Spectral properties of rare-earth ions in nanocrystalline YAG:Re (Re=Ce, Pr, Tb)

Bulk and nanoscale powders of YAG:Re (Re=Ce, Pr, Tb) were synthesized by solid-state and sol-gel method. The changes of spectra and energy level were studied. Compared with the bulk YAG:Re (Re=Ce, Pr, Tb) crystals, the lattice parameter of YAG:Re (Re=Ce, Pr, Tb) nanocrystals decreases. It is also found that the excitation peaks of 5d energy levels shift in nanocrystals. The physical reason for spectral and energy level changes is a comprehensive result from the shift of energy centroid of the 5d orbit, the Coulomb interaction between 4f and 5d electrons and the crystal field splitting of the 5d energy level.     

YAG：Ce发光材料合成的助熔剂研究

采用高温固相法合成YAG:Ce荧光粉时,传统的以硼酸为助熔剂的产物硬度很大,处理过程中容易破坏晶体形貌,影响发光性能.采用氟化物助熔剂(MgF₂、CaF₂、SrF₂、BaF₂、AlF₃)及它们与H₃BO₃混合助熔剂来制备YAG:Ce,研究了助熔剂种类及其浓度对制得的粉体发光性能的影响,比较了它们的晶体形貌与物相组成.结果表明,采用不同助熔剂合成的YAG:Ce的激发光谱及发射光谱基本相同,而BaF₂、AlF₃、SrF₂及它们与H₃BO₃的混合助熔剂系列,可在一定程度上降低产品硬度、提高产品发光亮度;其中H₃BO₃~SrF₂系列、H₃BO₃~BaF₂系列的晶化程度与粒度分布均有改善;H₃BO₃~BaF₂系列的物相组成比较纯,除Y₃Al₅O₁₂主相外基本无杂相.     

Ce:YAG晶体和透明陶瓷的光学和闪烁性能

采用温梯法生长了Ce:YAG晶体和真空烧结法制备了Ce:YAG透明陶瓷,并对晶体和透明陶瓷的光学和闪烁性能进行了对比研究.Ce:YAG晶体和陶瓷都具有位于230,340和460 nm波段的Ce³⁺离子的特征吸收带和540 nm附近的发射峰,但Ce:YAG晶体同时存在296和370 nm的色心吸收,其发射峰位于398 nm,而透明陶瓷中不存在.Ce:YAG晶体和陶瓷的X射线荧光中均存在520 nm附近的Ce³⁺离子发射,但晶体中还存在由反格位缺陷引起的300 nm 关键词： Ce:YAG 闪烁晶体 透明陶瓷     

Integrated chemical process for exothermic wave synthesis of high luminance YAG:Ce phosphors

In this paper, high-luminance yellow-emitting Y₃Al₅O₁₂:Ce³⁺ phosphor (YAG:Ce) microparticles were prepared in a solid flame using a 1.425Y₂O₃+2.5Al₂O₃+0.15CeO₂+k(KClO₃+urea)+mNH₄F precursor mixture (here k is the number of moles of the KClO₃+urea red-ox mixture, and m is the number of moles of NH₄F). The self-sustaining combustion process for the entire reaction sample was provided by the heat generated from the KClO₃+urea mixture. Parametric studies demonstrated that the maximum temperature in the combustion wave varied from 885 to 1200 °C for k=2.0-3.0 mole and m=0-1.5 mole. X-ray analysis results showed that the product obtained in the solid flame consisted of Y₃Al₅O₁₂:Ce³⁺ and KCl phases. Therefore, after dissolving potassium chloride in distillated water, pure-phase YAG:Ce phosphor powder was obtained. The as-prepared YAG:Ce phosphor particles had diameters of 10-25 μm and good dispersity and exhibited luminescence properties comparable to those of YAG:Ce phosphor powders prepared by conventional high-temperature processing.     

