Luminescence of YAl3 (BO3)4: Eu2+, Dy3+ phosphor and its luminescence decay characteristics

Eu²⁺, Dy³⁺ co-doped YAl₃ (BO₃)₄ phosphors are synthesized by sol-gel method. The phosphors show prominent blue luminescence due to the 4f⁷–4f⁶5d transition of Eu²⁺. The emission intensity is greatly improved when Dy³⁺ is doped into the YAl₃ (BO₃)₄:Eu²⁺ system. The 1% Dy³⁺ in Eu²⁺, Dy³⁺ co-doped YAl₃ (BO₃)₄ phosphors is the optimum doping concentration. The luminescence decay characteristics of the samples have also been investigated, exhibiting the decay times of approximately 0.1 μs, which is much shorter compare to other Eu²⁺ doped phosphors.     

Structures and luminescence properties of Eu2+- doped α-sialon phosphors for UV-LED

Eu²⁺-doped α-sialon phosphor was synthesized and structures and various luminescence properties were studied. High crystalline Ca_0.8Al_2.8Si_9.2O_1.169N_14.94 phase was successively obtained for undoped and Eu²⁺-doped samples. Eu²⁺-doped α-sialon phosphor exhibited wide absorption in ultra violet (UV) and visible range, and high broad emission band peaking at from 570 to 582 nm. The optimum compositions and process conditions was obtained from 0.75 mol% Eu²⁺–doped Ca_0.8Al_2.8Si_9.2O_1.169N_14.94 fired at 1650 °C for 2 h in 30% H₂–70% N₂ atm. In addition, fabrication of UV-light emitting diode (LED) lamp using this phosphor was conducted and the optical properties were measured. Relative quantum efficiency of the phosphor and luminous efficiency of the lamp were 83.66% and 35.28 lm/W, respectively. Those results indicated that Eu²⁺-doped α-sialon phosphor in this study was a good candidate for UV-LED light source.     

白光LED用氮（氧）化物荧光粉研究进展

综述了近年来氮（氧）化物荧光粉的制备方法、品格结构、发光性质及其在白光LED中的应用情况。此类荧光粉因其结构的多样性和电子云扩大效应的影响,一般在紫外-蓝光区具有高的吸收效率,并且随着基质和激活离子的改变,发射光谱可覆盖整个可见光区域,适用于制造白光LED。利用氮（氧）化物荧光粉封装的白光LED具有色温可调性强、发光效率高、色坐标稳定性好、显色指数高等优点。最后提出了氮（氧）化物荧光粉研究中尚未解决的问题.     

Photoluminescence properties of Y2O3co-doped with Eu and Bi compounds as red-emitting phosphor for white LED

Bismuth doped Y₂O₃: Eu was used as a red phosphor with a very high efficiency and an appropriate emission wavelength of around 310–400 nm. This red phosphor was synthesized by the solid state reaction which is normally used in the field of white LEDs. In this study, we synthesized Y₂O₃: Eu, Bi phosphors using a solid state reaction. We investigated the effect of the Eu^{3 +} and Bi^{3 +} concentrations and additive fluxes on the emission characteristics. The fabricated phosphors were investigated by analyzing their particle size and crystal structure with scanning electron microscopy and X-ray diffraction (XRD). Their photoluminescence (PL) spectra were also measured at room temperature.     

白光LED用几种Eu^2＋激活的红色荧光体的性能

本文对固态照明白光LED用Eu^2＋激活硫化钙、Eu^2＋激活的氮化物和氮氧化物三种高效红色荧光体的物理化学和发光特性进行对比和分析。氮（氧）化物红色荧光体的性能稳定。四种材料适合用作InGaN蓝光LED光转换红色荧光体,和YAG：Ce黄粉组合,使制作的白光LED的显色指数Ra大大提高,有利实现LED普通照明。     

Luminescent properties of Sr2ZnSi2O7: Eu2+ phosphors prepared by combustion-assisted synthesis method

A blue-emitting phosphor Sr₂ZnSi₂O₇: Eu²⁺ was prepared by combustion-assisted synthesis method and an efficient blue emission under from ultraviolet to visible light was observed. The emission spectrum shows a single intensive band centered at 475?nm, which corresponds to the 4f⁶5d¹??4f⁷ transitions of Eu²⁺. The excitation spectrum is a broad band extending from 250 to 450?nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The effect of doped Eu²⁺ concentration on the emission intensity of Sr₂ZnSi₂O₇: Eu²⁺ was also investigated and the corresponding concentration quenching mechanism is verified to be an electric multipole-multipole interaction.     

