Growth And Properties Of Novel Nonlinear Optical Borate Crystals

Owing to expanding the frequency range of solid laser sources, the inorganic nonlinear optical (NLO) borate crystals have been widely used in optical communication, laser medicine and signal processing. Numerous investigations have been undertaken on new NLO crystals, which are characterized by a large NLO coefficient, a broad optical transparency range, a high damage threshold and high optical quality. In present dissertation, the aim is to find some new NLO borate crystals.Firstly, the growth and properties of Cd₃Zn₃B₄O₁₂ crystal have been studied in detail. Cd₃Zn₃B₄O₁₂ polycrystals were synthesized by solid-state and wet chemical reaction method successfully, and the latter is the more effective way to prepare single-phase compound. Cd₃Zn₃B₄O₁₂ single crystals have been grown by the flux method. Twenty-four fluxes and sixty samples have been used for the crystal growth. The experiment results show that Cd₃Zn₃B₄O₁₂ crystals with millimeter grade were grown from the self-flux B₂O₃ (Cd:Zn:B=1:1:1.5); and larger crystals were obtained from the PbO-0.85PbF2 fluxes easily. The grown crystals were characterized by Differential Scanning Calorimetry and Thermogravimetric (DSC/TG), Infrared and Raman analysis, NLO effect and chemical stability. The analytical results indicate that Cd₃Zn₃B₄O₁₂ crystal exhibits an excellent NLO effect, and is very stable in neutral solution and not hygroscopic in air at room temperature.Secondly, crystal growth in other different ratio compounds has been investigated in the CdO-ZnO-B₂O₃ system. The experimental results show that the wet chemical method is a better way than the solid-state reaction method to prepare pure cadmium dizinc diborate compound. The CdZn₂B₂O₆ single crystals have been grown by the Kyropoulos method and the vertical Bridgman method for the first time. The properties of the CdZn₂B₂O₆ are similar to these of Cd₃Zn₃B₄O₁₂, including the crystal structure, XRD, Infrared and Raman analysis. The Cd²⁺ and Zn²⁺ cations in the two compounds share the same site in the unit cell and the distribution is disordered, thus the occupancy positions differences of the Cd2+ or Zn2+ cations result in different ratios of Cd and Zn in the crystals. The Cd and Zn ratios of CdZn₂B₂O₆ and Cd₃Zn₃B₄O₁₂ crystals were assigned to be 1:2 and 1:1, based on the result of the Ionic Coupled Plasma Atom Emission Spectrometer (ICP-AES) analysis. The theoretic analysis and experimental results denote the existence of the two crystals, and provide a satisfying explanation on the similar properties. The powder NLO coefficient of the CdZn₂B₂O₆ crystal is 2.6 times as large as that of KH₂PO₄ (KDP) crystal, and this stable crystal is a promising material for NLO applications in ultraviolet-transparent range.Lastly, starting with the change of CdO or ZnO in the CdO-ZnO-B₂O₃ system, new NLO borate crystals have been researched using high-temperature solid-phase and wet chemical reactions, crystal growth and powder NLO effect methods. Over forty samples in nine systems have been studied, such as BaO-ZnO-B₂O₃, SrO-ZnO-B₂O₃, CaO-ZnO-B₂O₃, MgO-ZnO-B₂O₃, Yb₂O₃-ZnO-B₂O₃, La₂O₃-ZnO-B₂O₃, Gd2O3-ZnO-B₂O₃, CdO-SrO-B₂O₃ and so on. The growth and properties of Ba_2.80Zn_0.20B₆O₁₂ and CdZn₂KB₂O₆F new borate crystals have been investigated. The XRD and crystal structure of Ba₂ZnB₆O₁₂ crystal have been corrected, and the analysis of differential thermal, Infrared and Raman have been supplemented. At the same time, ZnO single crystal has been grown from the SrB₂O₄, Bi4B2O9, CdB2O4 and BaB₂O₄ fluxes respectively.In addition, the etching patterns on different surfaces of CsLiB₆O₁₀ (CLBO) crystal and its cracking mechanism have been investigated. The cracking evolution of CLBO crystal immerged in pure water was exhibited and discussed finally.