Luminescence and recombination processes in bulky Li6Gd x Y1 − x (BO3)3:Eu crystals

The luminescence and recombination processes in crystals of lithium borates Li₆Gd _x Y_{1 − x} (BO₃)₃:Eu have been investigated. The steady-state X-ray luminescence (XRL) spectra, the temperature dependences of the XRL intensity, and the thermally stimulated luminescence (TSL) spectra have been measured for the Li₆Gd(BO₃)₃, Li₆Eu(BO₃)₃, Li₆Y_0.5Gd_0.5(BO₃)₃:Eu, and Li₆Gd(BO₃)₃:Eu compounds in the temperature range of 90–500 K. It is established that the band at 312 nm, which is due to the ⁶ P _J → ⁸ S _7/2 transitions in Gd³⁺ ions and the group of lines at 580–700 nm, which are due to the ⁵ D ₀ → ⁷ F _J (J = 0 … 4) transitions in Eu³⁺ ions dominate in the XRL spectra. The XRL intensity in these bands increases several times with a change in temperature from 100 to 400 K for undoped crystals. The likely mechanisms of the observed temperature dependence of the XRL intensity and their relationship with the features of electronic-excitation energy transfer in these crystals are discussed. The spectra of all crystals under study exhibit a dominant composite TSL peak with a maximum at 110–160 K and a series of weaker peaks, the composition and structure of which depend on the crystal type. The nature of the shallow traps, which are responsible for the TSL at temperatures below room, and their relationship with the defects of lithium cation sublattice are discussed.     

Ultraviolet luminescence of Li6Gd(BO3)3: Ce crystals under selective excitation in the region of 4d → 4f transitions

The subnanosecond time-resolved ultraviolet luminescence of Li₆Gd(BO₃)₃: Ce crystals under selective excitation by ultrasoft X-rays in the region of the 4d??4f core transitions at temperatures of 7 and 293 K has been investigated for the first time. The performed investigation has revealed the following features: an intense fast component of the luminescence decay kinetics in the subnanosecond range due to the high local density of electronic excitations and the processes of Auger relaxation of the core hole; the modulation of the luminescence excitation spectrum by the ??giant resonance?? absorption band of the 4d-4f photoionization in the energy range 135?C160 eV; and a new broad luminescence band at an energy of 4.44 eV due to the direct radiative recombination between the genetically related electron in the states of the conduction band bottom and hole in the 4f ground state of the Ce³⁺ ion.     

微波热效应合成(Y,Gd)BO3:Eu3+荧光体

本文首次报道用微波热效应法合成(Y,Gd)BO3:EU3+荧光体粉晶材料,X射线粉末衍射确认为六方晶系,晶胞参数a=0.3796nm,c=0.8835nm;在589nm和613.0nm监测下,其激发光谱峰是239.0nm和240.0nm,半高宽40nm.在240.0nm激发下,589nm和612-626nm的荧光强度比为1.9/1.     

Temperature dependence of the luminescence properties of LaCl3：Ce crystal

The optical properties of LaCl3：Ce crystal are reported in this paper. Optical transmission spectrum, photoluminescence and time resolved photoluminescence spectra at different temperatures are investigated. It is found that optical transmittance is as high as 80% between 320 nm and 600 nm, and no obvious absorption band is found in this region. Emission intensity and decay time of photoluminescence are quite stable with the change of the temperature between 80 K and 500 K. No thermal quenching is present up to 500 K, and decay time keeps at 17±2 ns. With the increase of the temperature, the whole emission bands and excitation bands present broadening and overlapping, leading to the strengthening of re-absorption of the Ce^3＋ emission, which makes the emission spectra have a red shift trend.     

