缺陷态对LED用荧光材料热稳定性的影响

稀土或过渡金属离子掺杂荧光材料因其环保、易于制备、高效率、低成本、长发光寿命、全光谱、高亮度等性能在多重防伪、光学信息存储、温度传感等众多领域具有广泛的应用,特别是在LED照明领域。然而,荧光材料热稳定性差是阻碍其快速发展的核心问题。近年来,关于在热扰动作用下,缺陷态对载流子的俘获及释放过程,作为抑制LED用荧光材料热猝灭效应的有效途径被广泛研究。本文主要概述了LED用荧光材料中缺陷态对其热稳定性影响的研究现状,以及缺陷态作为陷阱中心对载流子的俘获、释放及其抑制LED用荧光材料热猝灭效应的机理,并对当前研究中存在的问题进行了总结和展望。     

Photoluminescence characteristics and energy transfer between Bi~（3＋） and Eu~（3＋） in Na_2O–CaO–GeO_2–SiO_2 glass

We report the photoluminescence（PL） of Eu^3＋-doped glass with Bi^3＋as a sensitizer. The specific glass system with the strong enhancement of the red emission of Eu3＋is obtained by adding a small number of Bi3＋ions instead of increasing the Eu^3＋ concentration. The emission band of Bi3＋overlaps with the excitation band of Eu^3＋ and the lifetime decay curves,resulting in a very efficient energy transfer from Bi^3＋ to Eu^3＋. The probability of energy transfer is strongly dependent on Bi^3＋ concentration. In addition, the intensity of 4f–4f transition is much stronger than that of a charge-transfer（CT） band in the excitation spectrum, which indicates that the Na2O–Ca O–Ge O2-Si O2 glass is a suitable red-emitting phosphor with high stability as a candidate for light-emitting diodes（LEDs）.     

A novel strong green phosphor： K3Gd（PO4）2：Ce^3＋, Tb^3＋ for a UV-excited white light-emitting-diode

A series of K3Gd1-x-y（PO4）2：xCe^3＋, yTb^3＋ phosphors are synthesized by the solid-sate reaction method. X-ray diffraction and photoluminescence spectra are utilized to characterize the structures and luminescence properties of the as-synthesized phosphors. Co-doping of Ce^3＋ enhances the emission intensity of Tb^3＋ greatly through an efficient energy transfer process from Ce^3＋ to Tb^3＋. The energy transfer is confirmed by photoluminescence spectra and decay time curves analysis. The efficiency and mechanism of energy transfer are investigated carefully. Moreover, due to the non- concentration quenching property of K3Tb（PO4）2, the photoluminescence spectra of K3Tb1-x（PO4）2：xCe^3＋ are studied and the results show that when x = 0.11 the strongest Tb^3＋ green emission can be realized.     

Synthesis and Crystal Structure of Mesityl Acetic Acid 3-Mesityl-2-oxo- 1-oxaspiro [4,4] non-3-en-4-yl Ester

The title compound mesityl acetic acid 3-mesityl-2-oxo-1-oxaspiro[4,4]non-3-en-4-yl ester (5, C28H32O4, Mr = 432.56), as a spiromesifen derivative, has been synthesized by the conden- sation reaction of 2,4,6-trimethylphenylacetic chloride with 4-hydroxyl-3-mesityl-1-oxa-spiro[4,4]- non-3-en-2-one (4), and its crystal structure was determined by single-crystal X-ray diffraction. The crystal belongs to the triclinic system, space group P1 with a = 7.9261(7), b = 8.2802(8), c = 18.7604(18) , α = 91.576(3), β = 93.277(2), γ = 95.306(12)o, V = 1223.3(2) 3, Z = 2, Dc = 1.174 g/cm3, F(000) = 464, μ = 0.077 mm-1, S = 1.001, the final R = 0.0624 and wR = 0.1415 for 2809 observed reflections with I 2σ(I) and 290 variable parameters. The crystal analysis results show that the five-membered cyclopentyl ring displays an envelope conformation with C(25) atom at the flap position, 0.537(3)  out of the mean plane formed by the other four atoms. The dihedral angles between the two benzene and furan rings are 70.0(2) and 80.67(3)o, respectively.     

Synthesis and Crystal Structure of 3-（2,4-Dichlorophenyl）- 4-dydroxy-5-cyclohexanyl-△3-dihydrofuran-2-one

The title compound 3-（2,4-dichlorophenyl）-4-dydroxy-3-（2,4-dichlorophenyl）-4- dydroxy-5-cyclohexanyl-A3-dihydrofuran-2-one 5 has been synthesized by the cyclization of methyl O-（2,4-dichlorophenyl-acetyl）-1-hydroxycyclo-hexane-carboxylate 4, and its crystal structure was determined by single-crystal X-ray diffraction. The crystal belongs to the triclinic system, space group Pi with a = 6.8192（3）, b = 10.5053（5）, c = 10.5811（5）A,α = 71.681（10）, β = 78.905（12）, γ = 81.036（12）°, C15H14C1203, Mr = 313.18, V= 702.44（6）A3, Z = 2, De= 1.481 g/cm^3, F（000） = 324,μ = 0.465 mm^-1, S = 1.006, the final R = 0.0331 and wR = 0.1363 for 2505 observed reflections with I 〉 2σ（I） and 183 variable parameters. The crystal analysis shows that the cyclohexene unit of the title compound has a quasi-chair conformation, and a one-dimensional chain structure is formed via the intermolecular hydrogen bond O（1）-H（101）…O（2）.     

