Tm:Y2SiO5晶体的生长和光谱性质研究

采用中频感应提拉法生长了高质量的Tm:Y₂SiO₅(Tm:YSO)晶体,测定了晶体的晶格常数和分凝系数.运用劳厄照相法确定了单斜晶系Tm:YSO晶体的三个偏振轴〈010〉,D₁和D₂,在室温下测量了三个偏振轴方向的吸收光谱、荧光光谱和荧光寿命,计算了晶体吸收峰的吸收线宽和吸收截面.研究发现,相对于其他两个偏振轴方向,D₁方向在790nm处出现较强的吸收峰, 关键词： 2SiO₅')" href="#">Tm:Y₂SiO₅ 单斜晶系 吸收光谱 荧光光谱     

Degradation of Y2SiO5:Ce phosphor powders

The degradation of the cathodoluminescence (CL) intensity of cerium-doped yttrium silicate (Y₂SiO₅:Ce) phosphor powders was investigated for possible application in low voltage field emission displays (FEDs). Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of commercially available Y₂SiO₅:Ce phosphor powders. The degradation of the CL intensity for the powders is consistent with a well-known electron-stimulated surface chemical reaction (ESSCR) model. It was shown with XPS and CL that the electron stimulated reaction led to the formation of a luminescent silicon dioxide (SiO₂) layer on the surface of the Y₂SiO₅:Ce phosphor powder. XPS also indicated that the Ce concentration in the surface layer increased during the degradation process and the formation of CeO₂ and CeH₃ were also part of the degradation process. The CL intensity first decreased until about 300 C cm⁻² and then increased due to an extra peak arising at a wavelength of 650 nm.     

XPS analysis for degraded Y2SiO5:Ce phosphor thin films

X-ray photoelectron spectroscopy (XPS) results were obtained for standard Y₂SiO₅:Ce phosphor powders as well as undegraded and 144 h electron degraded Y₂SiO₅:Ce pulsed laser deposited (PLD) thin films. The two Ce 3d peaks positioned at 877.9 ± 0.3 and 882.0 ± 0.2 eV are correlated with the two different sites occupied by Ce in the Y₂SiO₅ matrix. Ce replaced the Y in the two different sites with coordination numbers of 9 and 7. The two Ce 3d XPS peaks obtained during the thin film analysis were also correlated with the luminescent mechanism of the broad band emission spectra of the Y₂SiO₅:Ce X₁ phase. These two different sites are responsible for the two main sets of cathodoluminescent (CL) and photoluminescence (PL) peaks situated at wavelengths of 418 and 496 nm. A 144 h electron degradation study on the Y₂SiO₅:Ce thin film yielded an increase in the CL intensity with a second broad emission peak emerging between 600 and 700 nm. XPS analysis showed the presence of SiO₂ on the surface that formed during prolonged electron bombardment. The electron stimulated surface chemical reaction (ESSCR) model is used to explain the formation of this luminescent SiO₂ layer.     

Y2O3:Yb3+,Tm3+纳米材料的可见及紫外上转换发光

通过燃烧法制备了Yb³⁺-Tm³⁺共掺的Y₂O₃纳米粉体,并对样品在980 nm激光照射下的上转换发光特性进行了研究.实验发现,样品在可见光区域能够产生强烈的蓝色发光(476 nm和487 nm)和较弱的红色发光(约650 nm),而且同时观察到了两个紫外发光峰¹I₆→³H₆ (~297 nm)和^{1关键词： 2O₃:Yb3+')" href="#">Y₂O₃:Yb3+ 3+}')" href="#">Tm³⁺ 上转换光谱 敏化 紫外发光     

Influence of calcining temperature on photoluminescence and thermal quenching in europium-doped Y2SiO5 using the MOD process

The crystalline Eu_0.25Y_1.75SiO₅ (EYSO) fine powders were prepared using metallorganic decomposition process, in which the pure X₁- and X₂-Y₂SiO₅ phases were obtained by calcining at temperatures from 850°C to 1600°C. The influence of calcining temperature on photoluminescence (PL) and thermal quenching were systematically investigated from room temperature to 573 K for the first time. As a consequence, the X₂-EYSO was higher in light emission intensities than the X₁-EYSO, but the X₁-EYSO possessed better temperature dependence of PL. The phase structure had a significant effect on the light emission intensity and energy as well as its temperature characteristics in the EYSO.     