YAG:Ce and YAP:Ce – Suitable Fast Detectors for Transmission Mössbauer Spectroscopy

Yttrium aluminum garnet and perovskite activated by cerium are fast mechanically and chemically resistant scintillation materials. Their mechanical properties enable easy and precise machining. Both scintillation materials have a decay time shorter than 100 ns and, therefore, are suitable to use for high counting rates. The luminescence maximum of YAP:Ce and YAG:Ce are 360 and 550 nm, respectively. Their luminescence bands correspond with the sensitivity spectral range of the most widely used photomultipliers. Moreover, the semiconductor light detectors can be used with YAG:Ce scintillation crystals. Theoretical and experimental comparative analysis of characteristics for both YAP:Ce and YAG:Ce detectors and good experience over relatively long periods of using these detectors allow us to draw a conclusion regarding their unconditional advantages over other commonly used detectors for transmission Mössbauer spectroscopy. The considerable improvement in data production enhances the capabilities of Mössbauer spectroscopy as a research and analytical tool.     

Effects of annealing temperature on YAG:Ce synthesized by spray-drying method

In this report, YAG:Ce phosphors were synthesized by spray-drying method. The effects of annealing temperature on crystal structure, morphology and photoluminescence property (PL) of as-prepared samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and spectrofluorometer, respectively. The XRD patterns showed all the samples are in consistence with a single garnet phase, and the location of strongest peak shifts to smaller angle with increasing the annealing temperature. The SEM micrographs revealed the sample annealed at 1200 °C appears to be a spherical polycrystalline aggregate; as the samples were annealed at 1300?1400 °C, spherical grains obviously grow up; but the sample annealed at over 1400 °C forms an irregular bulk. The emission spectra of samples indicated the PL of samples annealed at 1200?1400 °C improve with increasing the annealing temperature because of the diffusion of Si⁴⁺ ions; whereas the PL of sample annealed at the temperature over 1400 °C decreases likely resulting from inflection effects of multiangular shape of grains. Therefore, the samples annealed at 1400 °C are suitable for gaining phosphor with high brightness and good morphology.     

Yb:YAG及Cr,Yb:YAG晶体的发光特性

研究了室温下YbYAG的上转换荧光光谱,此荧光归因于Yb3+离子的"合作"发光和Yb3+离子到稀土杂质离子的能量转移.测试了YbYAG晶体的X射线荧光,发光峰对应于电荷迁移态到Yb3+离子的基态、激光态间的跃迁.研究了Cr,YbYAG晶体的荧光光谱,讨论了Cr4+激光输出的可能性.     

YAG:Ce3+的合成与光谱性能研究

采用共沉淀法合成了YAGCe3+(Y3Al5O12Ce3+)光致发光荧光粉并测定了其激发光谱、发射光谱及粒度对发光强度的影响.结果表明,YAGCe3+荧光粉激发光谱为双峰结构,两主峰分别位于近紫外和可见光区,发射光谱为宽峰,峰值为550nm.X射线衍射(XRD)分析表明该发光粉为纯YAG晶相.     

双掺Nd:Ce:YAG晶体激光输出特性

 为提高固体激光器的能量利用率,增大输出能量,将双掺Nd:Ce:YAG晶体的输出特性与普通Nd:YAG晶体进行了对比研究。分析了Nd³⁺和Ce³⁺的吸收光谱对激光晶体初始阈值反转粒子数的影响,结果显示:双掺Nd:Ce:YAG晶体可以提高晶体对泵浦光能量的利用率及激光器的输出能量,且可降低阈值泵浦能量。并分别检测了Nd:Ce:YAG激光晶体与Nd:YAG晶体的输出激光能量和阈值泵浦能量,实验结果表明：在输入电压为750 V时,Nd:Ce:YAG晶体与Nd:YAG晶体的输出能量分别为651.5 mJ 和390.4 mJ,能量利用率分别为2.31%和1.38%,激光振荡需要的泵浦能量阈值分别为10.56 mJ和15.21 mJ,且普通Nd:YAG晶体的斜效率为0.36%,而双掺Nd:Ce:YAG晶体的为0.49% 。     

