Curie temperatures of Y3Fe5O12/Gd3Fe5O12 superlattices

The magneto-optical Kerr effects (MOKE) of epitaxial Y₃Fe₅O₁₂/Gd₃Ga₅O₁₂ (YIG/GGG) garnet superlattices grown on (1 1 1)GGG previously by pulsed laser deposition (PLD) were measured. A series of superlattices were investigated with the thickness of the ferrimagnetic YIG layer varied from six unit cells to only one unit cell while keeping the Curie paramagnetic GGG fixed at one unit cell. It was demonstrated that the ellipsometric technique employing photoelastic modulators (PEM) is sensitive enough to measure the MOKE signals of these ultrathin oxide samples. The Curie temperatures, determined by MOKE, are fit with a power law, yielding a shift exponent λ = 3.1 ± 1.2.     

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.     

Laser-active colour centres with functional periodic structures in LiF fabricated by two interfering femtosecond laser pulses

We report a new technique to fabricate both laser-active F₂ and F₃⁺ colour centres in lithium fluoride and permanent periodic gratings with fringe spacings as fine as sub-micron size simultaneously by two interfering infrared femtosecond (fs) laser pulses. In particular, the optical properties of such colour centres produced by a single fs laser pulse are compared with those created by damage from radiation such as X-rays. Moreover, the present technique is applied to the first production of three-dimensional active channel waveguide and a pulsed distributed-feedback (DFB) laser at around 700 nm in LiF containing F₂ colour centres with fine-pitched micro-grating structures.     

Er3+/Yb3+共掺Gd3Sc2Ga3O12晶体的上转换发光

研究了提拉法生长的Er3+/Yb3+:Gd3Sc2Ga3O12和Er3+:Gd3Sc2Ga3O12晶体在室温下320-1700 nm范围的吸收光谱和500-750 nm范围内的上转换荧光谱,同时对其上转换荧光的可能发生机制、途径以及上转换过程可能对Er3+的2.8 μm波段激光振荡产生的影响进行了分析和讨论.结果表明:Yb3+的敏化显著地增强了晶体在966 nm附近的吸收能力,大幅度加宽了晶体在该处的吸收带宽.在940 nm激光的激发下,Er3+/Yb3+:Gd3Sc2Ga3O12中的上转换荧光强度明显强于Er3+:Gd3Sc2Ga3O12中的上转换荧光强度,表明Yb3+与Er3+之间存在高效率的能量传递,其主要上转换机制可能为Yb3+-Er3+,Er3+-Er3+能量传递.     

Infrared spectroscopy and lattice dynamical calculations of Gd3Al5O12, Tb3Al5O12 and Lu3Al5O12 single crystals

The infrared (IR) reflectance spectra of Gd₃Al₅O₁₂, Tb₃Al₅O₁₂ and Lu₃Al₅O₁₂ single crystals are studied for the first time. At room temperature, 15 infrared active modes for Lu₃Al₅O₁₂ and 14 for Gd₃Al₅O₁₂, Tb₃Al₅O₁₂, out of the 17 theoretically predicted, have been experimentally recorded. The complex dielectric function the refractive index, the absorption coefficient as well as the longitudinal (ω_LO) and transverse (ω_TO) frequencies of the long-wavelength T_1u modes are determined by the Kramers-Kronig transformation of the reflectance spectra. The experimental data are compared and discussed with the theoretical results obtained by the rigid ion model. Our theoretical analysis reveals that the bonds in the tetrahedra exhibit a covalent character while those in the dodecahedra almost ionic character, which is in accordance with the results for other materials of this crystal family.     

Thermal studies of the spin liquid state and analog to the He melting curve in a geometrically frustrated magnet

Gadolinium gallium garnet, Gd₃Ga₅O₁₂ (GGG) has an extraordinary low-temperature phase diagram. Although the Curie–Weiss temperature of GGG is −2 K, GGG shows no long-range order down to T0.4 K. At low temperatures GGG has a spin glass phase at low fields (0.1 T), a field-induced long-range ordered antiferromagnetic state at fields of between 0.7 and 1.3 T, and, at intermediate fields, an apparent spin-liquid state without long-range order. We have characterized the intermediate field (IF) state through heat capacity, thermal conductivity, and magnetocaloric measurements. Our results show a sharp high-field phase boundary of the thermal irreversibility of the spin glass phase of GGG implying that the intermediate field phase is distinct from the spin glass. The lower field boundary of the AFM phase is shown to have distinct minimum at T0.2 K, in analogy to the minimum in the melting curve of ⁴He. The existence of such a minimum is confirmed by measurements of the latent heat of the transition below that temperature.     

