Crystal growth and defects in Ga3PO7 crystals

Crystals with a non‐centrosymmetric structure are of great interest owing to their properties such as ferroelectricity, piezoelectricity, dielectric behavior and optical properties. In this letter, Ga₃PO₇ crystals are grown by the top‐seeded solution growth (TSSG) method from a Li₂O‐3MoO₃ flux. It crystallizes in a non‐centrosymmetric trigonal crystal system with space group R3m within point group 3m. The growth defects are investigated by means of chemical etching method. The results reveal hot concentrated phosphoric acid to be a good etchant for Ga₃PO₇. The main defects are cracks, inclusions, dislocations and twin. In the meantime, the effective measures for reducing the defects are proposed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectroscopic properties of La3Ga5SiO14:Er3+ (1%) crystals

Single crystals of Erbium (Er) doped La₃Ga₅SiO₁₄ (LGS) have been grown along c‐axis by using the Czochralski method. The absorption and fluorescence spectra of LGS: Er³⁺ single crystals have been measured and analyzed according to the Judd‐Ofelt theory. When applied, the following spectral parameters have been obtained: intensity parameters Ω_t, Ω₂= 2.741674×10^‐20cm², Ω₄= 0.66934×10^‐20 cm² and Ω₆= 0.592591×10^‐20 cm², radiative transition probabilities A_J,J”, P_J,J”. The radiative lifetime of levels ⁴I_13/2, ⁴H_9/2, ⁴S_3/2 are 11.333ms, 0.447ms and 0.704ms, respectively. The fluorescence branching ratios and the integrated emission cross sections are also calculated. The results suggest that LGS: Er crystals have potential applications as a laser material. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

零声表面波频率温度系数方向的硅酸镓镧晶体生长

采用提拉法生长了高质量、大尺寸、结构完整的声表面波零温度系数切向LGS晶体.XRD图谱显示,生长的晶体为单一相LGS晶体,晶格常数为a=0.816274 nm,c=0.509253 nm,密度为5.7463 g/cm3.压电常数、介电常数、热膨胀性能等与传统方向生长的晶体一致.用此方向生长的LGS晶体制作声表面波频率温度性能优化的切片,只需要垂直生长方向进行切割,可以大大简化晶体的加工工艺、提高LGS晶体的利用率,节省材料成本.     

Growth and characterization of pure and Co2+‐doped Li2B4O7 single crystals

Pure and Co‐doped Li₂B₄O₇ (LBO) single crystals were grown by the Czochralski method. Starting concentrations of Co₂O₃ in the melt were: 0.5, 0.85 and 1 mol% relative to Li₂CO₃. Technological factors affecting the quality of both crystals were discussed. Optical absorption and EPR spectra were analyzed to define the oxidation states and lattice sites of cobalt ions. It was shown that Co²⁺ ions enter LBO crystal at octahedral Li⁺ site positions. Low‐temperature EPR measurements revealed that two types of Co²⁺ complexes can be distinguished in the Li₂B₄O₇:Co crystals. Additional absorption calculated for γ‐irradiated crystals showed V_k type defects suggesting the creation of cation vacancies during growth. The concentration of the defects decreases with an increase of intentional Co concentration. Introduction of cobalt ions to LBO crystal is limited probably by the formation of cobalt ion pairs or by the entrance of cobalt as Co⁺. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

Growth and optical damage resistance of Sc,Er Co‐doped LiNbO3 crystals

A series of Sc:Er:LiNbO₃ crystals have been grown by Czochralski method. Their ultraviolet‐visible (UV‐Vis) absorption spectra was measured and discussed to investigate their defect structure. The optical damage resistance of Sc:Er:LiNbO₃ crystals was characterized by the transmitted beam pattern distortion method. It increases remarkably when the concentration of Sc₂O₃ exceeds a threshold concentration. The optical damage resistance of Sc (3.0mol %):Er:LiNbO₃ is much higher than that of the Er:LiNbO₃. The intrinsic and extrinsic defects were discussed to explain the enhance of the optical damage resistance in the Sc:Er:LiNbO₃ crystals. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electro‐optic,Piezoelectric and Dielectric Properties of Langasite (La3Ga5SiO14), Langanite (La3Ga5.5Nb0.5O14) and Langataite (La3Ga5.5Ta0.5O14)

Refractive indices were determined of single crystals of La₃Ga₅SiO₁₄ (langasite, LGS), La₃Ga_5.5Nb_0.5O₁₄ (langanite, LGN) and La₃Ga_5.5Ta_0.5O₁₄ (langataite, LGT) in the wavelength region between 0.36 μm and 2.33 μm. While phase‐matched optical second harmonic generation is not possible in LGS it occurs in the isotypic compounds LGN and LGT. Temperature‐dependent examination of the dielectric properties of LGS up to 600 °C showed anomalous behaviour. For all three substances the electro‐optic [r^σ_ijk] (“unclamped”) and the piezoelectric [d_ijk ] tensors were determined at room temperature. In addition, the temperature‐dependence of these properties was studied for LGS between –200 °C and +200 °C by a Jamin interferometer in combination with a modified Sénarmont compensator.     