均一球形PDP用荧光粉(Y,Gd)BO3:Eu的合成

利用共沉淀法通过控制稀土离子浓度、沉淀温度等得到稀土氧化物前驱体沉淀,再将其和H3BO3按化学计量比混合煅烧制备出了平均粒径在0．5～1．0μm的球形、粒径分布较小和无团聚的(Y,Gd)BO3：Eu荧光粉,其性能在一些方面优于商用荧光粉。利用X射线衍射、SEN、粒度分析仪和PL光谱进行表征。研究了不同的煅烧温度对荧光粉性能的影响,结果发现用本实验方法在800℃煅烧即可得到纯相的(Y,Gd)BO3：Eu。而传统固相合成纯相的(Y,Gd)BO3：Eu反应温度高达1200℃。因本方法工艺较易控制,适于在工业生产上推广。     

Luminescence of the compounds Y0.5 − x Li1.5PO4:Eu x

In this paper for the first time, the compounds Y_{0.5 ? x} Li_1.5PO₄:Eu _x (YLP:Eu) were synthesized by the simple method of solid state reaction. The technology takes much time dry low temperature and little time calcined to synthesize rare earth phosphates. Their structures were analyzed by X-ray powder diffraction experiment. The excitation and emission spectra were measured at room temperature. Y_{0.5 ? x} Li_1.5PO₄:Eu _x shows the characteristice emissions of Eu³⁺ (⁵ D ₀-⁷ F _{1, 2, 3, 4} transitions dominated by ⁵ D ₀-⁷ F ₄). Incorporation of Li⁺ ions in the phosphors promote the crystallinity, reduce the amount of Y₂O₃, and lower the cost of production, moreover, transition dominated by ⁵ D ₀-⁷ F ₄ is important for a number of practical applications.     

Spectral luminescence properties of Ca1 ? x Sr x F2:Ce3+ (0 < x <1) crystals

The luminescence, reflection, and luminescence excitation spectra of two-component Ca_{1 ? x} Sr _x F₂:Ce³⁺ (0.05 mol %) (x = 0.14, 0.25, 0.4, 0.6, and 0.75) have been studied at room temperature and T = 8 K. It is shown that the luminescence bands (upon 130-eV photon excitation) in the range of 200 to 400 nm are attributed to singlet and triplet self-trapped exciton luminescence and to 5d-4f transitions in Ce³⁺.     

Concentration dependence of EPR spectra in mixed (BaF2)1 − x (CeF3) x crystals

Physics of the Solid State - In the EPR spectra of the (BaF2)1 − x (CeF3) x system, additional lines appear as the concentration x in the mixture increases from 10−3 to 10−2, some...     

溶胶-凝胶法制备小颗粒(Y,Gd)BO3:Eu及其表征

用溶胶—凝胶方法制备了平均粒径为1～2μm的小颗粒、高发射效率的(Y,Gd)BO3：Eu红色发射荧光体。用XRD、SEM、粒度分析和PL光谱对荧光体作了表征和研究。常规固相反应合成(Y,Gd)BO3：Eu需在1200℃以上才能形成均一的固溶体。而溶胶—凝胶法制取稀土正硼酸盐800℃灼烧已可形成均一的单相(Y,Gd)BO3：Eu,在1100℃可得到发光亮度最高的荧光体。它的亮度是常规固相反应于1200℃制得的荧光体的120％。采用溶胶—凝胶法制取(Y,Gd)BO3：Eu荧光体,可在相当宽的实验条件范围内得到小粒径、窄分布和高亮度的荧光体,且有良好的颗粒形貌。     

Temperature dependence of the intensity of phonon-free luminescence lines of Rb3UO2F5 crystals in the 4.2–40 K range

We have investigated the behavior of the intensity of phonon-free lines appearing in the luminescence spectra of Rb₃UO₂F₅ crystals in the 4.2–40 K range due to a pure electron transition and its vibrational recurrences with the frequency of fully symmetrical stretching vibrations of the uranyl ion. It is shown that the temperature dependence of the total integrated intensity of these phonon-free lines, I_Σ, can be described using a model of configuration coordinates of an impurity center with one local vibration. An empirical expression has been obtained for the dependence I_Σ = I_Σ(T) in the form of the product I_Σ(T) = I₀(T)S_Σ(T), where the first factor describes the temperature dependence of the integrated intensity of the pure electron transition line and the second can be approximated by an exponential function of the Stokes parameter. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 129–131, January–February, 2000.     

