Timing characteristics of the scintillation response of Gd3Al2Ga3O12:Ce and Gd3Al2.6Ga2.4O12:Ce single crystal scintillators

The timing characteristics of scintillation response of Czochralski-grown Gd₃Al₂Ga₃O₁₂:Ce and Gd₃Al_2.6Ga_2.4O₁₂:Ce single crystals were compared. The photoelectron yield, scintillation decay times, and coincidence time resolution were measured. At 662 keV γ-rays, the photoelectron yield of 6200 phe MeV⁻¹ obtained for Gd₃Al₂Ga₃O₁₂:Ce is higher than that of 4970 phe MeV⁻¹ obtained for Gd₃Al_2.6Ga_2.4O₁₂:Ce, while an inferior energy resolution of the former (7.2% vs. 5.6%) is observed. Scintillation decays are approximated by sum of exponentials with the dominant fast component decay time and its relative intensity of 89 ns (73%) for Gd₃Al₂Ga₃O₁₂:Ce and 136 ns (69%) for Gd₃Al_2.6Ga_2.4O₁₂:Ce. The coincidence time resolution obtained for Gd₃Al₂Ga₃O₁₂:Ce is superior than that of Gd₃Al_2.6Ga_2.4O₁₂:Ce. The normalized time resolution was also discussed in terms of a number of photoelectrons and decay characteristics of the light pulse.     

掺Pb,Ga对Ce:YIG晶体磁光性能的影响

研究了掺Pb,Ga对Ce:YIG晶体的晶场、交换作用和磁光Faraday效应的影响.当Ga³⁺离子取代量为12%时，交换作用有效场减少51%，导致Ce³⁺离子最低两个能级的占有概率之差减少49%.Ga³⁺离子取代，同时影响分子场和晶场；而Pb²⁺离子的取代，只影响晶体场，对分子场的影响甚微.掺杂对稀土石榴石晶体的磁光性能有较大影响. 关键词： PbGaCe:YIG晶体 晶场 超交换作用 磁光效应     

Metamagnetism in Ce(Ga,Al)2

Effect of Al substitution on the magnetic properties of Ce(Ga_1−x Al _x )₂ (x=0, 0.1 and 0.5) system has been studied. The magnetic state of CeGa₂ is found to be FM with a T _C of 8 K, whereas the compounds with x=0.1 and 0.5 are AFM and possess T _N of about 9 K. These two compounds undergo metamagnetic transition and the critical fields are about 1.2 T and 0.5 T. respectively at 2 K. These variations are explained on the basis of helical spin structure in these compounds.     

Improvement of the scintillation properties of Gd3Ga3Al2O12:Ce,B single crystals having tailored defect structure

A novel approach is reported to minimize various defect centers in Ce doped Gd₃Ga₃Al₂O₁₂ single crystals to improve the scintillation properties. The crystals of Gd₃Ga₃Al₂O₁₂ codoped with 0.2 at% Ce and B (GGAG:Ce,B) have been grown in air and argon ambient using the Czochralski technique. The scintillation light output of crystals grown in Ar ambient was significantly increased after annealing the crystals in air. The measured light output of 60000 ph/MeV for annealed crystals is the highest value reported among this class of materials. As a consequence, the energy resolution at 662 keV gamma‐rays from a ¹³⁷Cs source was improved from 8% for the crystals grown in air to 6% for crystals grown in Ar and subsequently annealed in air. Further, the thermal quenching energy of photoluminescence (PL) emission was increased to be 470 meV for the annealed crystals. The thermoluminescence (TL) measurements suggest that the crystals grown in Ar ambient and post‐growth annealed in air may have a lesser concentration of trap centers which subsequently lead to the improvement in optical and scintillation properties leading to a superior detector performance. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Ce、Ga、La掺杂二维SnO2电子结构及光电性质的第一性原理研究

