No abstract

Single crystals of LuAl3(BO3)4 (LuAB) have been grown with the top-seeded solution growth method from a new tungstate based flux Li2WO4–B2O3. The crystallization region of LuAB is revealed in a quasi-ternary system of LuAB–Li2WO4–B2O3. Correlation between the crystallization region of LuAB and an excess of Al2O3 in the flux system has been identified for the first time. Compared with the commonly used K2Mo3O10–B2O3 flux at 1100 °C, the Li2WO4–B2O3 flux has lower volatility with lower incorporation of tungstate into the crystals. Thermophysical properties of the crystal have been investigated for the first time, where the thermal expansion coefficients along two crystallographic directions in the temperature range of 30–800 °C were determined to be α1 = 3.38 × 10–6 K–1 and α3 = 10.4 × 10–6 K–1. The specific heat was about 0.65 J/(g·K) at room temperature. The thermal conductivities at room temperature were 12.47 W/(m·K) and 10.443 W/(m·K) along the a and c axes, respectively, and the Vickers hardness values were measured at 1449 (HV) for (100) and 1595 (HV) for (001) faces.

The optical properties of pure LuAl(3)(BO(3))(4) (abbreviated as LuAB) crystals were investigated for the first time. Large UV-transparent LuAl(3)(BO(3))(4) crystals were grown by a high-temperature top-seeding method with Li(2)WO(4)O(7)-B(2)O(3) as the flux. The refractive indices of LuAl(3)(BO(3))(4) at several wavelengths covering ultraviolet-visible and near-infrared regions were measured by the auto-collimation method. The parameters of Sellmeier's dispersion equation were determined from the experimental data. The phase-matching curve of second harmonic generation was measured. The nonlinear optical coefficient d(11) of LuAB crystal was determined to be 1.10 pm/V by a phase-matching method. The UV cut-off wavelength of the LuAl(3)(BO(3))(4) crystal was shorter than 190 nm.

Two ternary infrared nonlinear optical materials Cd4SiS6 (1) and Cd4SiSe6 (2) with polar space group Cc were obtained by mixing d10 configurations-central tetrahedra motifs and nonlinear optical (NLO)-active distorted MIVQ4 tetrahedra motifs in a non-alkaline earth metals-containing system. They exhibited an interesting three-dimensional (3D) framework structure, and millimeter-level single crystals were successfully grown by a chemical transport reaction. Comprehensive optical measurements indicated that they achieve coexistence of good second-harmonic generation (SHG) responses (1.3 and 1.9 × AgGaS2 at 74–106 μm particle size) and high laser-induced damage thresholds (8.6 and 7.1 × AgGaS2 at 1064 nm laser) and wide infrared (IR) transparent regions (0.45–17.6 μm for 1, 0.64–20.3 μm for 2). Furthermore, theoretical studies revealed that their SHG effects originate from two functional building motifs (FBMs) CdQ4 and SiQ4 tetrahedra, shedding light on the exploration of new IR NLO materials with mixed FBMs.