0.8Ca_0.192AlSiN₃:0.008Eu²⁺ phosphor was further used as efficient red component to fabricate white light emitting diodes (LEDs). Under the optimized condition of LED packaging, the white LEDs own the excellent optical properties with luminous efficiency of 90.6 lm/W and an ideal color rendering index (Ra = 82). Furthermore, the color correlated temperature of white LEDs can be simply adjusted through changing the red phosphor concentration and dispensing package saves time.     

Luminescence studies on Eu<Superscript>2+</Superscript> and Tb<Superscript>3+</Superscript> doped Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript> phosphors

Eu²⁺ and Tb³⁺ doped Ca₂MgSi₂O₇ phosphors were synthesized by conventional solid-state reaction. The phase formation was confirmed by X-ray powder diffraction technique and refined lattice parameters were calculated by rietveld refinement process using Celref v3. The photoluminescence (PL) excitation and emission spectra were investigated. The phosphors exhibited broaden green emitting luminescence peaking at 520 nm when excited at 374 nm source. Morphological studies were carried out using Scanning electron microscopy (SEM) images of the sample with optimum PL emission. The dependence of photoluminescence intensity on co-dopant concentration and the kinetic parameters were also reported. Time resolved fluorescence spectroscopy (TRFS) is used to investigate the decay in luminescence signals with respect to time. The sample proved to be a good long lasting material, which makes it useful in emergency signs, textile printing, textile exit sign boards and electronic instrument dial pads etc.     

Synthesis,photoluminescence properties of Sr<Subscript>1.95</Subscript>Ba<Subscript>0.05</Subscript>CeO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> for LED applications

The Sr_1.95Ba_0.05 CeO₄:Eu³⁺ phosphors are synthesized by the solid-state reaction method. The samples are characterized using X-ray diffraction (XRD), diffuse reflectance spectroscopy and photoluminescence (PL) spectra. The XRD results reveal that the synthesized phosphors are genuine crystalline and belong to the orthorhombic structure. The intense PL emission is optimized from the PL spectra at various doping concentrations of europium ions. The results indicates that the phosphor can be effectively excited under 264 nm wavelength producing on intense emission spectrum of the synthesis material at 484 nm (blue region). The color purity of the phosphor is confirmed by CIE coordinates (x = 0.217, y = 0.265). The experimental data indicate that the prepared phosphors can be used as blue-emitting material in the field of illuminations and display devices.