[en] The reactivity of viscous melts has been analyzed as a function of the degree of anion polymerization. Precise techniques are proposed for detecting the phase relations and kinetics of high-temperature crystallization of new materials in four-to-six-component borate and tantalate systems. For rare earth polyfunctional borates RAl₃(BO₃)₄ (R = Y or lanthanides), efficient frequency conversion with parameters greatly exceeding the corresponding parameters for known media has been demonstrated for the first time. The conditions for fabrication of refractory optical single crystals having high thermal conductivity and other record characteristics (in comparison with the known diode-pumped lasers) for femtosecond integrated optics have been optimized. Bases of the laboratory technology of growth of such crystals are considered.

[en] We have found conditions for reproducible spontaneous crystal growth of (R_xLa_{1 –x})Al_2.07(B₄O₁₀)O_0.6 (R = Ce, Pr; x = 0, 0.003, 0.03, 0.5, 1) dimetaborate solid solutions. The composition and morphology of the crystals have been studied and limitations on isomorphous substitutions on the rare-earth site within the stability range of their structure type have been found out. We have studied the thermal properties of lanthanum dimetaborate. According to differential thermal analysis, X-ray diffraction, and analytical scanning electron microscopy data, this compound melts incongruently in the range 1120–1200°C, with a maximum endothermic peak at 1165°C. The decomposition products have been shown to include Al₁₈B₄O₃₃, Al₄B₂O₉, and LaBO₃.

[en] A correlation has been revealed between the formation conditions, composition, morphology, and physicochemical properties of NaBi_1-x(W_1+yO₄)₂ crystals (0 ≤ x ≤ 0.16, 0 ≤ y ≤ 0.11). The effect of melt deviation from stoichiometry on the decomposition rate of grown crystals under electron beam irradiation is shown by transmission electron microscopy. A nonuniform dopant distribution over the crystal boule cross-section is found by microprobe analysis. The Raman spectra of the samples depend on their crystallographic orientation.

[en] The phase relationships in the YbAl₃(BO₃)₄-K₂Mo₃O₁₀-B₂O₃-Yb₂O₃ multicomponent system are investigated in the temperature range 1150-1000 deg. C within the stability region of the YbAl₃(BO₃)₄ compound. The region of single-phase crystallization of the YbAl₃(BO₃)₄ borate is revealed in the section corresponding to the composition containing 15 wt % YbAl₃(BO₃)₄. For the same composition, it is demonstrated that there exists a correlation between the temperatures of saturation of melt solutions with the YbAl₃(BO₃)₄ borate and the composition of the solvent, namely, the contents of B₂O₃, K₂Mo₃O₁₀, and Yb₂O₃ in the solvent. The temperature dependences of the solubility of the YbAl₃(BO₃)₄ compound at different contents are determined for melts of two compositions: melt I containing 55 mol % K₂Mo₃O₁₀ and 45 mol % B₂O₃ and melt II containing 55 mol % K₂Mo₃O₁₀, 40 mol % B₂O₃, and 5 mol % Yb₂O₃. The specific features of the crystallization of the YbAl₃(BO₃)₄ compound are analyzed and compared with those of the yttrium, neodymium, gadolinium, and erbium aluminum borates studied previously

[en] (Er,Yb):YAl₃(BO₃)₄ single crystals of optical quality, up to 15 × 10 × 10 mm³ in size, have been grown from a (Er_0.023Yb_0.116Y_0.862)Al₃(BO₃)₄ solution in a Y₂O₃-B₂O₃-K₂Mo₃O₁₀ melt. The initial borate concentration was 17 wt %, and the flux cooling rate increased from 0.08 to 0.12°C/h in the range 1060–1000°C. The physical properties of the single crystals grown are good enough that they can be used as laser elements in systems with diode pumping and radiation near 1.5 μm.