Spectroscopic properties and diode-pumped 1594 nm laser performance of Er:Yb:Li6Y(BO3)3 crystal

An Er³⁺/Yb³⁺-codoped Li₆Y(BO₃)₃ crystal was grown by the Czochralski method. The polarized absorption spectra and the fluorescence decay curve were recorded. The efficiency of energy transfer from Yb³⁺ to Er³⁺ ions was estimated. Quasi-continuous-wave output power of 325 mW at 1594 nm was realized under the absorbed pump power of 10.4 W in a hemispherical cavity. The absorbed pump threshold and slope efficiency of the laser are 6.0 W and 7.2%, respectively. PACS 42.55.Xi; 42.70.Hj     

Specific features of electronic and magnetic states of the Y3Co binary compound in the (Gd1 − x Y x )3Co solid solution system

The electronic and magnetic properties of Y₃Co single crystals have been studied using neutron diffraction and electrical measurements. It has been established that these properties of Y₃Co and (Gd_{1 ? x} Y _x )₃Co crystals differ substantially. The most probable models of modification of the physical properties of the binary compound have been discussed.     

The investigation of the laser properties of a new class of the mixed Y x Sc1 ? x VO4:Nd3+ crystals

The investigation of structural perfection and laser properties of a new class of mixed vanadates Y _x Sc_{1 ? x} VO₄:Nd³⁺ was carried out in this work. The research of the structural perfection of the crystals was carried out by applying the X-ray diffractometer. It was shown that the Y _x Sc_{1 ? x} VO₄:Nd³⁺ crystals have a good structural perfection. The lasing experiment shows that the maximal CW output power of 2 W was achieved upon 5.8 W pumping. The maximal slope efficiency of 41.5% was obtained along the [100] crystallographic direction for the ??-polarization.     

Optical study of single crystals grown by the Czochralski method from Yb3+-doped (Gd1−x Y x )2SiO5 solid solution

Yb³⁺-doped crystals were grown by the Czochralski method from (Gd_0.5Y_0.5)₂SiO₅ melt employing seeds cut out from single crystals of Yb:Gd₂SiO₅ and Yb:Y₂SiO₅. XRD analysis revealed that the structure of the solid solution crystals grown is consistent with the structure of the seed, namely C2/c for the Yb:Y₂SiO₅ seed and P2₁/c for the Yb:Gd₂SiO₅ seed. Optical absorption spectra, emission spectra and luminescence decay curves were recorded at 10 K and 300 K. Analysis of gathered spectroscopic data made it possible to evaluate radiative transition rates for the ²F_5/2 multiplet of Yb³⁺ in the two structures and to assess crystal field splitting of multiplets involved in radiative transitions. It has been concluded that transition intensities and relaxation dynamics of Yb³⁺ in the systems studied are similar but the intensity distribution of emission and absorption bands depends significantly on the system structure. This feature, combined with inhomogeneous broadening of spectral lines, may be advantageous for the tailoring of lasers employing ytterbium-doped crystals for specific applications.     

Electron paramagnetic resonance of Gd3+ ions in Ca1 − x − y Y x Gd y F2 + x + y crystals

Electron paramagnetic resonance of Ca_{1 ? x ? y} Y _x Gd _y F_{2 + x + y} single crystals has revealed spectra that are not typical of gadolinium-doped CaF₂ crystals. These spectra have a nearly tetragonal symmetry and are most probably caused by Gd³⁺ ions localized in yttrium clusters. Weak spectra of tetragonal Gd³⁺ centers, whose parameters are close to those of a cubic gadolinium center caused by an isolated Gd³⁺ ion, have been also detected. These centers are attributed to isolated Gd³⁺ ions localized near octahedral rare-earth clusters or their associations.     