激光吸收铒掺杂上转换材料的光谱特性实验分析

采用湿化学法制备了铒掺杂氧化钇上转换纳米粉体材料.研究了不同掺杂浓度、掺杂元素种类对材料显微结构、物相组成和光谱特性的影响.结果表明,通过控制掺杂元素的种类、掺杂浓度可以实现对光谱性能（包括光谱反射系数和上转换光谱）的调控.实验表明,该材料对106 μm激光具有较好的吸收性能. 关键词： 铒掺杂氧化钇纳米粉体 上转换材料 激光与红外复合隐身 光谱反射系数     

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.     

Energy transfer between activators at different crystallographic sites in Sr3SiO5:Eu

A yellow phosphor, Sr₃SiO₅:Eu²⁺, was synthesized by a high temperature solid-state method. Sr₃SiO₅:Eu²⁺ exhibits a single yellow emission under the blue radiation excitation. However, Sr₃SiO₅:Eu²⁺ shows a two-peak emission under the ultraviolet radiation excitation when Eu²⁺ doping content is less than 0.01 mol. Moreover, the blue emission disappears and the yellow emission reaches the peak value when Eu²⁺ doping content is 0.01 mol. Namely, the energy transfer takes place between the Eu²⁺ activators, which is located at two different crystallographic sites in the Sr₃SiO₅. And the energy transfer mechanism is the dipole-dipole interaction.     

Ultraviolet upconversion luminescence in Er-doped Y2O3 excited by 532 nm CW compact solid-state laser

Ultraviolet upconversion emissions at 262, 276, 308 and 320 nm were observed from Er³⁺-doped Y₂O₃ with a 532 nm continuous wave compact solid-state laser excitation. Power-dependence analysis demonstrates that two-photon upconversion process populates the ⁴D_5/2, ²H_9/2 and ²P_3/2 states. The energy transfer upconversion (ETU) plays an important role in populating ⁴D_5/2 and ²P_3/2 states. It appears that ²P_3/2 state population originates from ETU ²H_11/2+²H_11/2→⁴I_13/2+²P_3/2, moreover, a subsequent excited state absorption (ESA) from the ⁴I_9/2 level.     

Preparation and luminescent properties of cubic Eu:Y2O3 nanocrystals and comparison to bulk Eu:Y2O3

Y₂O₃:Eu³⁺ nanocrystals were prepared by combustion synthesis. The particle size estimated by X-ray powder diffraction (XRD) was about 10 nm. A blue-shift of the charge-transfer (CT) band in excitation spectra was observed in Y₂O₃:Eu³⁺ nanocrystals compared with bulk Y₂O₃:Eu³⁺. The electronic structure of Y₂O₃ is calculated by density functional method and exchange and correlation have been treated by the generalized gradient approximation (GGA) within the scheme due to Perdew-Burke-Ernzerhof (PBE). The calculated results show that the energy centroid of 5d orbital in nanocrystal has increasing trend compared with that in the bulk material. The bond length and bond covalency are calculated by chemical bond theory. The bond lengths of Y₂O₃:Eu³⁺ nanocrystal are shorter than those of the bulk counterpart and the bond covalency of Y₂O₃:Eu³⁺ nanocrystal also has an increasing trend. By combining centroid shift and crystal-field splitting, the blue-shift of the CT band is interpreted.     

Enhanced luminescence of Dy in Y3Al5O12 by Bi co-doping

In the present paper, phosphors with the composition Y_3−x−yAl₅O₁₂:Bi³⁺_x, Dy³⁺_y were synthesized with solid state reactions. The luminescence properties of Bi³⁺ and Dy³⁺ in Y₃Al₅O₁₂(YAG) and the energy transfer from Bi³⁺ to Dy³⁺ were investigated in detail. Bi³⁺ in YAG emits one broad band peaking at 304 nm which can be ascribed to the transition from excited states ³P_{0, 1} to ground state ¹S₀. Dy³⁺ in YAG emits two groups of peaks around 484 and 583 nm, respectively, which can be ascribed to the transitions from excited state ⁴F_9/2 to ground states ⁶H_15/2 and ⁶H_13/2. The co-doping of Bi³⁺ enhances the luminescent intensity of Dy³⁺ by ∼7 times because Bi³⁺ can transfer the absorbed energy to Dy³⁺ efficiently. The mechanism of energy transfer was also discussed.     