Effects of Li~+ on photoluminescence of Sr_3SiO_5:Sm~(3+) red phosphor

The structure and photoluminescence (PL) properties of Sr3SiO5 : Sm3+ and Li+-doped Sr3SiO5 : Sm3+ red-emitting phosphors were investigated. Samples were prepared by the high-temperature solid-state method. PL spectra show that the concentration quenching occurs when the Sm3+ concentration is beyond 1.3 mol% in Sr3SiO5 : Sm3+ phosphor without doping Li+ ions. The concentration-quenching mechanism can be explained by the electric dipole-dipole interaction of Sm3+ ions. The incorporation of Li+ ions into Sr3SiO5 : Sm3+ phosphors, as a charge compensator, improves the PL properties. The lithium ions also suppress the concentration quenching in Sm3+ with concentration increased from 1.3 mol% to 1.7 mol%.     

新型电子俘获型材料β-Sr2SiO4:Eu2+, La3+长余辉和光激励发光性能的研究

通过高温固相法在还原气体保护下制备出β-Sr₂SiO₄: Eu²⁺, La³⁺系列样品. 通过样品光谱显示, 光致发光、余辉及光激励发光中心均来自于Eu²⁺离子; 并且La³⁺ 的掺入有效增强光致发光、余辉及光激励发光强度. 热释光与余辉衰减测试证明, 与单掺Eu²⁺样品所具备的缺陷数量相比, 共掺La³⁺样品在浅陷阱区(T1区)较多的俘获中心数量是导致其余辉性能优化的主要因素; 其光激励发光强度的增强则归因于在深陷阱(T3区)的俘获中心数量增加. 共掺样品放置15h并在980nm红外激光激励后, 表现出光激励长余辉发光现象. 此现象的出现, 为电子俘获型材料的浅陷阱对深陷阱中的载流子再俘获过程的存在提供了直接证据. 因此, β-Sr₂ SiO₄: Eu²⁺, La³⁺ 材料可视为一种潜在的长余辉和光激励发光材料.     

Effects of Li＋ on photoluminescence of Sr3SiOs： Sm3＋ red phosphor

The structure and photoluminescence （PL） properties of Sr3 SiO5： Sm3＋ and Li＋-doped Sr3SiOs： Sm3＋ red-emitting phosphors were investigated. Samples were prepared by the high-temperature solid-state method. PL spectra show that the concentration quenching occurs when the Sm3＋ concentration is beyond 1.3 mol% in Sr3SiOs： Sm3＋ phosphor without doping Li＋ ions. The concentration-quenching mechanism can be explained by the electric dipole-dipole interaction of Sm3＋ ions. The incorporation of Li＋ ions into Sr3SiOs： Sm3＋ phosphors, as a charge compensator, improves the PL properties. The lithium ions also suppress the concentration quenching in Sm3＋ with concentration increased from 1.3 tool% to 1.7 tool%.     

Characterization and luminescence of Eu/Sm-coactivated CaYAl3O7 phosphor synthesized by using a combustion method

A novel red-emitting phosphor, CaYAl3O7 : Eu 3+ , Sm3+ , is synthesized by a combustion method at a low temperature (850℃), and the single phase of CaYAl3O7 is confirmed by powder X-ray diffraction measurements. The photoluminescence property results reveal that the red emission intensity of Eu3+ is strongly dependent on the Sm3+ concentration. Only the Eu 3+ luminescence is detected in the Eu 3+ -Sm3+ co-doped CaYAl3O7 phosphor with 393 nm excitation. However, under the characteristic excitation (402 nm) of Sm3+ , not only the Sm3+ emission but also the Eu 3+ emission are observed. A possible mechanism of the energy transfer between Sm3+ and Eu 3+ is investigated in detail.     

Green long-after-glow luminescence of Tb~(3+)in Sr_2SiO_4

The green long-after-glow luminescence from Tb3＋-doped Sr2SiO4 phosphors, which are synthesized by the high temperature solid state reaction in a reductive atmosphere, is observed in this paper. The results show that under ultraviolet excitation, the obtained phosphors produce an intense green-lighting-emission from the Tb3＋, and the green-lighting long- after-glow luminescence related to Tb3＋ can last half an hour after the irradiation source has been removed. Moreover, the effects of co-doping Li＋, Dy3＋, Er3＋, Gd3＋, and Yb3＋ with Tb3＋ on the decay properties and thermoluminescence properties are investigated to confirm the long-after-glow mechanism.