Nonstoichiometry of the New Laser Host LiCaAlF6

LiCAF (LiCaAlF₆) and LiSAF (LiSrAlF₆) single crystals were grown by the Czochralski technique. DTA measurements of the grown crystals and of different mixtures within the ternary systems LiF—Me^IIF₂—AlF₃ (Me^II = Ca, Sr) lead to the conclusion, that LiCAF melts incongruently with a deficiency of CaF₂. For LiSAF congruent melting and no deviation from the ideal stoichiometry could be observed. From DTA results the enthalpies of fusion were determined: ΔH_LiCAF ≈︂ 110 kJ/mol, ΔH_LiSAF ≈︂ 80 kJ/mol. The circumstance, that LiSAF crystals are usually reported to have much better optical properties in comparison to LiCAF is attributed to these differences in the thermodynamic behaviour.     

Growth of NaBi(WO4)2 crystal by modified-Bridgman method

NaBi(WO₄)₂ (NBW) crystals have been grown for the first time by modified-Bridgman method. Influences of some factors on the crystal growth process are discussed. X-ray powder diffraction experiments show that the unit cell parameters of NBW crystal are a=b=0.5284 nm, c=1.1517 nm, and V=0.3215 nm³. The differential thermal analysis shows that the NBW crystal melts at 923°C.     

Crystal growth of NdAl3(BO3)4 from K2O/MoO3/Nd2O3/B2O3/KF flux

NdAl₃(BO₃)₄ single crystals were grown by the flux method and the TSSG technique using a K₂O/3MoO₃/B₂O₃/0.5Nd₂O₃/KF flux system. Light-violet clear crystals could be obtained. The effects of fluoride on the growth of NAB crystals were investigated. As the content of KF was gradually increased, the growth form of NAB was changed from the equant to the columnar and the primary crystalline region of NAB was shrinked. At the ratio of KF/K₂O = 0.75, NAB crystals could not be grown.     

Viscosity and IR investigations in the Li2O---B2O3 system

The high viscosity in melts of the Li₂O---B₂O₃ system makes it very difficult to grow large crystals of lithium triborate. The viscosity and IR characteristics of molten li₂O---B₂O₃ system are reported in this paper. When the temperature increases the viscosity of li₂O---B₂O₃ system decreases and follows an Arrhenius-type relationship. With an increasing 13203 ratio in Li₂O---B₂O₃ melts, the viscosity rises gradually to a maximum with a composition Li₂O: 3.513203 then it falls rapidly. In order to find active agents to reduce the viscosity, Na₂O, NaCl, LiF, P205, M003, W03 etc oxides were added to Li₂O---B₂O₃ samples respectively and investigated using the orthogonal method. The experimental results show that the addition of acidic oxides can significantly decrease the viscosity in the Li₂O---B₂O₃ system. For Li₂O: 4.513203, an ideal additive agent is 20wt% Li₂O:: 2MoO₃. Near the composition for crystal growth, the percentage reduction of viscosity is 62.2%. The IR spectra of Li₂O---B₂O₃ system revealed that the BO₄⁻/NO₃⁻ ratio is reduced in the melt using Li₂O: 2MoO₃ as an additive. It is proposed that the M003 reduced the concentration of bridging oxygen atoms of BO₄⁻. The change of structure explains the decline in the viscosity. In the crystal structures of lithium triborate, the matrix spaces are so small that larger other cations than Li+ are very difficult to enter the crystal matrix. So the use of additive agents to reduce the viscosity is a possible method if no new phase appears.     

Ternary Colquiriite Type Fluorides as Laser Hosts

The Cr³⁺:LiCaAlF₆ (Cr:LiCAF) and Cr³⁺:LiSrAlF₆ (Cr:LiSAF) laser host crystals can be grown by the Czochralski technique. Problems result from the evaporation of lithium-aluminium-fluorides during the growth process and a corresponding stoichiometry shift of the melt towards the CaF₂ (SrF₂) corner of the ternary concentration triangle. Both Cr:LiCAF, and to a lower extend also Cr:LiSAF, contain micron-sized defects that disturb the lasing efficiency heavily. The defects are assumed to be related to water and/or oxygen impurities within the starting materials and growth atmosphere and to peculiarities of the LiF – CaF₂ – AlF₃ ternary phase diagram.     