Low temperature spin dynamics of the geometrically frustrated antiferromagnetic garnet Gd3Ga5O12

The low temperature spin dynamics of the geometrically frustrated antiferromagnet Gd 3Ga 5O (12) (GGG) have been investigated using muon spin relaxation. No evidence for static order is seen down to a temperature of 25 mK or a few percent of the Curie-Weiss temperature. Instead there is a linear decrease in the Gd spin fluctuation rate below 1 K which extrapolates to a small but finite value of 2 GHz at zero temperature. In terms of the spin fluctuations the system appears essentially to remain dynamic at low temperatures (T>0.02 K) and magnetic fields up to 1.8 T.     

Gd3Ga5O12:Ag薄膜电致发光材料的制备及其发光性质

研究了Gd3 Ga5O12 :Ag材料的制备及其发光性质 .Gd3 Ga5O12 :Ag材料通过固相反应法制得 ,采用X射线衍射法分析了材料的结晶度及成分 .用电子束蒸发将该材料制备成交流的薄膜电致发光器件 ,得到了较好的蓝紫色发光 ,发光峰分别位于 397和 46 7nm .通过对材料的光致发光和激发光谱的研究和比较 ,得出 397和 46 7nm分别来自于氧空位和Ag 的发光 .     

Distortion of the Ligand Environment of Gd3+ and Eu2+ Ions in Garnets: Y3Al5O12, Lu3Al5O12, and Y3Ga5O12

Physics of the Solid State - Using experimental second-rank parameters of the spin Hamiltonian of the rhombic centers Gd3+ and Eu2+ in three garnets and the superposition approximation...     

Planar spin fluctuations with a quadratic thermal dependence rate in spin liquid Gd3Ga5O12

The spin liquid properties of Gd3Ga5O12 have been examined using 155Gd M?ssbauer spectroscopy down to 0.027 K. Information has been obtained concerning both the directional properties of the short range correlated moments and the thermal dependence of their spin fluctuation rates. Each Gd3+ spin (S=7/2) is found to be confined to a plane and its fluctuation rate decreases from approximately 2.8 x 10(9) s(-1) at 0.4 K to approximately 0.03 x 10(9) s(-1) at 0.09 K following a close-to-quadratic thermal dependence.     

Induced absorption in yttrium aluminium perovskite crystals irradiated by 12C and 235U ions

The present work is devoted to investigation of optical absorption in pure and neodymium-doped YAlO₃ (YAP) single crystals in the spectral range 0.2–1.1 μm induced by the influence of ¹²C ions irradiation with energy 4.50 MeV/u (MeV per nucleon) and a fluence 2 × 10⁹ cm^?2 or of ²³⁵U ion irradiation with energy 9.35 MeV/u and a fluence 5 × 10¹¹ cm^?2. The induced absorption in the case of ¹²C ions irradiation is caused by recharging of point growth defects and impurities under the radiation influence. After irradiation by ²³⁵U ions with fluence 5 × 10¹¹ cm^?2 the strong absorption rise is probably caused by contribution of the lattice destruction as a result of heavy ion bombardment.     

Energy Spectra of the Tunable Laser Crystal Gd3Ga5O12:Cr3+ and Their Pressure-Induced Shifts

By means of both the theory for pressure-induced shifts(PS) of energy spectra and the theory for shifts of energy spectradue to electron-phonon interaction (EPI), at 300 K,the `pure electronic' contributions andthe contributions from EPI to R₁ line, R₂ line, and U band ofGGG:Cr³⁺ as well as their PS have been calculated, respectively.The total calculated results are in good agreement with all theexperimental data. Their physical origins have been explained.It is found that the mixing-degree of |t₂²(³T₁)e⁴T₂> and |t₂³²E> base-wavefunctions in the wavefunctions of R₁ level of GGG:Cr³⁺ is considerableunder normal pressure, and the mixing-degree rapidly decreaseswith increasing pressure. The change of the mixing-degree withpressure plays a key role for PS of R₁ line or R₂ line. At300 K, both the temperature-independent contribution to R₁ line(or R₂ line or U band) from EPI and the temperature-dependent oneare important. The remarkable difference between pressure-dependentbehaviors of PS of R₁ lines of GGG:Cr³⁺ and GSGG:Cr³⁺ resultsfrom the differences of their microscopic properties. The featuresof emission spectra of GGG:Cr³⁺ at various pressures have satisfactorilybeen explained.     

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)     

YAG晶体色心的EPR谱

本文描述了8种YAG样品的室温和77K的EPR谱.从这些谱的参数与光谱的实验数据对照,认为晶体中有三种顺磁性的色心,其中g～2.00和g～1.98两条顺磁谱相应于光谱2×10~4cm~(-1)～3.4×10~4cm~(-1)的吸收带,为YAG基质晶体中的缺陷俘获一个电子构成的电子型缺陷中心;而 g～30.60的顺磁谱线与氧空位和掺杂的金属离子Mg~(2+) 、Cr~(3+)有关,推测为氧空位团或氧空位与金属离子构成的S>1/2的复合顺磁中心缺陷.YAG晶体随着在大气氛中高温退火,氧的进入和金属离子的掺入,造成电子和空间体积的不平衡,从而使晶体色心浓度加大.