Growth of Nd:Sr3Ga2Ge4O14 crystals by a modified Bridgman method

Bridgman growth of Nd:SGG (Sr₃Ga₂Ge₄O₁₄) crystals has been investigated for the first time. Pt crucible of ∅︁25mm×250mm with a seed well of ∅︁10mm×80 mm is used, and seed is SGG crystal of ∅︁10mm×50mm grown by Bridgman method in advance. The growth parameters are optimized as the furnace temperature is set to 1450∼1500°C, temperature gradient in the crystal‐melt interface is less than 25 K/cm and growth rate is less than 0.5mm/h. The Nd:SGG crystals with 25mm in diameter and 60mm in length are grown successfully from 1.5 to 8at% Nd³⁺ doped stoichiometric Sr₃Ga₂Ge₄O₁₄ melt. The distribution coefficient and concentration of Nd³⁺ in Nd:SGG crystals are obviously higher than those of Nd:YAG crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nd3+:Sr3Ga2Ge4O14晶体的生长及吸收光谱

采用坩埚下降法生长了Nd3+掺杂浓度分别为15;、8;和2.5;原子分数的Sr3Ga2Ge4O14晶体,所得晶体最大尺寸为φ26mm×15mm.Nd3+掺杂Sr3Ga2Ge4O14晶体的特征吸收峰波长为806nm,与Nd3+离子在YAG中的特征吸收峰相比,向短波方向发生了微小的偏离.这是Sr3Ga2Ge4O14晶格中Ga3+和Ge4+的统计分布所致.Nd3+:SGG晶体的这些特性将有助于泵浦效率的提高和泵浦阈值的降低,因此Nd3+:SGG晶体有望成为一种新型的LD泵浦固体激光材料.     

新型压电晶体Sr3 Ga2 Ge4 O14的性能表征

采用坩埚下降法以及坩埚密封技术,成功生长了直径50mm的新型压电晶体Sr3Ga2Ge4O14.测试了晶体的晶格常数、热膨胀系数、密度、硬度和透过光谱等基本物理性能.测试结果表明:晶体热膨胀系数明显小于石英晶体,而且α11和α33相对比较接近,有利于该晶体用作声表面波用基片材料.在250～2500nm波段范围内,其透过率均大于80;,优于相同结构的La3Ga5SiO14晶体,是一种潜在的激光基质晶体材料.     

Spectroscopy studies of pure and chromium-doped calcium gallogermanate crystals, Ca3Ga2Ge4O14

Absorption spectra, the spectra of circular dichroism and magnetic circular dichroism of pure and Cr-doped Ca₃Ga₂Ge₄O₁₄ crystals have been studied. The crystal-field parameters and the transition frequencies of Cr³⁺ ions are calculated. The location of Cr³⁺ and Cr⁴⁺ ions in oxygen octahedra and tetrahedra is confirmed. The spectra of circular dichroism show the maxima due to Cr³⁺ ions and growth-induced defects.     

Sr3Ga2Ge4O14∶Eu3+,Bi3+粉体的光谱特性及能量传递研究

研究了Eu3和Bi3+共掺锗酸镓锶粉体的合成、结构及其光谱性能.结果表明,合成粉体为纯三方相结构,掺杂没有引起新相生成,表明部分无序结构为掺杂离子提供更大的包容空间,从而实现激活离子的高浓度掺杂.高温固相合成的粉体在蓝绿光区域(570～700 nm)具有丰富的发射峰,其主峰位于618 nm,是Eu3处于非对称中心格位产生的特征峰,由此说明Eu3+取代Sr2+的位置;当Eu3+的掺杂浓度为15mol;时,在618 nm处发光强度达到最大.掺Bi3+明显增强了Eu3+的发光,是一种有效的敏化剂;当Bi3+掺杂量为5mol;时,Eu3+的相对发光强度同比提高了51.3;.     

Influence of rare-earth impurities on the Ge and Ga local structure in the Ca3Ga2Ge3O12 glass

The present contribution presents X-ray absorption fine structure (XAFS) measurements and analysis of the Ge and Ga local structure in glass of Ca₃Ga₂Ge₃O₁₂ composition, doped with rare-earth metals (Ce, Eu, Ho, Er in the amount of 0.7 wt% and Nd in the amount of 1.0 wt%). The Ge and Ga ion neighborhoods in the considered glass samples have been compared with data obtained for undoped glass. The results have shown that introduction of rare-earth ions modifies the local structure around the Ga ions in the glass network, leaving the same occurrence ratio of the GaO₄ and GaO₆ structural units as in undoped Ca₃Ga₂Ge₃O₁₂ glass. At the same time, the GeO₂ subsystem remains completely unaffected by the presence of rare-earth dopants.     