Synthesis and temperature-dependent optical properties of Eu3+-doped NaYSiO4 red-emitting phosphors

Abstract

Novel Eu³⁺-activated orthosilicate NaYSiO₄:xEu³⁺ (x?=?0.02, 0.05, and 0.20) red-emitting phosphors were developed for white light emitting diode applications. The X-ray diffraction (XRD), photoluminescence excitation and emission spectra, temperature-dependent curves were applied to characterize the samples. The red emission of the NaYSiO₄:Eu³⁺ phosphor corresponding to ⁵D₀→⁷F₂ (614?nm) transition was observed under the excitation of 394?nm wavelength, which is suitable for UV LED chip. The quenching temperature for NaYSiO₄:0.05Eu³⁺ was found to be over 500 K. The CIE chromaticity coordinates of NaYSiO₄:0.05Eu³⁺ are very close to the National Television System Committee (NTSC) standard red.     

Sol-gel Synthesis and Photoluminescence Characterization of Ba2SiO4:Eu2+ Green Phosphors for White-LED Application

In this paper, Ba₂SiO₄:Eu²⁺ green phosphor was synthesized by sol-gel method. TGA-DTA, XRD, SEM and PL spectra were used to characterize the as-prepared phosphors. The phosphors are composed of nanoparticles with 60 nm grain size and exhibit green light with a broad peak around 500 nm. The relationship between crystal growth, morphology and luminescent properties was studied. The structure and luminescence properties of phosphors synthesized in different conditions were also discussed.     

Morphology and luminescence properties of BaMgAl10O17:Eu2+ blue phosphors by Aerosol Flame Deposition

BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu) is widely used as a blue phosphor for fluorescent lamps and plasma display panels (PDP). The improvement of the luminescence efficiency is a significant issue for applications in plasma display panels. In this study, the Aerosol Flame Deposition (AFD) was applied to fabricate BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu) particles with spherical shape and fine size in order to improve their luminescence. The sub-micrometer powder was synthesized in spherical shape in an oxy-hydrogen flame and deposited on a substrate in the form of porous film. The particle size of as-prepared powder increased with increasing the concentration of precursor solution and the heat treatment under reducing atmosphere increased particle size additionally with surface roughening due to the needle-like crystallized phases. Photoluminescence spectrum was observed at about 450nm due to the 5d–4f transition of Eu²⁺ and the intensity of phosphor was as high as 70% of that of the commercial phosphor.     

Photoluminescence properties of a green to red-emitting Eu3+, Tb3+ co-doped CaBi2Ta2O9 ferroelectrics

The CaBi₂Ta₂O₉ bismuth layered-structure ferroelectrics doped with rare earth ions Eu³⁺ and Tb³⁺, or co-doped with Eu³⁺/Tb³⁺ were prepared by the conventional solid-state reaction method. The microstructure and photoluminescence properties of CaBi₂Ta₂O₉: Eu³⁺, CaBi₂Ta₂O₉: Tb³⁺ and CaBi₂Ta₂O₉: Eu³⁺/Tb³⁺ were investigated. The XRD patterns demonstrate that the rare earth ions have been effectively doped into CaBi₂Ta₂O₉ host lattices. The photoluminescence properties of CaBi₂Ta₂O₉ with different activator ions are researched in details. The novel red and green light emissions were observed under the excitation of blue and near-UV light. Notably, tunable emissions and a warm-white color have been achieved in the Eu³⁺ and Tb³⁺ co-doped CaBi₂Ta₂O₉ powders. These results suggest that CaBi₂Ta₂O₉: Eu³⁺, CaBi₂Ta₂O₉: Tb³⁺ and CaBi₂Ta₂O₉: Eu³⁺/Tb³⁺ could be novel luminescence materials. It is also expected that rare earth doped CaBi₂Ta₂O₉ ferroelectrics can find potential applications in new multifunctional photoluminescence ferroelectric devices.     

Deposition of Europium Oxide on Si and its optical properties depending on thermal annealing conditions

We investigate the influence of the ambient gas during thermal annealing on the photoluminescence (PL) properties of europium compound thin films on Si substrates. The films were deposited by radio-frequency magnetron sputtering and subsequently annealed in N₂ or O₂ ambient gas by rapid thermal annealing (RTA). The results of X-ray diffraction indicate that the resulting europium compound annealed in N₂ ambient have several silicate phases such as EuSiO₃ and Eu₂SiO₄ compared to those annealed in O₂ ambient. The spectral results revealed that a broad luminescence associated with Eu²⁺ ions, with a maximum intensity at 600 nm and a FWHM of 110 nm, was observed from the thin film annealed at 1000 °C in N₂ ambient. However, a series of narrow PL spectra from Eu³⁺ ions were observed from the film annealed in O₂ ambient.     