Growth and properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals directly from melt

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by a modified Bridgman method directly from melt using an allomeric Pb[(Mg_1/3Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal as a seed. X-ray diffraction (XRD) measurement confirmed that the as-grown PZNT91/9 single crystals are of pure perovskite structure. Electrical properties and thermal stabilization of PZNT91/9 crystals grown directly from melt exhibit different characters from those of PZNT91/9 crystals grown from flux, although segregation and the variation of chemical composition are not seriously confirmed by X-ray fluorescence analysis (XPS). The [0 0 1]-oriented PZNT91/9 crystals cut from the middle part of the as-grown crystal boules exhibit broad dielectric-response peaks at around 105 °C, accompanied by apparent frequency dispersion. The values of piezoelectric constant d₃₃, remnant polarization P_r, and induced strain are about 1800–2200 pC/N, 38.8 μC/cm², and 0.3%, respectively, indicating that the quality of PZNT crystals grown directly from melt can be comparable to those of PZNT91/9 single crystals grown from flux. However, further work deserves attention to improve the dielectric properties of PZNT crystals grown directly from melt. Such unusual characterizations of dielectric properties of PZNT crystals grown directly from melt are considered as correlating with defects, microinhomogeneities, and polar regions.     

Thermal and laser properties of Yb:YAl3(BO3)4 crystal

Large optical-quality Yb:YAl₃(BO₃)₄(Yb:YAB) crystals have been grown by the flux method. The thermal properties of Yb:YAB crystal were measured for the first time. The thermal properties of Yb:YAB crystal with different Yb³⁺ ion concentrations are also reported. The results show that the ytterbium concentration influences the properties of Yb:YAB crystal. The specific heat decreases with the increase of Yb³⁺ ion concentrations in the experiment range. Apparently, the thermal expansion coefficient increases along the c-direction with the increase of Yb³⁺ ion concentrations, while it changes slightly along the a-direction. The output laser in 1120–1140 nm ranges has been demonstrated pumped by InGaAs laser. The slope efficiency is 3.8%. The self-frequency-doubling output power of 1 mW is achieved.     

Crystal growth and optical characterization of Cr,Ca: Y3Al5O12

Single crystals of Cr,Ca: Y₃Al₅O₁₂(YAG) with different Cr and Ca concentrations were grown by the Czochralski (CZ) and floating zone (FZ) method. The analysis of absorption and emission spectra of both as-grown and oxygen-annealed crystals in relation to concentration ratio of Ca and Cr (Ca/Cr) showed that Cr⁴⁺ concentration ratio to total Cr concentration increased up to about Ca/Cr = 6, and Cr⁶⁺ can also exist. Luminescence lifetime at 1400 nm was measured as a function of Cr⁴⁺ concentration.     

Czochralski grown Ga2O3 crystals

We report on the successful growth of β-Ga₂O₃ single crystals using the Czochralski method. Model calculations show that the gas phase consists of Ga₂O, GaO or Ga independent of the ratio of oxygen and Ar or N₂. We find that for growing single crystals the evaporation has to be suppressed by a finite amount of oxygen. A CO₂/Ar gas atmosphere was found to meet this requirement.     

Cr:LiSrAlF_6 晶体生长及其性能表征(英文)

本文报道了布里奇曼法生长的高品质Cr:LiSrAlF6晶体及其激光特性。采用固相氟化反应除去原料中的氧化物和水。在较小的温度梯度和较慢的生长速率下生长出的Cr:LiSrAlF6晶体尺寸达到2 0mm× 130mm。均匀的Cr3 +掺杂浓度为 1～ 15mol%。从XRD谱图计算出的Cr:LiSAF晶体点阵参数为a =0 .5 0 2nm ,c =0 .96 7nm。测试了晶体的吸收曲线 ,并分析了其吸收与能带结构的关系。实现了闪光灯泵浦的Cr:LiSAF激光器运转 ,激光转换斜效率达到 5 .85 %。     