Investigation of nucleation kinetics and crystal defects of HMX

The nucleation kinetics of HMX (cyclotetramethylene tetranitramine, C₄H₈N₈O₈) in γ‐butyrolactone was studied in cooling process by induction time method. The laser scattering method was used to measure the solubility data and metastable region of HMX in γ‐butyrolactone. The induction time was measured over a range of supersaturation at different temperatures. Then, the nucleation mechanism of HMX in γ‐butyrolactone was investigated by analysis the relationships between induction time and supersaturation. The results indicated homogeneous nucleation dominated at high supersaturation of S >1.35, while the heterogeneous nucleation dominated at low supersaturation of S < 1.35. The values of interfacial tension at different final temperatures were calculated to indicate the ability of HMX to be crystallized. The growth mechanism of HMX was investigated by the data fitting applying different growth mechanism models and identified as two‐dimensional nucleation‐mediated (2D) growth. Finally, the effects of supersaturation and temperature on the crystal defects were analyzed based on the nucleation kinetics. When the temperature is below 303.15K, homogeneous nucleation dominated the nucleation process at higher supersaturation. Fine HMX crystals with more defects were produced. On the contrary, heterogeneous nucleation mechanism dominated at lower supersaturation. large regular HMX crystals with fewer defects were formed when the temperature is above 318.15K.     

Structure and Photo‐Damage Resistance of Li‐Rich LiNbO3 Crystals Co‐Doped with Zn2+/Er3+

The pure congruent LiNbO₃, Er:LiNbO₃ and Zn,Er co‐doped Li‐rich LiNbO₃ crystals were grown by Czochralski method. The X‐ray diffraction method and ultraviolet‐visible absorption spectra of the crystals were used to analyze the structure of the crystals. The photo‐damage ability resistance of the crystals was measured. The Zn,Er co‐doped Li‐rich LiNbO₃ crystals show a decrease in lattice constant values, a shift in absorption edge of ultraviolet‐visible absorption spectra towards shorter wavelength, and three orders of magnitude increase in photo‐damage resistance compared to congruent LiNbO₃ crystal. The intrinsic and extrinsic defects are discussed to explain the enhance of the photo‐damage ability resistance     

The influence of Yb3+ concentration on Yb:YAl3(BO3)4

The Yb:YAl₃(BO₃) ₄ crystals with different Yb³⁺ doping concentration have been grown by the flux method. The lattice parameters and decomposition of the Yb:YAl₃(BO₃)₄ crystal with different Yb³⁺ doping concentration were measured by X‐ray and DTA method. The transmission and fluorescence spectra of Yb³⁺:YAl₃(BO₃)₄ crystal have been measured. The growth defects of Yb_xY_1‐xAl₃(BO₃)₄ crystals were also detected by using the chemical etching method. The results show that the ytterbium concentration influences these properties of Yb:YAl₃(BO₃)₄. As the Yb³⁺ concentration increased, the crystal lattice parameter was decreased. At high doping level, the absorption peak concerned at about 980 nm shift to short wavelength. It is also found that the perfection of Yb:YAl₃(BO₃) ₄ crystal with low Yb³⁺ doping concentration is better than that with high Yb³⁺ concentration. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microstructure and optical properties of Zn:Mn:Fe:LiNbO3 crystals

Zn:Mn:Fe:LiNbO₃ crystals were prepared by Czochralski technique. Its microstructure was measured and analyzed by UV‐Vis absorption spectra. The optical damage resistance of Zn:Mn:Fe:LiNbO₃ crystals was characterized by the transmitted beam pattern distortion method. It increases remarkably when the concentration of ZnO is over a threshold concentration. Its value in Zn(7.0 mol%):Mn:Fe:LiNbO₃ crystal is about three orders of magnitude higher that in the Mn:Fe:LiNbO₃ crystal. The dependence of the defects on the optical damage resistance was discussed. The non‐volatile holographic storage was realized in all crystals, and the sensitivity of the Zn(7.0 mol%):Mn:Fe:LiNbO₃ crystal is much higher than that of others. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

KTP crystal growth from the starting materials reacted in solution

Using the solution‐reacted materials, potassium titanyl phosphate (KTiOPO₄, KTP) crystal was grown by the top‐seeded solution growth (TSSG) method. The solution‐reacted precursor was characterized by scanning electron microscope, and the solubility of KTP in K₈P₆O₁₉ was measured. The crystals were investigated by synchrotron radiation X‐ray topography, scattering centers measurement, weak absorption test and damage threshold test. The results showed that dispersion was better and solubility was higher than those by solid‐reacted method. Compared with the conventional crystal, KTP crystal grown from the solution‐reacted precursor had fewer defects, fewer scattering centers, lower weak absorption and higher damage threshold.     