电荷补偿剂对YAG:Ce荧光粉效率的影响

在研制传统的YAG:Ce3 荧光粉过程中引入NH4F作为助熔剂,BaF2和MgF2作为电荷补偿剂,使得荧光粉的性能得到有效的改善。助熔剂的引入使YAG:Ce3 荧光粉的合成温度由原来的1600℃降低到1340℃左右,这对于降低生产成本有着十分重要的意义。引入BaF2和MgF2作为电荷补偿剂,荧光粉的发光强度得到有效的提高。尤其是引入MgF2后,光致发光强度提高了42%。从XRD谱可以看出,Mg和Ba进入晶格取代了Y。通过对晶格常数的计算,发现Mg的引入可以部分补偿Ce3 掺杂带来的晶格增大。同时电荷补偿剂的引入使荧光粉达到电荷平衡:2AYYx→2Mg′Y→VO¨、2YYx→2Ba′Y V¨O减少了烧制过程中产生的氧空位缺陷的影响,从而减少了由于氧空位带来的无辐射跃迁。另外,以杂质离子的半径和原子的电负性为出发点,对发射光谱的峰位相对移动作了定性的解释。     

基于Ce:YAG单晶的白光发光二极管性能研究

以Ce:YAG单晶取代传统Ce:YAG荧光粉用于制备白光发光二极管(LED),研究了Ce:YAG单晶厚度及驱动电压的变化对其发射光谱、色坐标、亮度、光视效能和色温的影响。研究结果表明,在基于Ce:YAG单晶的白光LED中,发射光的色坐标以及蓝光与黄绿光之间的相对强度可通过对Ce:YAG单晶片厚度的改变进行调整。在恒定电压驱动下,白光LED样品的亮度、光视效能和色温均随单晶片厚度的减小而增加。当Ce:YAG单晶厚度为0.6mm时,可获得较纯的白发射光,并且其色坐标具有较高的可靠性和稳定性,基本不受驱动电压变化的影响。研究结果表明Ce:YAG单晶是一种可用于新型白光LED的理想荧光材料。     

Energy transfer in Y3Al5O12:Ce, Pr and CaMoO4:Sm, Eu phosphors

Non-radiative energy transfers (ET) from Ce³⁺ to Pr³⁺ in Y₃Al₅O₁₂:Ce³⁺, Pr³⁺ and from Sm³⁺ to Eu³⁺ in CaMoO₄:Sm³⁺, Eu³⁺ are studied based on photoluminescence spectroscopy and fluorescence decay patterns. The result indicates an electric dipole-dipole interaction that governs ET in the LED phosphors. For Ce³⁺ concentration of 0.01 in YAG:Ce³⁺, Pr³⁺, the rate constant and critical distance are evaluated to be 4.5×10⁻³⁶ cm⁶ s⁻¹ and 0.81 nm, respectively. An increase in the red emission line of Pr³⁺ relative to the yellow emission band of Ce³⁺, on increasing Ce³⁺ concentration is observed. This behavior is attributed to the increase of spectral overlap integrals between Ce³⁺ emission and Pr³⁺ excitation due to the fact that the yellow band shifts to the red spectral side with increasing Ce³⁺ concentration. In CaMoO₄:Sm³⁺, Eu³⁺, Sm³⁺-Eu³⁺ transfer occurs from ⁴G_5/2 of Sm³⁺ to ⁵D₀ of Eu³⁺. The rate constant of 8.5×10⁻⁴⁰ cm⁶ s⁻¹ and the critical transfer distance of 0.89 nm are evaluated.     

Cr,Tm:YAG晶体中的能量转移

通过对Cr:YAG、Tm:YAG和Cr,Tm:YAG晶体吸收光谱和发射光谱的比较,研究了Cr,Tm:YAG晶体中的能量转移过程.指出Cr3+→Tm3+能量转移过程中,无辐射能量转移占绝对优势.     

Luminescent and scintillation properties of YAG:Dy and YAG:Dy,Ce single crystalline films

The paper is devoted to investigation of the luminescent properties of Dy³⁺ and Dy³⁺-Ce³⁺ doped single crystalline films (SCF) grown by LPE method from PbO–B₂O₃ flux. We have found that the YAG:Dy and YAG:Dy,Ce SCFs possess bright cathodoluminescence in the visible range and good scintillation figure of merit. For this reason LPE grown YAG:Dy and YAG:Dy,Ce SCF are proposed for different applications, namely, as cathodoluminescence screens or screens for microimaging. The Dy³⁺ co-doping can be also proposed for improvement of the scintillation efficiency of the Ce³⁺ doped garnet compounds in the SCF form due to Dy³⁺→ Ce³⁺ energy transfer and removing the trap related centers in the above RT range.     