Top-seeded solution growth of LiB3O5

We report on the top-seeded solution growth of LiB₃O₅ from an excess B₂O₃ solution. Parameters investigated include the Li₂O/B₂O₃ ratio, rotation rate, pulling rate, cooling rate, and seed direction. With careful control of the above parameters, we have grown clear crystals of 25 × 30 × 20 mm in size. Selected nonlinear optical properties of these crystals are reported. Observations concerning the occurrence of unstable growth (inclusions, hopper growth) are discussed, and methods to eliminate the unstable growth are suggested.     

Two-level growth of potassium niobate KNbO3 single crystals: a new growth method for ABO3-type materials

Based on our recent study on the directional growth of KNbO₃ single crystals, a new growth scheme called the two-level growth (TLG) has been developed. By using the TLG method, high quality transparent KNbO₃ single crystals can be prepared with high reproducibility. The technique includes two growth stages. In level-one growth, a dimensionally defined (shaped) KNbO₃ seed with high crystal perfection is fabricated. The target crystal with desired dimensions and an architectural structure can be obtained in the second level of the growth. A process flow chart for the TLG method has been presented and six representative types of the growths have been introduced. Generally, crystals grown by TLG have much less crystal imperfections than those obtained from the conventional way. Technological merits of the TLG scheme have been studied, indicating that this growth scheme can also be employed to other oxide perovskite ABO₃ single crystal growths.     

Characteristic crystal growth from amorphous WO3 film by vacuum heating

Selective growth of WO₂, W and WO_3−x crystals from amorphous WO₃ film by vacuum heating at 400–900°C was clarified. The grown WO_3−x crystals were incommensurate structure based on crystallographic share structure. The growth process of WO₂ crystal in the amorphous film was directly observed at high temperature in the electron microscope. The growth front of the WO₂ crystal consumes WO₃ microcrystallites with various orientations. The growth speed of the WO₂ depended on WO₃ microcrystallites orientation. The origin of the wavy growth front of WO₂ was due to an orientation dependence of the WO₃ microcrystallites.     

Phase diagram of the SrS–Ga2S3 system and its application to the single-crystal growth of SrGa2S4

Ce-doped SrGa₂S₄ compound is expected as a new host material of blue EL devices. However, the basic properties of bulk single crystals have not been fully clarified, since this compound has been mostly synthesized in the form of polycrystals or thin films. Here, we firstly present the pseudo-binary phase diagram of the SrS–Ga₂S₃ system constructed in accordance with our DTA data for single-crystal growth of SrGa₂S₄. It is shown that SrGa₂S₄ compound has a congruent melting point and a eutectic reaction in the side of excess of Ga₂S₃ concentration. On the basis of the phase diagram, single crystals of SrGa₂S₄ are grown using Ga₂S₃ as a self-flux in a horizontal Bridgman furnace. Colorless and transparent crystals having a typical size 2×2×2 mm³ are obtained.     

A glass-forming system with compound-forming tendency: As4S6---P4S10

Glasses in the quasi-binary system (As₄S₆)_x(P₄S₁₀)_1−x x = 0.1, …, 1.0, are produced and studied by thermal analysis, X-ray, and Raman spectroscopy. The phase diagram of the system and the critical cooling rate for glass formation both have their maximum at x = 0.5, corresponding to the compound As₂P₂S₈; the X-ray structure of recrystallized samples can be described as a sum of the As₂P₂S₈ (x = 0.5)- and the P₄S₁₀-structure (As₄S₆ not visible); Raman spectra of the glasses are again sums of As₂P₂S₈- and As₄S₆/P₄S₁₀-spectra. All these observations support the assumption that a stable building block corresponding to the 1:1 compound As₂P₂S₈ and surplus As₄S₆ (or P₄₁₀) are the essential elements of the structure in the glasses.     

