Luminescence of enrichment centers in yttrium-aluminum garnet crystals

The spectrum of enrichment centers in yttrium-aluminum garnet crystals is studied. Analysis of the photoluminescence and excitation spectra together with measurements of luminescence kinetics allow establishment of the energy structure of the centers found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 83–87, January, 1984.     

Study of sensitization of Cr4+ ions by Yb3+ ions in yttrium-aluminum garnet crystals

The possibility of using ytterbium ions as sensitizers of luminescence of tetravalent chromium in yttrium-aluminum garnet single crystals is studied. It is found that average values of the microparameters of electronic energy transfer between ytterbium and chromium ions are C _DA=7.05×10^?36 cm⁶/s and C _DD=4.55×10^?43 cm⁶/s.     

Pulsed cathodoluminescence of yttrium-aluminum garnet in the visible spectral range

The spectra of the pulsed cathodoluminescence of yttrium-aluminum garnet (YAG) laser crystals activated with various impurities (YAG:Nd; YAG:Nd,Ce; YAG:Cr; YAG:Cr,Ce; YAG:Er; and YAG:Sm) are studied. The bands of the rare-earth ions in the visible spectral range are identified. Luminescence of Ce²⁺ ion is revealed in the YAG:Cr,Ce crystal. Original Text ? Astro, Ltd., 2006.     

Determination of the position of impurity atoms in yttrium-aluminum garnet by means of forbidden reflections

The possibility of determining the position of terbium impurity atoms in yttrium-aluminum garnet lattice is analyzed. It is shown that in the presence of the impurity in both aluminum and yttrium positions the tensor factors of the nearest yttrium atoms change. To determine the position of impurity atoms in the yttrium-aluminum garnet unit cell, measurements should be carried out at energies near the L-absorption edges of terbium.     

Luminescence and absorption of divalent ytterbium ion in yttrium-aluminum garnet ceramics

Strong absorption bands at 280, 385, and 640 nm; a pulsed cathodoluminescence band with peaks at 325 and 520 nm and a dip at 385 nm; and a structured luminescence band in the range of 591–711 nm composed of four pair lines and having a dip near 640 nm have been observed in the spectra of yttrium-aluminum garnet ceramics activated with ytterbium (10 mol %) and subjected to vacuum sintering at a temperature of 1800°C. It is shown that these spectral features are absorption and luminescence bands of divalent ytterbium ions with the 4f ¹³6s electron configuration of the ground state. These ions occupy the cubic site that is formed under conditions of oxygen deficit and disappears when the latter is removed during annealing ceramics in air.     

钇铝石榴石在高压下的光学性质第一性原理研究

本文采用基于密度泛函理论(DFT)的第一性原理方法,分别计算了120 GPa的压力范围内钇铝石榴石理想晶体和含氧空位点缺陷晶体的光学性质.计算数据表明:(1)在120 GPa的压力范围内其理想晶体和含2+价氧离子空位(形成能最低)的缺陷晶体在可见光区不存在光吸收(是透明的).(2)压力加载将导致其反射谱峰值强度降低,且空位缺陷的存在使其峰值强度进一步减弱.这些结果对进一步实验有重要的参考价值.     

Determining spatial structures of ion crystals by simulated annealing method

Calculating the spatial structures of ion crystals is important in ion-trapped quantum computation. Here we demonstrate that the simulated annealing method is a powerful tool to evaluate the structures of ion crystals. By calculating equilibrium positions of 10 ions under harmonic potential and those of 120 ions under anharmonic potential, both with the standard procedure and simulated annealing method, we find that the standard procedure to evaluate spatial structures is complicated and may be inefficient in some cases, and that the simulated annealing method is more favorable.     

Determining the sum of flexoelectric coefficients in nematic liquid crystals by the capacitance method

A detailed theoretical analysis of determining the sum of flexoelectric coefficients in nematic liquid crystals using the capacitance method is given. In the strong anchoring parallel aligned nematic （PAN） and hybrid aligned nematic （HAN） cells, the dependences of the capacitance on the sum of flexoelectric coefficients and the applied voltage are obtained by numerical simulations, and the distributions of the director and the electric potential for different applied voltages and flexoelectric coefficients are also given. Based on this theoretical analysis, we propose an experimental design for measuring the capacitance of a liquid crystal cell using the improved precision LCR meter E4980A （Agilent）. Through comparing the experimental data with the simulated results, the sum of flexoeletric coefficients can be determined.     

Luminescence centers in thin films of yttrium oxide and yttrium-aluminum garnet activated with bismuth

Luminescence spectra and photoluminescence excitation spectra of Y₂O₃:Bi and Y₃Al₅O₁₂:Bi thin films were investigated. Luminescence was stimulated by the emission from two types of centers that were associated with the substitution of Bi³⁺ for Y³⁺ in sites of the crystal lattice of Y₂O₃ (Y₃Al₅O₁₂) with point symmetries C₂ and C_3i (D₂ and C_3i). The emission of Bi³⁺ in the site with point symmetry C_3i causes blue luminescence in both Y₂O₃:Bi and Y₃Al₅O₁₂:Bi films with maxima at 3.03 eV and 3.15 eV, respectively, that is related to the ³P₁-¹S₀ transition. The emission of Bi³⁺ in the site with point symmetry C₂ gives green luminescence in Y₂O₃:Bi with the maximum at 2.40 eV that is also related to the ³P₁-¹S₀ transition. The emission of Bi³⁺ in the site with point symmetry D₂ leads to ultraviolet luminescence in Y₃Al₅O₁₂:Bi with the maximum at 3.75 eV that corresponds to the ³P₁-¹S₀ transition. The red luminescence band with the maximum at 1.85 eV in Y₂O₃:Bi is due to the presence of structural defects. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 202–207, March–April, 2008.     

Nonempirical cluster calculations of the electric field gradient tensor in yttrium-aluminum garnet Y3Al5O12

The electric field gradient (EFG) tensor at the aluminum nucleus sites in yttrium-aluminum garnet Y₃Al₅O₁₂ is calculated using the Hartree-Fock method and the nonempirical cluster approach. It is shown that the EFG tensor at the Al_tetr sites is described well taking into account the nearest neighbors (an [AlO₄]^?5 cluster), whereas for the Al_oct sites the effect of more distant ions is important. The results are compared with the available experimental data and the results of band calculations.