Growth,Structure And Nonlinear Properties Of Lead Oxyhalide Crystals

IR nonlinear optical?NLO?crystals materials played a key role in such optical fields as laser frequency conversion.The rapid development of lasers requires the higher performance and quality for nonlinear crystals.lead oxyhalide crystals are promising IR NLO materials,Due to the electronegative halide anion and the stereoactivity of the 6s² lone electron pairs of the Pb²⁺cations,the band gap and second-order nonlinear optical effects of lead oxyhalide crystals are much higher than those of existing commercial applications.Pb₁₇O₈Cl₁₈?POC?is a kind of great potential IR NLO material in recent years.However,it has not been widely used because of the difficulty in crystal growth.this paper explored the PbO-PbBr₂-PbCl₂ system to synthesized a new type of lead oxyhalide compound with NLO properties.The research work is carried out from raw material synthesis,crystal growth and NLO performance characterization,and the main contents are as follows:The Pb₁₇O₈Br₁₈?POB?and Pb₁₇O₈(Cl_1-xBr _x)₁₈?x=0.1-0.9??POBC?polycrystalline raw materials in the system were synthesized by secondary solid phase sintering.The thermal stability and crystallization behavior of the compounds were studied.Crystals were grown by micro pulling down method,the Bridgeman method and the solid phase method;Because of the severe volatilization of components,only tiny crystal particles could be obtained by micro pulling down method;By means of crucible selection,temperature field optimization and rate control,several centimeter crystals were successfully obtained by using the Bridgeman method:Pb₄?SiO₄?Br₄ crystals were obtained from quartz crucibles,and several crystals Pb₃O₂Br₂ were obtained from alumina crucibles,Pb₉O₄Br₁₀ crystals were grown by changing the ratio of raw materials.POB and POBC were also obtained by solid phase method,tiny crystal particles can be observed under an optical microscope.Through the refinement of the Rietveld structure of POBC,the crystal structure of POBC series compounds is obtained:orthorhombic system,the space group is Fmm2,no center of symmetry,and the lattice constants become larger as the concentration of Br increases.Fourier infrared,Raman,diffuse and second-order optical effects of the Pb₁₇O₈(Cl_1-xBr _x)₁₈?x=0-1?series of compounds were measured.The vibration and structure of the reaction from Fourier infrared and Raman spectroscopy are consistent with the structure.With the increase of Br,the infrared cut-off side length is gradually broadened,the band gap is gradually reduced but higher than AgGaS₂.The powder second-harmonic generation?SHG?measurement of Pb₁₇O₈(Br_0.5Cl_0.5)₁₈ showed that its nonlinear optical efficiency is 7 times larger than that of KH₂PO₄?KDP?,the curve of SHG intensity versus particle size at 1064 nm indicates phase-matching behavior.This paper provides important experience and reference value for the lead oxyhalide crystals growth,which is of great significance for exploring new nonlinear crystals.