Flux growth of BPO4 crystals

Single crystals of BPO₄ with sizes up to 15×10×12 mm³ were grown by top-seeded solution growth method using Li₂O–Li₄P₂O₇ as fluxes. The components volatilized from the melt were characterized by the method of X-ray powder diffraction. The defects of grown crystals have also been investigated. The measured ultraviolet cutoff edge of BPO₄ was about 130 nm. Its density was 2.82 g/cm³ determined using drainage method.     

Growth and luminescence mechanisms of Ba2ErCl7: a new laser up-conversion crystal

A modified synthesis method for the preparation of Ba₂ErCl₇, a new laser up-conversion material using Er₂O₃, BaCl₂·2H₂O and NH₄Cl, is reported for the first time. Single crystals 5–8 mm in diameter and 10–20 mm in length were grown by both the Czochralski and Bridgman methods. The transmittance spectra for a Ba₂ErCl₇ single crystal was first measured using a HITACHI U-3500 spectrophotometer. There were three intense absorption peaks ⁴I_9/2, ⁴I_11/2 and ⁴I_13/2 in the infrared range which can be excited by 803 and 980 nm and 1.5 μm laser diode (LD), respectively. The cut-off wavelength of the crystal was 230 nm. Intense green luminescence was observed when the crystals were pumped by an 803 nm LD. Up-conversion mechanisms are discussed.     

Mössbauer studies on some glasses and crystals in the Na2O---Fe2O3---SiO2 system

Mössbauer absorption measurements have been made at room temperature on ⁵⁷Fe in iron sodium silicate glasses containing 3–15 mol% Fe₂O₃ and various iron alkali silicate crystals in order to study the state of iron in these glasses. The spectra of all the glasses gave one doublet with a quadrupole splitting varying from 0.73–0.78 mm s⁻¹, while those of Na₂O · Fe₂O₃ · 4 SiO₂ and 5 Na₂O · Fe₂O₃ · 8 SiO₂ crystals showed much smaller quadrupole splitting, 0.28 mm s⁻¹ and 0.10 mm s⁻¹, respectively, and an asymmetrical doublet of much narrower linewidth. When sodium was replaced by other alkali metals of larger size, such as K and Cs, in MFeSi₂O₆ and MFeSi₃O₈ crystals, the quadrupole splitting became wider and approached to 0.73 mm s⁻¹. Such a variation was not observed for glasses. These results suggest that a larger number of non-identical sites exist in iron sodium silicate glasses than in the corresponding crystals.     

Study on phase diagram of Bi2O3---SiO2 system for Bridgman growth of Bi4Si3O12 single crystal

Phase relation of Bi₂O₃---SiO₂ system was evaluated experimentally from DTA and XRD measurements and its stable and metastable phase diagrams were proposed. Although BSO melts near-congruently at 1025°C in the stable phase equilibrium, its melt crystallizes to form metastable phase Bi₂SiO₅ in accordance with the metastable phase diagram while cooling. Therefore, BSO couldn't nucleate and crystallize spontaneously without crystal seed and only Bi₂SiO₅ crystallized at about 850°C with significant supercooling during Bridgman growth. BSO single crystal with 20×20×100mm³ was grown in a vertical Bridgman furnace with a BSO seed according to its phase diagram. The measuring results of scintillation properties of BSO specimen show that its decay constant is 91 ns (about 1/3 of BGO) and light output is 23% of BGO.     

Flux growth of PbMg1/3Ta2/3O3 single crystals

Single crystals of PbMg_1/3Ta_2/3O₃ (PMT) were grown by the flux method. The PbO–Pb₃O₄–B₂O₃ system was used as a solvent. Transparent and light yellow PMT single crystals of rectangular shape and dimensions up to 10×6×4 mm³ were obtained. For the applied growth conditions only, the crystals of the perovskite structure were grown. X-ray diffraction tests showed that at room temperature PMT exhibits cubic symmetry with lattice parameter a=4.042(1) Å. Dielectric studies pointed to relaxor properties of PMT. The characteristic broad and frequency-dependent maximum of dielectric permittivity was observed at 179.7 K (1 kHz).