Accurate crystal-structure refinement of Ca3Ga2Ge4O14 at 295 and 100 K and analysis of the disorder in the atomic positions

The accurate X-ray diffraction study of a Ca₃Ga₂Ge₄O₁₄ crystal (sp. gr. P321, Z = 1) has been performed using repeated X-ray diffraction data sets collected on a diffractometer equipped with a CCD area detector at 295 and 100 K. The asymmetric disorder in the atomic positions in Ca₃Ga₂Ge₄O₁₄ is described in two alternative ways: with the use of anharmonic atomic displacements (at 295 K R/wR = 0.68/0.60%, 3754 reflections; at 100 K R/wR = 0.90/0.70%, 3632 reflections) and using a split model (SM) (at 295 K R/wR = 0.74/0.67%; at 100 K R/wR = 0.95/0.74%). An analysis of the probability density function that defines the probability of finding an atom at a particular point in space shows that, at 295 K, five of the seven independent atoms in the unit cell are asymmetrically disordered in the vicinity of their sites, whereas only three atoms are disordered at 100 K. At both temperatures the largest disorder is observed at the 3f site on a twofold axis, which is a prerequisite for the formation of helicoidal chains of atoms along the c axis of the crystal and can serve as a structural basis for multiferroic properties of this family of crystals with magnetic ions.     

Growth,structure, and superconducting properties of Bi2Sr2Ca2Cu3O10 and (Bi,Pb)2Sr2Ca2Cu3O10‐y crystals

Large and high‐quality single crystals of both Pb‐free and Pb‐doped high temperature superconducting compounds (Bi_1‐xPb_x)₂Sr₂Ca₂Cu₃O_10‐y (x = 0 and 0.3) were grown by means of a newly developed “Vapour‐Assisted Travelling Floating Zone” technique (VA‐TSFZ). This modified zone‐melting technique was realised in an image furnace and allowed for the first time to grow Pb‐doped crystals by compensating for the Pb losses occurring at high temperature. Crystals up to 3×2×0.1 mm³ were successfully grown. Post‐annealing under high pressure of O₂ (up to 10 MPa at T = 500°C) was undertaken to enhance T_c and improve the homogeneity of the crystals. Structural characterisation was performed by single‐crystal X‐ray diffraction (XRD) and the structure of the 3‐layer Bi‐based superconducting compound was refined for the first time. Structure refinement showed an incommensurate superlattice in the Pb‐free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 27.105(4) Å, b = 5.4133(6) Å and c = 37.009(7) Å. Superconducting studies were carried out by A.C. and D.C. magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (ΔT_c ≤ 1 K). In optimally doped Pb‐free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2�10⁵ A/cm² were measured at T = 30 K and μ₀H = 0 T. A weak second peak in the magnetisation loops was observed in the temperature range 40‐50 K above which the vortex lattice becomes entangled. We have measured a portion of the irreversibility line (0.1‐5 Tesla) and fitted the expression for the melting of a vortex glass in a 2D fluctuation regime to the experimental data. Measurements of the lower critical field allowed to obtain the dependence of the penetration depth on temperature: the linear dependence of λ(T) for T < 30 K is consistent with d‐wave superconductivity in Bi‐2223. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The absorption and circular dichroism spectra of langasite family crystals doped with chromium ions

The absorption and circular dichroism spectra of langasite family crystals, La₃Ga₅SiO₁₄, La₃Ga₅GeO₁₄, Ca₃Ga₂Ge₄O₁₄, Sr₃Ga₂Ge₄O₁₄ (red), Sr₃Ga₂Ge₄O₁₄ (green), La₃Ta_0.5Ga_5.5O₁₄, and La₃Nb_0.5Ga_5.5O₁₄, which were doped with chromium ions, have been investigated in the range of 240–850 nm. It is shown that chromium ions are incorporated into the structure of the investigated crystals both in the octahedrally (Cr³⁺ ion in 1a octahedron) and tetrahedrally (Cr⁴⁺ ion in 2d tetrahedron) coordinated positions. The ion ratio Cr³⁺/Cr⁴⁺ changes in a wide range in the crystals studied.     

Czochralski growth and characterization of Dy: La3Ga5.5Nb0.5O14 single crystals

Dysprosium (Dy) doped La₃Ga_5.5Nb_0.5O₁₄ single crystals were grown by the traditional Czochralski method along z‐axis. The structure of the crystal has been studied by X‐ray powder diffraction method, and the unit‐cell parameters are calculated to be a=8.22070 Å, c=5.12533 Å and V=299.965 ų. The segregation coefficient of Dy³⁺ in La₃Ga_5.5Nb_0.5O₁₄ crystal was measured by X‐ray fluorescence analysis. For 1 mol% doping level in the melt, the distribution coefficient of Dy³⁺ was determined to be 0.341 wt%. Specific heat, thermal expansion and transmission spectrum of Dy: La₃Ga_5.5Nb_0.5O₁₄ single crystals have been measured. The fluorescence spectra of Dy³⁺: La₃Ga_5.5Nb_0.5O₁₄ crystals were measured at room temperature, and there were four emission transitions occurring at 479, 576, 662 and 754 nm, respectively. The fluorescent lifetimes measurement results show 1.0% Dy: La₃Ga_5.5Nb_0.5O₁₄ possesses shorter fluorescence decay time (303.4 μs) than does 1.0%Dy:LGS (436.12 μs). (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

