Research On Some New Borate Nonlinear Optical Crystal Materials

In this dissertation, the synthesis, growth and properties of new ultraviolet nonlinear optical crystal materials, which consist of CsB3O5 crystals, Ca5(BO3)3F crystals and new borate compounds, have been studied. The main works are as follows:1. Flux growth of CsB3O5 crystalsIn this study, CsB3O5 crystals have been grown successfully using two types of fluxes, viz. alkali-metal fluorides and alkali-metal oxides. In alkali-metal fluorides, the phase diagrams of CsB3O5-LiF and CsB3O5-NaF, systems were investigated, and the regions for growth of CBO crystals were determined. In CsB3O5-LiF system, CBO crystals can be grown from 0 to 42mol%LiF, and the temperature is between 825 and 709℃; In CsB3O5-NaF, CBO crystals can be grown from 0 to 40mol%NaF, and the temperature is between 825 and 690.5℃. The volatility of the two systems was measured and the proper ratios of two fluxes were determined by growth experiments.In alkali-metal oxides, the regions for growth of CBO crystals were determined in the Li2O-Cs2O-B2O3 and Na2O-Cs2O-B2O3 systems. The transparent CBO crystals can be grown by the proper ratios of the two fluxes.The observation of light scattering centers was carried by 150-mW diode pump laser beam. The results showed that there were some light scattering centers in CBO crystals grown from LiF and NaF fluxes, and no light scattering centers in CBO crystals grown from the proper ratios of Li2O and Na2O fluxes. The light scattering centers were mainly nano-scale inclusions in CBO crystals grown from fluxes.2. Research on Ca5(BO3)3F crystalsIn this study, we reported on the synthesis of Ca5(BO3)3F compound by solid-state reaction at the temperature of 1000℃. Differential thermal analysis (DTA) showed that Ca5(BO3)3F melts incongruently, the crystal growth of Ca5(BO3)3F was needed by flux method in our lab conditions. We found three fluxes viz. LiF, LiF-B2O3-CaO system and LiF-CaMoO4 system, to grow this crystal. Powder second-harmonic generation (SHG) test showed that Ca5(BO3)3F could be phase-matchable, and SHG effect of Ca5(BO3)3F was about 2 times as large as deff of KDP. Transmission spectrum showed that the UV cutoff for Ca5(BO3)3F crystal was about 190nm. Ca5(BO3)3F has potential application as a nonlinear optical material in UV region.3. Investigation of new borate materialsThrough the investigation of Cs2O-BaO-B2O3 system, we found a new ternary borate oxide, CsBaB3O6. It has been synthesized by solid-state reaction at 700℃, and the single crystals were grown using CsF as a flux. It crystallizes in the hexagonal space group P321 with a cell of dimensions a= 12.469(3)?, c=7.444(3)?,α=90.00°,γ=120.00°, V = 1002.3(5)?3, Z =6. No second harmonic signal was detected in our SHG test, and the UV cutoff wavelength is about 190 nm. Besides that, we have investigated the Rb2O-BaO-B2O3 system, and found a new compound Rb-Ba-B-O, whose structure is being solved.Another interest was focused on alkaline-metal mixed borates. Sr2MgB2O6 has been synthesized by solid-state reaction at 950℃. The DTA shows that the melting point of Sr2MgB2O6 is above 1250℃, and single crystals of Sr2Mg(BO3)2 have been obtained using SrF2-LiF as a flux. It crystallizes in the monoclinic system (space group C2/m), with a cell of dimensions a a= 9.038(9)?,α=90.00°, b=5.150(6)?,β=118.72(6)°, c=6.106(6)?,γ=120.00°, V = 249.2(4)? 3,Z = 2. The transmission spectrum of Sr2Mg(BO3)2 crystals shows the cutoff wavelength is below 185 nm.The other interest was focused on investigation of BaO-Na2O-B2O3-NaF system, we found a new fluoroborate, Na3Ba2B6O12F. It has been synthesized by solid-state reaction at 700℃, and it melts congruently, the single crystals were grown from melt. It crystallizes in the hexagonal space group P63/m with a cell of dimensions a = 7.3471(3)?,b = 7.3471(3) ?,c = 12.6052(5) ?,α=90.00°,γ= 120°, V=589.27(4) ? 3,Z=2.