二维材料具有优异的光学、力学、热学、磁学等性质,成为研究的热点之一. SnO₂薄膜中的电子迁移率非常高,兼具透明和良好的导电性能,是一种性能绝佳的半导体材料.本文用密度泛函理论框架下的第一性原理研究了二维SnO₂及其掺杂体系的电子结构、电子态密度、导电性能及光学性质,计算结果表明：相比较于三维SnO₂,二维SnO₂的费米能级附近产生很多杂质能级,提高了载流子浓度,带隙明显变窄,电子的局域性增强,导带中电子的有效质量增加了,电子跃迁更容易发生,增加了材料的导电性能;二维SnO₂比三维SnO₂材料的电极化能力强,在红外区、可见光区、紫外区域的光子吸收性能更优异,光电导率更高,更有利于光生电子-空穴对的分离和迁移,即可以有效地提高其光电转换效率,其中掺杂La元素能更好地提高在红外区、可见光区及紫外区吸收光子的能力,更有利于光电转换的效率,提高导电性.     

Epitaxial films (Bi,Gd)3(Ga,Pt)2Ga3O12 grown by liquid-phase epitaxy

Single-crystal films of complex composition (Bi,Gd)₃(Ga,Pt)₂Ga₃O₁₂ on Gd₃Ga₅O₁₂(111) substrates are synthesized by liquid-phase epitaxy from a supercooled solution-melt based on Bi₂O₃-B₂O₃ flux. Optical absorption of Bi³⁺ and Pt³⁺ ions in these films is investigated in the wavelength range from 200 to 860 nm.     

掺杂晶体Cd0.35Hg0.65Ga2S4的光学特性

研究了掺杂非线性晶体Cd0.35Hg0.65Ga2S4的线性和非线性光学特性以及相位匹配.在相同的实验条件下，与已知的中红外晶体相比较，测定了该晶体的损伤阈值.实现了CO2激光二次谐波产生实验，与理论预测相一致. 关键词： 掺杂非线性晶体 Cd0.35Hg0.65Ga2S4 二次谐波产生 CO2激光     

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     

Luminescence and scintillation properties of YAG:Ce single crystal and optical ceramics

We use various techniques to study optical and scintillation properties of Ce-doped yttrium aluminum garnet, Y₃Al₅O₁₂ (YAG:Ce), in the form of a high-quality industrial single crystal. This was compared to optical ceramics prepared from YAG:Ce nanopowders. We present experimental data in the areas of optical absorption, radioluminescence, scintillation decay, photoelectron yield, thermally stimulated luminescence and radiation-induced absorption. The results point to an interesting feature—the absence of antisite (Y_Al, i.e. Y at the Al site) defects in optical ceramics. The scintillation decay of the ceramics is faster than that of the single crystal, but its photoelectron yield (measured with 1 μs integration time) is about 30-40% lower. Apart from the photoelectron yield value the YAG:Ce optical ceramic is fully comparable to a high quality industrial YAG:Ce single crystal and can become a competitive scintillator material.     

Ga and Pt NMR study of UPtGa5

^69,71Ga and ¹⁹⁵Pt NMR/NQR measurements have been carried out for the 5f-antiferromagnet, UPtGa₅. From a NMR study using a single crystal sample, Knight shift measurements are reported for two different Ga sites and for Pt. The principal axes of the electrical field gradient tensor at both Ga sites have been determined and the values of the splitting parameter ν_Q and the asymmetry parameter η have been evaluated. The hyperfine coupling constants with the external field along various directions are also reported for the two Ga sites and Pt.     

Physical properties of cage-like compound UB12

Boron and uranium form three metallic borides having the chemical formulae UB₂, UB₄ and UB₁₂. In this study, we present the temperature variations of magnetic susceptibility, specific heat, electrical resistivity (performed in magnetic fields of 0 and up to 9 T), thermoelectric power and thermal conductivity measured on the bulk sample of UB₁₂. This dodecaboride behaves as a typical metal, being a Pauli paramagnet and exhibiting a large variety of physical properties due to its specific close-packed structure containing B₁₂ groups. We describe also an uncommon phenomenon observed in UB₁₂, that is, a fairly large scattering of the experimental resistivity data under application of a magnetic field at low temperatures and its systematic vanishing during heating of the sample. This effect is probably caused by inharmonious movement (rattling) of the uranium atoms inside the oversized coordination cage, B₂₄, reflected by applying the magnetic field. The specific heat, resistivity, thermoelectric power and heat transport data have been analysed in the framework of the low-frequency Einstein modes, which are mainly responsible for the phonon spectra behaviour in the system studied here.     

