Research On The Synthesis, Growth And Properties Of New Ultraviolet And Deep-ultraviolet Nonlinear Optical Crystal Materials

In this dissertation, ultraviolet and deep-ultraviolet NLO crystals such as NaBa₄Al₂B₈O₁₈Cl₃, BPO₄ and BaAl₂B₂O₇ were studied. The major work consisted of solid-state synthesis, flux search, crystal growth, crystal structure determination and measurement of crystal properties, etc. The main work and results are as follows:1. Polycrystalline NaBa₄Al₂B₈O₁₈Cl₃ was synthesized at the molar ratio of Na:Ba:Al:B:O:Cl=1:4:2:8:18:3 with raw materials by the high temperature solid state reaction at about 800℃. Through lots of experiments of searching for flux, we found NaF, LiCl or mixture of them could be used as flux to grow NaBa₄Al₂B₈O₁₈Cl₃ crystals. With the ratio of solute to solvent ranging from 5:1 to 3:1, the transparent crystals, the maximum size up to 34mm×34mm×16mm, were obtained. The elements of the crystal grown from mixture of NaF and LiCl flux were measured with ICP-OES and ICS. The results showed F- ions were incorporated into the crystal and Cl- ions were reduced correspondingly.2. The crystal structure of NaBa₄Al₂B₈O₁₈Cl₃ was determined by the single crystal X-ray diffraction method. It belongs to tetragonal crystal system with space group P42nm and cell parameters:a = 12.0480 (16) ?,c = 6.8165 (11) ?, V= 989.4(3)?3,Z=2. The cell lattice contains BO₄, BO₃ and AlO₄ groups. Two BO₃, two BO₄ and one AlO₄ make up of [AlB₄O₁₂]₉- group and [AlB₄O₁₂]₉- groups link one another by sharing O atom. In this way, it forms a three-dimensional network containing channels which run parallel to a, b and c respectively. Ba²⁺,Cl- and F- ions located at the channels.3. The crystal properties, such as powder second-harmonic generation effect, transmission spectrum, infrared spectra, refractive indices, thermal properties, conoscope interference patterns , hardness, deflect, density and physical or chemical stabilization were studied. NaBa₄Al₂B₈O₁₈Cl₃ crystal was found to have a smaller powder SHG efficiency compared with that of KDP. The transmission spectrum of the crystal showed the UV cutoff edge is at 230 nm, The infrared spectra confirmed there exist BO₄,BO₃ groups. The refractive indices of the crystal were measured by the minimum deviation technique, and the Sellmeier equation was given as follow: The differential thermal analysis curves of the NaBa₄Al₂B₈O₁₈Cl₃ crystal grown from LiCl flux and the polycrystalline synthesized by solid state reaction show a sharp endothermal peak at about 964℃.The measured density of the crystal is 3.655 g per cm³ by the buoyant density method. Its Mohs hardness is about 5.6⁵.7. The conoscope interference patterns of (001) face show it is a uniaxial crystal. Inclusions, growth striations and scatter particles could be observed in the crystals. The etched pits on the (100) face exhibit rectangular which are parallel to c direction. The NaBa₄Al₂B₈O₁₈Cl₃ crystal exhibits a good machining property and it is stable in atmosphere and free of moisture, but easy to dissolve in acid.4. Polycrystalline BPO₄ was synthesized by solid state reaction. The growth of BPO₄ crystal with Li₄P₂O₇-Li2O, Li₄P₂O₇-NaCl and Li₄P₂O₇-NaF as flux was studied. New flux, i.e. Li₂O-MoO₃ was found to be suitable for growth of BPO₄ crystal. Better quality BPO₄ crystals were obtained with Li₂O-MoO₃ flux. The ideal morphology of BPO₄ crystal was described. The hardness of BPO₄ crystal was measured and its Mohs hardness on (101) face is about 5.77.5. Polycrystalline materials was synthesized at the molar ratio of Ba:Al:B:O=1:2:2:7 by solid state reaction. The powder diffraction patterns of the polycrystalline differ from that of BABO reported by as-known papers. Differential thermal analysis, measurements of infrared spectra, elements and powder second-harmonic generation effect were performed on the polycrystalline materials. It is estimated a new phase of BABO. The differential thermal analysis curve of the polycrystalline show a sharp endothermal peak at 973℃. The infrared spectrum indicated there exist BO₃ groups in the crystal. The powder SHG effect of the polycrystalline is as about 1 to 2 times as that of KDP (KH₂PO₄). Through lots of experiments of searching for flux, we found PbF₂-H₃BO₃, NaF and some based-on NaF fluxes could be used to crystallize BABO crystals. When NaF was used, the suitable ratio of BABO to NaF ranged from 10:1.0 to 10:1.5. However, all these fluxes aren't appropriate to grow BABO crystal because of the high viscosity, volatility of the melt which lead to deviation of the component or fluctuation of crystallization temperature. Up to today, it is difficult to grow better quality or larger size BABO crystal.