A 1.7-ps pulse mode-locked Yb3+:Sc2SiO5 laser with a reflective graphene oxide saturable absorber

By using a reflective graphene oxide as saturable absorber,a diode-pumped passively mode-locked Yb3+:Sc2Si O5(Yb:SSO)laser has been demonstrated for the first time.Without extra negative dispersion compensation,the minimum pulse duration of 1.7 ps with a repetition rate of 94 MHz was obtained at the central wavelength of 1062.6 nm.The average output power amounts to 355 m W under the absorbed pump power of 15 W.The maximum peak power of the mode-locking laser is up to 2.2 k W,and the single pulse energy is 3.8nJ.     

Yb3+:Gd2SiO5晶体的结构和光谱性能

采用提拉法成功生长尺寸为φ30 mm× 75 mm的15at.%Yb³⁺:Gd₂SiO₅单晶, 并用Reitveld全谱拟合方法确定了其晶格常数、原子坐标和温度因子等参数. 用吸收光谱计算了Yb³⁺离子²F_7/2↔ ²F_5/2能级跃迁的振子强度、谱线强度、跃迁概率、 能级寿命和积分发射截面等光谱参数, 并根据激光性能评估得出结论: 表明该晶体具有较大的阈值特性, 有望采用大功率激光二极管泵浦实现可调谐或超快激光输出.     

Spherical Zn2SiO4:Eu@SiO2 phosphor particles in core-shell structure: Synthesis and characterization

Spherical SiO₂ particles have been coated with Zn₂SiO₄:Eu³⁺ phosphor layers by a Pechini sol-gel process. The microstructure and luminescent properties of the obtained Zn₂SiO₄:Eu³⁺@SiO₂ particles were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and lifetime. The results demonstrate that the Zn₂SiO₄:Eu³⁺@SiO₂ particles, which have regular and uniform spherical morphology, emitted an intensive red light emission at 613 nm under excitation at 395 nm. Besides, the effects of the Eu³⁺ concentration, annealing temperature and charge compensators of Li⁺ ions on the PL emission intensities were investigated in detail.     

Enhanced photoluminescence properties of Zn2SiO4:Mn co-activated with Y/Li under VUV excitation

A series of green phosphors Zn_1.92−2xY_xLi_xSiO₄:0.08Mn²⁺ (0≤x≤0.03) were prepared by solid-state synthesis method. Phase and lattice parameters of the synthesized phosphors were characterized by powder X-ray diffractometer (XRD) and the co-doped effects of Y³⁺/Li⁺ upon emission intensity and decay time were investigated under 147 nm excitation. The results indicate that the co-doping of Y³⁺/Li⁺ has favorable influence on the photoluminescence properties of Zn₂SiO₄:Mn²⁺, and the optimal photoluminescence intensity of Zn_1.90Y_0.01Li_0.01SiO₄:0.08Mn²⁺ is 103% of that of commercial phosphor when the doping concentration of Y³⁺/Li⁺ is 0.01 mol. Additionally, the decay time of phosphor is much shortened and the decay time of Zn_1.90Y_0.01Li_0.01SiO₄:0.08Mn²⁺ is 3.39 ms, shorter by 1.83 ms than that of commercial product after Y³⁺/Li⁺ co-doping.     