Microstructure and luminescent properties of Eu2W2O9 phosphors

A homogeneous Eu₂W₂O₉ phase with small grains (～4.0μm) was formed for the specimens fired below 1175°C. As the firing temperature was increased above 1150°C, grain growth occurred and the grain shape changed from faceted to round. The excitation spectra of the Eu₂W₂O₉ phosphor were similar to those of the Eu₂(WO₄)₃ phosphor, but the absorption band due to the O^2?→W⁶⁺ ligand to metal charge transfer was shifted to lower energies and the ⁷F_o→⁵H₃ and ⁷F_o→⁵F_2,4 transitions were not found. The intensity of the excitation and emission spectra of the Eu₂W₂O₉ phosphor considerably increased with increasing firing temperature, due to the increased grain size and changed grain shape. The intensity of the red emission band of the Eu₂W₂O₉ phosphor was higher than that of the Eu₂(WO₄)₃ phosphor. Moreover, the addition of LiCl to the Eu₂W₂O₉ phosphors considerably enhanced the intensity of their emission spectra, probably due to the increased grain size. Therefore, LiCl-added, Eu₂W₂O₉ phosphor is a promising candidate material for red color emission.     

Structural and Optical Properties of Size and Morphology Controllable Nanoscale SrAl2O4: Eu2+, Dy3+

Abstract

Nanoscale SrAl₂O₄: Eu²⁺, Dy³⁺ with controllable size and morphology was synthesized by sol-gel auto-combustion method. The surface morphology and structural characterization were carried out with TEM and XRD. Optical properties were analyzed by comparing excitation spectra, emission spectra and afterglow decay of the nanoscale phosphor with that of the bulk phosphor. The results showed that citric acid acted as a soft template in the reaction system. The morphology and size changed clearly with pH value and sintering temperature. The crystallinity was affected by the quantity of citric acid. Both the nanoscale phosphors with different particle size and the bulk one have the strongest emission at 525?nm. But their strongest peaks in excitation spectra are very different from each other. The phosphorescence of nanoscale phosphor decays more rapidly than that of the bulk phosphor.     

An Abnormal Photoluminescence Enhancement in (Eu,Yb) Co-doped SiO2 Thin Film

We report on the photoluminescence (PL) properties of europium (Eu) and ytterbium (Yb) co-doped SiO₂ thin film. The Eu (both Eu²⁺ and Eu³⁺) PL and the Yb³⁺ PL is co-related under different temperature annealing. However, upon 1100°C anneal, the Eu PL intensity is significantly stronger than other temperatures anneal. Transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction results, suggest that meta-stable Eu²⁺-related silicates (EuSiO₃) have formed in the oxide as well as the formation of Yb₂Si₂O₇.     

Effects of Al<Superscript>3+</Superscript> substitution on the luminescence properties of LuNbO<Subscript>4</Subscript> doped with Eu<Superscript>3+</Superscript> and Tb<Superscript>3+</Superscript> ions

The effect of Al³⁺ substitution on the enhancement of the luminescence of Lu_1–xAl_xNbO₄:Eu³⁺ and Lu_1–xAl_xNbO₄:Tb³⁺ was investigated. X-ray diffraction patterns confirmed that the Eu³⁺, Tb³⁺, and Al³⁺ ions were fully incorporated into the Lu³⁺ sites. In the case of Lu_1–xAl_xNbO₄:Eu³⁺, the predominant red emission (614 nm) was assigned to the ⁵D₀?→?⁷F₂ transition of Eu³⁺ and for x?=?0–0.05, its intensity increased up to ~125 and 108% under 395 nm (⁷F₀ → ⁵L₆) and a charge transfer band excitation, respectively. For Lu_1–xAl_xNbO₄:Tb³⁺, the strongest emission band peaking at 551 nm was attained in the green region among multiple emission bands corresponding to the ⁵D₄?→?⁷F_J transitions of Tb³⁺. Increasing the x values from 0 to 0.05 increased the green emission significantly by ~137%. These phenomena were explained by the local structural distortions and crystal field asymmetry surrounding Eu³⁺ and Tb³⁺, which were attributed to a large difference in the ionic radii of Al³⁺ and Lu³⁺.     

Microwave power detection using ferroelectric thin film varactors

ABSTRACT

LaAlO₃ powders are prepared by coprecipitation of La(OH)₃ and Al(OH)₃, followed by solid state reaction method or molten salt synthesis method. The crysatlline phase evolution, micro morphology and luminescence properties of the calcined products are systematically studied by XRD, SEM/EDX and fluorescence spectroscopy. The results show that LaAlO₃ powders with high purity could be obtained at 1000°C/3h with the help of melton salt Na₂SO₄, however, impurities exist in the solid state reaction products under the same calcination condition. The as prepared sub-micrometer LaAlO₃ powders doped with Eu³⁺ ion by the molten salt method show two dominant emmision peaks of 596nm and 618nm under excitation of near ultraviolet light (314nm), both emmision peak intensity reach maximum at the Eu³⁺ doping concentration of x = 0.08. At higher Eu³⁺ doping concentration, the emmision peak intensity decreases due to the concentration quenching.     