Cr，Tm∶YAG晶体中的能量转移

通过对Ｃｒ∶ＹＡＧ、Ｔｍ∶ＹＡＧ和Ｃｒ，Ｔｍ∶ＹＡＧ晶体吸收光谱和发射光谱的比较，研究了Ｃｒ，Ｔｍ∶ＹＡＧ晶体中的能量转移过程．指出Ｃｒ３＋→Ｔｍ３＋能量转移过程中，无辐射能量转移占绝对优势．     

Scintillating properties of LiYSiO_4:Ce

LiYSiO₄:Ce is a promising scintillator and some of its properties have been reported in previous papers. In this paper, samples doped with different concentrations of Ce are prepared and studied. First, the relative light yields of the samples are measured as 28.1%-37.1% compared with a standard anthracene crystal being irradiated by α particles and as ～ 27.2% compared with NaI being irradiated by X-rays. Second, the effects of sample thicknesses on light yields are presented. Finally the timing behaviors of samples with different doped concentrations being irradiated with alpha particles and X-rays are discussed. The result shows that LiYSiO₄:Ce is a kind of fast scintillator ( ～ 30 ns) with a moderate light yield that can be used for neutron detection.     

白光LED用新型Ce,Pr掺杂的YAG单晶荧光材料的光谱性能研究

为了改善白光LED用荧光材料效率低、均匀性差、光衰大、寿命短及物化性能差等不足,本文采用单晶荧光材料取代荧光粉来制备白光LED,并对白光LED用新型YAG单晶荧光材料的制备和光谱性能进行了研究.采用提拉法生长了白光LED用Ce∶YAG及Pr,Ce∶YAG晶体,并通过吸收光谱,激发、发射光谱对晶体材料的光谱特性进行表征.研究表明,Ce∶YAG单晶荧光材料可以被发射波长460 nm左右的蓝光芯片有效激发,产生一个范围为480~650 nm宽峰发射.通过Pr3+,Ce3+离子共掺杂可以有效补偿Ce3+离子单掺杂YAG荧光材料发光中的红色发光成分.     

YAG : Ce3+发光粉的粒度与LED匹配性

研究了不同粒度的YAG : Ce³⁺发光粉对LED亮度的影响,结果显示:粒度越大,封装后LED亮度越高;造成这种结果的主要原因是发光粉颗粒的晶格完整性不同。计算了发光粉在硅胶中的沉降速度,数据说明粒度越大,沉降速度越快,也就越不利于点胶。综合以上两个方面的结果认为发光粉的颗粒不宜太粗或太细,而且分布应该尽可能的窄,10~20 μm是粒径的理想范围。     

Lu2SiO5∶Ce荧光粉的热释光特性研究

采用溶胶-凝胶(Sol-Gel)技术,分别在空气中和石墨提供的弱还原气氛下制备出Lu2SiO5∶Ce0.006荧光粉。通过分析样品的结构,光致激发、发射谱和热释光谱等特性,发现弱还原气氛下制备的样品不仅光致发光强度比空气中的强,而且热释光曲线中598K处的高温热释光峰也得到了抑制。进一步考察空气中制备的Lu2SiO5∶Ce0.006,Kx(x=0.01～0.08)荧光粉,结果表明就光致发光和热释光特性而言,K+共掺杂具有与还原气氛类似的作用。综合以上两方面分析结果,可认为598K处热释光峰是由与Ce4+相关的缺陷引起的,并对K+共掺杂LSO∶Ce发光增强的原因给出了合理解释。     

Cr,Tm,Ho∶YAG激光器的理论模拟

为了使CTH∶YAG激光器的设计得到更好的优化，从晶体光谱吸收特性、离子间能量转移过程及准三能级运转方式对CTH∶YAG激光器的工作特性进行了理论分析；依据速率方程理论建立了CTH∶YAG激光器运转的理论模型.模拟能量输出与试验结果较好的吻合，验证了此理论模型描述CTH∶YAG激光器运转规律的合理性.模拟结果表明：CTH∶YAG激光器的激光脉冲输出与泵浦有较长的时间延迟且伴随较强的驰豫振荡，冷却温度对激光输出产生较大的影响.