EPR spectra of irradiated Na2Cr2O7 · 2 H2O crystals

The EPR spectra of X-irradiated Na₂Cr₂O₇ · 2 H₂O crystals grown from the aqueous solution at room temperature are studied. Three groups of lines are detected, which marked conventionally as C₁, C₂ and C₃. Each of the C₁ and C₂ line groups is a superposition of two doublets. The lines are interpreted as due to the Cr⁵⁺ ions in the distorted (stretched) oxygenous tetrahedron. The doublet structure is due to hyperfine interaction with nuclei of 1/2 spin which are protons of water. It is shown that the C₁ and C₂ line groups are due to the centers of the same type with different orientations in the lattice. The principal g-tensor values for these centres were as follows: g_z = 1.916, g_y = 1.978, g_x = 1.986.     

Cluster self-organization of TR,Ge-containing crystal-forming systems: Suprapolyhedral precursors and self-assembly of La3Ga[6]Ga 4 [4] Ge[4]O14 (langasite) and La3Ge[6]Ge 2 [5] Ge 2 [4] Ga[4]O16 gallogermanates

A combinatorial-topological analysis of the La₃Ga^[6]Ga ₄ ^[4] Ge^[4]O₁₄ and La₃Ge^[6]Ge ₂ ^[5] Ge ₂ ^[4] Ga^[4]O₁₆ gallogermanates, which have MT and MPT microporous frameworks composed of M octahedra (GeO₆, GaO₆), T tetrahedra (GeO₄, GaO₄), and P pyramids (GeO₅), is performed using the method of coordination sequences with the TOPOS 3.2 program package. It is established that the La₃Ga^[6]Ga ₄ ^[4] Ge^[4]O₁₄ gallogermanate is characterized by a crystal-forming net 6 6 6 (of the graphite type). A new type of the binodal net 6 10 1 0 + 6 10 (2: 1) is revealed in the La₃Ge^[6]Ge ₂ ^[5] Ge ₂ ^[4] Ga^[4]O₁₆ gallogermanate. The cyclic cluster precursors composed of six polyhedra with a lanthanum template atom at the center of the LaMT ₅ and LaMP ₃ T ₃ clusters are identified by the two-color decomposition of the nets in the structures of the La₃Ga^[6]Ga ₄ ^[4] Ge^[4]O₁₄ and La₃Ge^[6]Ge ₂ ^[5] Ge ₂ ^[4] Ga^[4]O₁₆ gallogermanates. The coordination numbers of the cluster precursors in these structures are found to be equal to 6 and 4 for two-dimensional nets and 8 and 6 for three-dimensional nets, respectively.     

Optics and spectroscopy of a Pb3Ga2Ge4O14:Nd3+ crystal, a new representative of the langasite family

Absorption and luminescent properties of a Pb₃Ga₂Ge₄O₁₄:Nd³⁺ crystal have been studied. The refractive indices are measured in the range from 0.405 to 1.064 μm, and the molecular refraction is calculated.     

Optical properties of Sr3TaGa3Si2O14 single crystal

The specific rotation ρ of strontium tantalum gallium silicate Sr₃TaGa₃Si₂O₁₄ (STGS) piezoelectric single crystal was determined from 350 to 850 nm by measuring the optical transmission between parallel polarisers in Z direction. It is shown that Sr₃TaGa₃Si₂O₁₄ has quite large a value of ρ which is a little smaller than that of strontium niobium gallium silicate Sr₃NbGa₃Si₂O₁₄ (SNGS). The crystal with ordered structure which is isostructural to calcium gallium germanate Ca₃Ga₂Ge₄O₁₄ (CGG) was grown by Czochraiski technique. And its birefringence was also determined. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of a new langasite‐type single crystal Sr3NbAl1.5Ga1.5Si2O14