Ferrimagnetic order in the mixed garnet (Y1− x Gd x )3Fe5O12

Ferrimagnetic order in the mixed rare-earth iron garnet (Y₁?_?? _x Gd _x )₃Fe₅O₁₂ system has been reinvestigated to cover the temperature range 5.0 to 700?K. The magnetization versus temperature exhibits a systematic variation with changing concentration x. The ferric-ion exchange coupling is strong enough to determine the Curie temperature ≈559?K for all the values x. The compensation temperature at which the magnetization crosses zero (shows the minimum) demonstrates the applicability of the three-sublattice model. The magnetic moment at 5.0?K indicates reasonable agreement with the relation n _B?=?|21x???5.0|μ_B for the (Y₁?_?? _x Gd _x )₃Fe₅O₁₂ system. The compensation temperature decreases with decreasing x from 1.0 and reaches zero near x?=?0.24. An enlargement of coercive force in the hysteresis loop for the low-field M-H curve is clearly seen in near the compensation temperature, indicating that a single domain is formed and the rotation of this single domain occurs without building up a multidomain structure.     

(Y,Gd)Al3(BO3)4:Tb的真空紫外光谱特性

(Y,Gd)Al3(BO3)4属于三角晶系,具有R32的空间群,掺入Ce3 ,Tb3 杂质后,其晶格结构没有变化。(Y,Gd)Al3(BO3)4:Tb随着Gd3 摩尔浓度增大,基质吸收带红移。Gd3 和Tb3 之间存在着很有效的能量传递。Gd3 摩尔浓度在一定范围内(0~0·75mol)增大时,样品在120~300nm光谱范围内的激发强度均是增强的;但是,Gd3 浓度过高造成Gd3 的发射增强,GdAl3(BO3)4:Tb在120~240nm光谱范围内激发强度很明显下降。(Y,Gd)Al3(BO3)4:Ce,Tb在真空紫外激发下,发现Tb3 的发光明显的被Ce3 猝灭。     

Actively Q-switched laser performance of Nd:Gd x Y1−x VO4: a class of mixed vanadate crystals

We report for the first time the actively Q-switched laser performance of a class of mixed Nd:Gd _x Y_1−x VO₄ crystals. In comparison with the ordered Nd:GdVO₄ and Nd:YVO₄, an enhancement in both pulse energy and peak power is demonstrated in the low pulse-repetition frequency (PRF) range of 5–20 kHz, confirming Nd:Gd_0.64 Y_0.36VO₄ as the most advantageous in this respect. Laser pulses of 8.3-ns duration are generated at PRF=10 kHz with pulse energy and peak power being respectively 171 μJ and 20.6 kW. While for high-PRF operation (>∼40 kHz), the ordered Nd:GdVO₄ and Nd:YVO₄ prove to be superior to the mixed crystals.     

Pulsed EPR spectroscopy of Gd3+ centers in Ca1−x R x F2+x (R=La, Y) mixed crystals

A study of Gd³⁺ centers in Ca_1?x R _x F_2+x (R=La, Y) crystals using pulsed EPR spectroscopy is presented. The echo-induced EPR (ESE-EPR) spectrum shows, besides the signal of slightly perturbed cubic Gd³⁺ centers, a broad signal at g≈2 due to Gd³⁺ centers at low symmetry sites. To describe the effects of R³⁺ ions on the EPR Gd³⁺, a model, including cubic and linear R³⁺?2F _i ^? centers, is developed. Its predictions are compared with the experimental results. The composition dependence of the EPR signal due to slightly perturbed cubic Gd³⁺ centers in mixed Ca_1?x R _x F_2+x crystals is explained taking into account the different clustering tendency in La and Y crystals. Moreover, the formation of mixed clusters involving R³⁺ and Gd³⁺ ions is proposed for both series of samples. A greater clustering trend is found in the Y crystals than in the La ones. Gd³⁺ ions are found to be a “non innocent” paramagnetic probe for structural studies in these mixed crystals.