Crystal growth of mixed‐valence ammonium vanadates

A new method has been developed for the synthesis of mixed‐valence ammonium vanadate crystals. Single crystals of (NH₄)₂V₃O₈ were synthesized on a large scale by hydrothermal reduction of NH₄VO₃ in ethanol‐H₂O solutions in the presence of triblock copolymer Pluronic P123. The crystals are shining thin plates with (001) cleavage planes. Calcination of the (NH₄)₂V₃O₈ crystals at 300°C or above resulted in pure phases of V₂O₅. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of large La1‐xPbxMnO3+δ (x=0.32–0.35) crystals

Large crystals of La_0.63Pb_0.37Mn O_3+δ with small La(Pb)‐ deficiency of about 0.005‐0.01 at.% were grown by high temperature solution growth method. The structure of the grown crystals was determined as rhombohedral with R‐3 space group by single‐crystal X‐ray diffractometry. The surface morphology of the crystals and the exact chemical composition was examined by scanning electron microscopy and energy dispersive X‐ray analysis methods, respectively. The IR‐transmission spectrum reveals the presence of Mn³⁺O₆‐ and Mn⁴⁺O₆‐ octahedra in the lattice of La_0.63Pb_0.37Mn O_3+δ crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Novel Nonlinear Optical Complex Crystal with an Organic Ligand Coordinated through an O Atom: Tetrathiocyanatocadmiummercury‐Dimethyl Sulfoxide

A novel nonlinear optical complex crystal with an organic ligand coordinated through an O atom: tetrathiocyanatocadmiummercury‐dimethyl sulfoxide, [CdHg(SCN)₄(H₆C₂OS)₂], (CMTD) is reported for the first time. Single crystals have been grown by temperature‐lowering method, the crystals tructure has been determined, and some physical properties are given. The relations between the crystal structure and nonlinear optical properties are also discussed.     

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)     

Temperature gradient controlled growth and optical properties of Er:BaY2F8 crystals

Single crystals of Erbium (Er) doped BaY₂F₈ have been obtained by the temperature gradient technique (TGT). No‐seed‐grown crystal of Er:BaY₂F₈, with the dimensions up to several centimeters, was obtained by self‐crystallization. The optimizations of various growth parameters were systemically investigated. The results indicated that the temperature gradient of 6‐7 K/mm and the cooling velocity less than 6 K/h were suitable for the crystal growth. The XRD data and the investigations on the growth striations by a stereo polarization microscope displayed that the [001] direction is the dominating direction for the crystal growth. The crystal grown by TGT often cracks along with the (100) plane, which is caused by the excessive decrease of the temperature during the crystal growth, for there is a rapid change in the thermal expansion curve of the BaY₂F₈ crystal in the temperature range from 800 °C to 900 °C. The spectral properties of Er:BaY₂F₈ single crystals have been studied and the effects of frequency up‐conversion of the crystals are reported. Spectral data suggest that the quality of Er:BaY₂F₈ crystal obtained by TGT method is good and the crystal has the potential application in laser devices. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study on rapid growth of KH2PO4 and its characterization

Large size crystals of KH₂PO₄ (KDP) were grown by adopting rapid growth technique from point seeds in a 1500‐liter crystallizer which is used to grow KDP crystals by conventional method. The grown KDP crystal size can reach to 310 × 310 × 320 mm³ and the average growth rate was 8mm/day. The optic properties of the rapidly grown KDP crystals were characterized comparing with the KDP crystals grown by the traditional temperature reduction method. We found it that the optical quality of the KDP crystals we grown rapidly are not significantly different from those of KDP crystals grown by traditional method. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fluorescence Lifetimes and Site-selective Photochemistry of Anthracene Crystals Doped with 2-hydroxyanthracene

The rise and decay of the prompt fluorescence of 2-hydroxyanthracene (2-OHA) doped anthracene crystals have been investigated at 8 K following excitation with frequency-doubled pico-second pulses from a synchronously pumped dye laser. By studying fresh crystals and crystals irradiated with u-v light at 298 K so as to introduce the photodimer, the roles played by the two different sites (O₈) and (O₉) occupied by the 2-OHA, by the X-traps and by other structural defects in fluorescence and energy transfer have been elucidated. Energy transfer between impurity sites (O₈ and O₉) is slow whereas that between guest associated X-traps and impurity is rapid. For the O₉ site, both before and after photodimerization, a simple time-independent energy transfer occurs from the anthracene host to the 2-OHA guest. The transfer to O₈ sites is associated with the presence of an extended region of disorder associated with the impurity. Such regions are excited directly.     

Growth of Eu(OH)3 large single crystals by solid KOH assisted hydrothermal method and luminescent and magnetic properties

Large single crystals of lanthanide hydroxides [Ln(OH)₃ (Ln = La, Pr, Nd, Sm, Eu and Tb)] up to several millimeters have been grown by using solid KOH assisted hydrothermal method. Eu(OH)₃ samples, as a representative of the Ln(OH)₃ crystals, were characterized by X‐ray diffraction (XRD), 4‐circle single‐crystal diffraction, Fourier transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS). FESEM image shows hexagonal prism morphology for the Eu(OH)₃ large crystals. Research on the photoluminescence and magnetic properties of Eu(OH)₃ species was conducted.