Single crystals of Sr₃NbAl_1.5Ga_1.5Si₂O₁₄ (SNAGS) with langasite structure have been successfully grown by Czochralski method. The X‐ray diffraction (XRD) verified that the as‐grown crystal was isostructural with A₃BC₃D₂O₁₄ structure and the lattice parameters were calculated as follows: a = 8.242 Å, c = 5.041 Å, V = 296.6 ų. The piezoelectric coefficient d₁₁ was 5.7pC/N, which was 2.47 times of α‐quartz (d₁₁=2.31pC/N). The electric resistivity was up to 3.04×10⁶ Ωcm at 700 °C for X‐cut sample. In addition, the transmission spectrum of the SNAGS crystal showed that it had a high transmittance (>80%) in the range of 350‐800 nm and exceeded 90% above 520 nm. These results suggest that the SNAGS crystals have potential applications in high‐temperature piezoelectric sensors and optical techniques. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

溶胶-凝胶法制备Zn3Ga2Ge2O10:Cr3+0.01,Pr3+0.03,Yb3+0.3纳米长余辉材料及其表面修饰的研究

以Ga(NO3)3·8H2O、Zn(NO3)2·6H2O、Pr(NO3)2·6H2O、GeO2、Yb(NO3)3·5H2O、Cr(NO3)2·9H2O为原料,采用溶胶-凝胶法合成了Cr3+,Pr3+,Yb3+共掺杂的Zn3Ga2Ge2O10长余辉纳米材料(PLNPs).利用XRD,SEM,激发发射图谱,余辉曲线测试确定1000℃煅烧,保温3 h时,基质Zn3 Ga2 Ge2 O10已形成.Yb3+掺杂百分比为0.3时,样品的发光性能最好.Zn3 Ga2 Ge2 O10:Cr3+0.01,Pr3+0.03,Yb3+0.3纳米长余辉材料在波长为267 nm的紫外线激发下发射出中心波长为745 nm的深樱桃红色光,此时晶粒粒径约为150 nm;随着Yb3+掺杂百分比的增加,晶粒粒径逐渐变小.通过FT-IR,Zeta电势,激光粒度测试,TEM及悬浮实验测试表明,PEG修饰PLNPs后,可观察到明显的核壳结构,水合粒径约为155 nm;水溶性大大增加,0.3 mg/mL的浓度下其悬浮时间超过48 h,这表明PEG包裹PLNPs成功.     

EPR spectra of Cr3+-doped LuNbO4 crystals

Ferroelastic LuNbO₄ single crystals containing 0.3 at. % Cr³⁺ ions have been grown by the floating zone technique, and their EPR spectra have been studied at a frequency of 9.8 GHz at room temperature. The lines on the spectra are due to the transitions caused by three paramagnetic centers formed as a result of the replacement of one isovalent position of a Lu₃₊ ion and two nonisovalent positions of Nb₅₊ions by Cr₃₊-ions. As a result of twinning, the line number is doubled and four principal directions arise along which the same spectra are obtained. The spectra of these centers were described by a spin Hamiltonian with S = 3/2, the D and E parameters ranging from 0.024 to 0.17 cm^?1, and the g-factors g ∥ = 1.75–2.20 and g ⊥ = 1.90–2.13.     

Photoluminescence and radiation damage in W,Mg, Ca doped Bi4Ge3O12 crystals

Spectral properties and radiation damage in W, Mg and Ca doped Bi₄Ge₃O₁₂ (W:BGO, Mg:BGO, Ca:BGO) crystals before and after thermal treatment and gamma‐ray (γ‐) or ultraviolet (UV) radiation were studied. The absorption and the photoluminescence (PL) spectra of doped BGO crystals in visible region were measured. Before γ or UV radiation, the emission intensity of W:BGO crystal is stronger than that of pure BGO at about 500 nm. After γ radiation (10k Gy), the emission intensities of doped BGO are all weaker than pure BGO under identically condition. However, the emission intensity of W:BGO is stronger than that of pure BGO after UV exposure (10k Gy). Thermal treated (annealed in N₂ at 550 °C for 6 h) W:BGO has shown a much stronger emission intensity than others. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sr3NbGa3Si2O14压电晶体旋光性质的研究

本文测定了紫外、可见光区新型压电晶体-Sr3NbGa3Si2O14(SNGS) 的透过率,并利用一种新方法即通过测量晶体在平行偏振系统中的透过率谱研究了其旋光性,且拟合出旋光色散曲线.此晶体属左旋单轴晶体,旋光非常大,其旋光率ρ在513nm处达到43.69°/mm.     

Absorption and circular-dichroism spectra of iron-doped berlinite crystals

Absorption and circular-dichroism spectra of iron-doped AlPO₄ crystals have been studied. For the first time, the experimental data on the electronic states of the [FeO₄]^5? complex are obtained in the range from 190 to 350 nm with due regard for the interactions that cannot be described within the one-electron approximation. The bands observed in the absorption and circular-dichroism spectra are attributed to corresponding electronic transitions. The advantages of the use of crystal-field-induced circular dichroism in comparison with other spectroscopic methods in the analysis of the electronic states of impurity ions in gyrotropic crystalline matrices are considered on the [FeO₄]^5? complex.