Near infrared to red and yellow to blue upconversion emissions from Pr: ZrF4-BaF2-LaF3-YF3-AlF3-NaF glasses

This paper describes the development and a detailed analysis carried out on the luminescence characteristics of Pr³⁺ doped ZrF₄-BaF₂-LaF₃-YF₃-AlF₃-NaF glasses. In the present work our objectives are to elucidate the possible mechanisms that are responsible for NIR to red upconversion process and yellow to blue upconversion emission in terms of energy level schemes from the praseodymium containing fibre optical glass composition. We have studied their different physical and optical properties. Besides our investigation on the upconversion emission of these glasses, normal fluorescence studies have also been undertaken in explaining the mechanisms in demonstrating bright red and blue emissions upon excitations at visible and UV wavelengths. Besides these measurements works, a bright blue colour emission was observed under an UV source and upconverted prominent red emissions were observed with a laser diode (LD of ). Similarly under a yellow light source, a blue colour emission was observed from these praseodymium glasses studied.     

Crystal fields of Pr in LiYF4 under pressure

Fluorescence spectra of LiYF₄:Pr³⁺ have been measured between 12,000 and 22,000 cm⁻¹ under pressures up to 10 GPa. In total, 25 crystal field energy levels were obtained and used for the determination of free-ion and crystal field parameters under pressure. According to the nephelauxetic effect, the free-ion parameters decrease with increasing pressure. The relative decrease is larger for the Slater than for the spin-orbit coupling parameter. This behavior is consistent with former studies on Pr³⁺ in different crystals and can be explained by a special covalency model. According to an effective D_2d symmetry, five crystal field parameters B₀²(f,f), B₀⁴(f,f), B₄⁴(f,f), B₀⁶(f,f), and B₄⁶(f,f) are non-zero. The pressure-induced changes of these parameters have been determined up to the maximum pressure of 10 GPa. In order to improve the calculation of the crystal field levels, the configuration interactions with the 4f¹6p¹ configuration have been taken into account. The effect of these interactions are also analyzed under pressure and distinct improvements of the energy level calculations have been obtained.     

Preparation and upconversion properties of Ba2ErF7 and Ba2ErF7:Yb powders

Novel Ba₂ErF₇ and Yb³⁺-doped Ba₂ErF₇ powders were synthesized by a coprecipitation method. In Ba₂ErF₇ sample, abundant upconverted emission bands from violet to infrared region are observed under 980 nm excitation, whereas only green and red emissions are observed under 812 nm excitation. Under the two excitations, the luminescence decay curves of the green and red emissions are measured and the quenching behaviors of Yb³⁺ doping are also explored. It is found that a suitable Yb³⁺ concentration can efficiently enhance the intensity ratio of the blue and violet emissions to the green and red ones, which may be due to the competition between the energy transfer process from Er³⁺ to Yb³⁺ and the sensitizing process from Yb³⁺ to Er³⁺ in Ba₂ErF₇:Yb³⁺. This indicates that the Yb³⁺-doped Ba₂ErF₇ might be a good candidate for blue and violet upconversion phosphor.     

Oxide coatings on Y3Al5O12:Tb particles

A coating method with precipitating process was developed to reduce the particle size and to improve the particle dispersion of Y₃Al₅O₁₂:Tb³⁺ phosphor prepared by sol-gel method. The particle morphology was observed by using SEM and TEM; and the particle size and its dispersion was measured by using laser scattering technique. Several coating materials were tested. Among them, Al₂(SiO₃)₃ coating not only reduced the particle size from several micrometers to ∼1 μm and improved the particle dispersion, but also well kept luminescent intensities and improved the duration of the phosphor under the bombardment of cathode ray. The mechanism of the particle size reduction was proposed.     

Improved photoluminescence and afterglow in CaTiO3:Pr with addition of nanosized SiO2

Enhancement of the ¹D₂-³H₄ red emission in CaTiO₃:Pr³⁺ with addition of nanosized SiO₂ fabricated by a solid state reaction method is reported. The dynamical processes for the improvement of red emission were systematically investigated using photoluminescence (PL) and PL excitation spectra, and diffused reflectance spectra as well as time decay patterns of PL and persistent afterglow. Higher efficiency of energy transfer from CaTiO₃ host to the activator Pr³⁺ due to the improvement of crystallinity by SiO₂ addition was discussed in comparison with that of the SiO₂ free sample. The enhancement of persistent afterglow after the cessation of excitation in SiO₂ added CaTiO₃:Pr³⁺ was also analyzed by theoretically fitted results.