Mechanoluminescence of Ca2MgSi2O7: Eu2+, Dy3+ Phosphor by Impulsive Deformation

Di-calcium magnesium silicate phosphor doped with Eu²⁺ and Dy³⁺ was prepared using solid state reaction technique under a reducing atmosphere. Prepared sample suffered an impulsive deformation with an impact of a piston for mechanoluminescence (ML) investigations. A temporal characteristic of ML of the phosphor was observed, which expressed single sharp peak with a long decaying section. In order to investigate about the luminescence centre responsible for ML peak, ML spectrum of the same phosphor was also observed. ML spectrum recorded shown similarity in shape as well as peak wavelength with Photoluminescence (PL) spectrum that verifies the existence of single emission centre due to the transition of Eu²⁺ ions i.e. transitions from any of the sublevels of 4f⁶5d¹ configuration to ⁸S_7/2 level of the 4f⁷ configuration. Decay rates for different impact velocities were also calculated using curve fitting technique. Time of ML peak and rate of decay did not change largely with respect to increasing impact velocity of the load and peak ML intensity varied linearly. Increasing impact velocity causes more number of Eu²⁺ ions to get excited to the higher energy level, subsequently de-excitation of more Eu²⁺ ions occurs. This gives rise to increase in ML intensity.     

Defects in BaMgAl10O17: Eu2+ Blue Phosphor

The luminescent properties of BaMgAl₁₀O₁₇: Eu²⁺ blue phosphor are closely related to the valence state of europium inside the crystal and its defect structure. Because of the complexity of the BAM structure, research was carried out to study the europium-related defects by computer simulation. Two different Mg distributions were found to have the same lattice energy, but the arrangement of Mg affected the defect energy and Eu position. Eu³⁺ behavior was also discussed to address the oxidation-induced luminescent degradation. Two energetically most-favorable positions were found for europium, depending on the oxidation state: the Beevers-Ross site on the conduction plane for Eu²⁺, and the Al(2) site in the middle of the spinel block for Eu³⁺. Results of defect complex and bond-valence calculations suggested that the large europium ion can reside in the oxygen close-packed spinel blocks. A comparison of europium defect properties calculated with two different potential models suggests that results of the simulations are potential independent.     

The preparation of ZnGa2O4 doped with Mn‐Mg and Tm for green and blue phosphors

Phosphor powders of zinc gallate (ZnGa₂O₄) with Mg and Mn for green and Tm‐Mg for blue luminescence were prepared by solid state reaction method for their improved luminescent properties. Green‐luminescence emitting ZnMnGa₂O₄ reached maximum intensity at Mn = 0.005 mol% and further improvement was achieved by the addition of Mg²⁺. Tm‐Mg based zinc gallate phosphor exhibited a strong blue emission, centered at ∼420 nm with the maximum intensity achieved for 0.003 mol% of Mg and 0.015 mol% of Tm. This study established the possibilities of controlling the luminescent characteristics of zinc gallate by adding various elements. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Optical characteristics of Bi4-xEuxTi3O12 ferroelectric thin films on fused silica substrates

Bi_4-xEu_xTi₃O₁₂ (BEuT) ferroelectric thin films were prepared on fused silica substrates by using chemical solution deposition technique. The attained samples had a polycrystalline bismuth-layered perovskite structure, and their optical properties were composition dependent. The thin film samples had good optical transmittance above 500?nm wavelength. A blue shift of the optical absorption edge was observed in the BEuT thin films with increasing Eu³⁺ concentration. The optical band gaps of BEuT thin films were estimated to be about 3.57, 3.60, 3.61, 3.63, and 3.69?eV for the samples with x?=?0.25, 0.40, 0.55, 0.70, and 0.85, respectively. Photoluminescence measurements showed that two emission peaks of BEuT thin films originated from two transitions of ⁵ D ₀????⁷? F ₁ (594?nm) and ⁵ D ₀????⁷? F ₂ (617?nm) had maximum intensities when Eu³⁺ concentration was x?=?0.40. The relatively high quenching concentration of Eu³⁺ content was thought to be related to the layered structure of BEuT thin films. These results suggested that multifunctional BEuT thin film materials could have promising applications in optoelectronic devices.