[en] (Er,Yb):YAl₃(BO₃)₄ single crystals of optical quality, up to 15 x 10 x 10 mm³ in size, have been grown from a (Er_0.023Yb_0.116Y_0.862)Al₃(BO₃)₄ solution in a Y₂O₃-B₂O₃-K₂Mo₃O₁₀ melt. The initial borate concentration was 17 wt %, and the flux cooling rate increased from 0.08 to 0.12 deg. C/h in the range 1060-1000 deg. C. The physical properties of the single crystals grown are good enough that they can be used as laser elements in systems with diode pumping and radiation near 1.5 μm

[en] 

Abstract

: We have studied and optimized conditions for spontaneous flux growth of RMgB₅O₁₀ (R = Y, La, Gd) crystals and assessed the feasibility of seeded growth of such crystals. Using high-temperature solution growth with K₂Mo₃O₁₀ as a solvent, we have prepared optical-quality (Er,Yb):YMgB₅O₁₀ single crystals and measured their thermal conductivity and optical characteristics to assess their potential for use in diode-pumped lasers operating in the spectral range 1.5–1.6 μm. Absorption cross section spectra of an (Er,Yb):YMgB₅O₁₀ single crystal have been measured in the spectral ranges 800–1100 and 1400–1650 nm. The results demonstrate that (Er,Yb):YMgB₅O₁₀ single crystals are similar in characteristics to (Er,Yb):YAl₃(BO₃)₄, promising for use in advanced near-IR laser systems, and are capable of replacing RAl₃(BO₃)₄ materials in such devices because they are simpler to grow.

[en] We have studied phase relations in the pseudoquaternary system LuAl₃(BO₃)₄–(K₂Mo₃O₁₀–Al₂O₃–B₂O₃) in the temperature range 1130 to 900°C. The phase relations were represented in graphical form, as a projection of the formation of solid phases in this range onto the composition triangle at 900°C. Optimal results in terms of high-temperature solution growth have been obtained at 25 wt % LuAl₃(BO₃)₄ in the growth charge. Undoped and erbium–ytterbium codoped LuAl₃(BO₃)₄ (LuAB) single crystals have been grown from high-temperature solutions on “pointlike” seeds. The (Er,Yb):LuAB crystals are similar in thermal properties and luminescence spectra to (Er,Yb):YAl₃(BO₃)₄ and (Er,Yb):GdAl₃(BO₃)₄ crystals and can be used in diode-pumped lasers operating in the nominally eye-safe spectral region 1.5–1.6 μm.

[en] Luminescence spectra of single crystals of rare-earth gallium borates LnGa₃(BO₃)₄ (Ln = Nd, Sm, Tb, Er, Dy, or Ho) at room (300 K) and cryogenic (10 K) temperatures are presented for the first time. Photoluminescence has been recorded in the wavelength range of 470–5000 nm (2000–21 300 cm^–1) with a high spectral resolution (down to 0.1 cm^–1) upon excitation by different diode lasers. The spectra obtained cannot be unambiguously interpreted within one luminescent center, which can be due to the presence of defects and/or inclusions of other crystalline phases. The optical nonlinearity of rare-earth–gallium borates has been estimated using the Kurtz–Perry powder technique. The typical intensities of the second-harmonic generation in gallium borate powders are 30–40 (with respect to quartz), and the optical nonlinearity is as good as the nonlinearity of the efficient rare-earth aluminum borate YAl₃(BO₃)₄.

[en] This work is devoted to the investigation of GdCr_3(BO_3)_4 crystals by the method of infrared spectroscopy. Incongruently melting borate GdCr_3(BO_3)_4 was obtained as a result of spontaneous crystallization. Crystal structures were identified by the method of infrared spectroscopy. Ab initio calculations in the frame of density functional theory enabled us to separate modes belonging to the R32 and C2/c phases and to estimate the ratio of these phases in GdCr_3(BO_3)_4 crystals. We have found that the content of the rhombohedral R32 (non- centrosymmetric) modification is about 85%. (paper)