Magnetic properties of CePd2Ga3

Field dependent specific heat measurements and a study of elastic neutron scattering experiments characterize CePd₂Ga₃ as a ferromagnetic Kondo compound with ordering in the basal plane belowT _C 6 K. The crystal field ground state of cerium in this hexagonal compound is the |±1/2> eigenstate. In the scope of a phenomenological model, the coupling constant and the Kondo temperature have been deduced.     

Efficient laser operation of Yb:Lu3Ga5O12 garnet crystal

Efficient laser operation is demonstrated at room temperature with a new Yb:Lu3Ga5O12 garnet crystal. A continuous-wave output power of 5.36 W is generated at a center oscillation wavelength of 1041 nm, with an optical-to-optical efficiency of 51% and the slope efficiency of 63%. In passively Q-switched operation, the maximum average output power reaches 4.0 W (center wavelength of 1034 nm) at a repetition rate of 71 kHz, with optical-to-optical and slope efficiencies measured to be 40% and 50%, respectively. Laser pulses of 26 ns duration are generated with a pulse energy of 91 μJ and peak power of 3.5 kW.     

La3Ga5SiO14晶体的介电性质、弹性与压电性质

研究了La3Ga5SiO14晶体的介电性质、弹性和压电性质，其中弹性和压电性质是利用高频振动模式通过谐振法测定的. 关键词： 介电性质 弹性 压电性质     

57Fe NMR in Y3Fe4.5Ga0.5O12 single crystal

The angular dependence of the⁵⁷Fe NMR spectra in a single crystal of Ga substituted YIG is studied with special attention paid to the satellite lines of the octahedral iron. These satellites correspond to ferric ions in the neighbourhood of which the Ga³⁺ ion is located. The anisotropy of the hyperfine field of these satellites is in accord with the prediction of the independent bond model. A simple analysis indicates that the main source of the anisotropy, besides the dipolar interaction, is the change of the supertransferred part of the hyperfine field.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.     

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.     

Anti-ferromagnetic ordering and crystal electric field in Ce:GSAG and Ce:LLGG garnets

The magnetic susceptibility of Ce:Gd₃Sc₃Al₃O₁₂ (Ce:GSAG) and Ce:La₃Lu₂Ga₃O₁₂ (Ce:LLGG) has been studied in the temperature range from 15 to 293 K. Both the Ce-doped garnets Ce:GSAG and Ce:LLGG show anti-ferromagnetic ordering at 18 and 27 K, respectively. Crystal electric field split energy levels have been used to calculate the magnetic susceptibility following Van Vleck's model. The calculated susceptibility values reasonably agree with the experimental susceptibility data of Ce:LLGG but differ for that of Ce:GSAG system. Contribution from long-range ordering between Ce and Gd ions for anomaly in Ce:GSAG system is speculated.     

Synthesis and luminescence properties of Er3+-doped Lu3Ga5O12 nanocrystals

The concentration-dependent luminescence properties of sol–gel-derived nanocrystalline Lu_3(1?x)Er_3xGa₅O₁₂ powders (where x=0.01, 0.05 and 0.1) have been studied. Laser-excited luminescence spectra, emission decays and upconversion luminescence of Er³⁺-doped Lu₃Ga₅O₁₂ nanocrystalline samples have been measured. The decay curve of the (²H_11/2,⁴S_3/2) emission exhibits a non-exponential behavior presumably due to cross-relaxation process. Moreover, near-infrared to visible upconversion luminescence has been observed in the green region for 1.0 mol% Er³⁺ ions in Lu₃Ga₅O₁₂ nanocrystals upon 815 nm excitation. The power dependence of the anti-Stokes luminescence suggests that upconversion is probably achieved through the sequential absorption of two photons. To the best of our knowledge, this is the first report on the preparation and optical properties of Er³⁺-doped Lu₃Ga₅O₁₂ in the form of nanocrystalline powders.