Exploration And Application Of Halides And Sulfates As Nonlinear Optical Materials

The nonlinear optical effect was first discovered in 1961,which started the exploration and research of nonlinear optical(NLO)materials.The discovery has been developed for nearly 60 years.Scientific researchers have discovered many kinds of nonlinear optical materials,which are widely used in military,medical,communication and other fields.Nonlinear optical materials can be classified into mid-infrared band(?800nm),visible region(400-800nm),ultraviolet region(?200nm).Halides belong to nonlinear optical materials in mid-infrared band,sulfate belongs to nonlinear optical materials in deep ULTRAVIOLET band.This paper introduces the exploration of two halides in nonlinear optical properties and sulfate in nonlinear optical properties and is divided into three chapters,the main research content and innovation of each chapter is as follows:In this thesis,we design and synthesize halides and sulfides as new second-order nonlinear optical crystal materials.The main research uses metals with d10configuration and lone pair electrons as the central atoms based on the following considerations:(1)halides tend to have large band gaps,which are favorable for high laser damage thresholds;(2)metal ions with d10 configuration and lone pair electrons are favorable for causing second-order ginger Taylor distortion,thus easily forming non-centrosymmetric structures and producing second-order nonlinear optical effects;(3)sulfates tend to have excellent birefringence properties.The main work is as follows:(1)Two organic-inorganic hybrid halide polycrystals[(C₂H₅)₄N]Sn Br3(Cmc2₁)and[(C₂H₅)₄N]Sn Br₃(Cc)were designed and synthesized by hydrothermal method.[(C₂H₅)₄N]Sn Br₃(Cmc2₁)and[(C₂H₅)₄N]Sn Br₃(Cc)with different crystal structures were obtained for the first time.Specifically,the number of anionic groups Sn Br₃-per unit volume of crystal structure was completely different.The SHG effect was 0.3(?)and 2.5(?)times of KDP,respectively.This is also confirmed by theoretical calculations of electronic structure.More importantly,two very important halide polycrystals were synthesized for the first time in this work,which provides a feasible way to detect novel NLO materials and other photoelectric functional materials.(2)A new anhydrous metal sulfate----KTb(SO₄)₂with noncentrosymmetric structure was synthesized by hydrothermal method.Its structure is characterized by a three-dimensional spatial network composed of adjacent[KO₄],[Tb O₈]and[SO₄]complexes.It has moderate frequency doubling effect in sulfate system,about 0.15times that of KDP,and high thermal stability,decomposition temperature up to 700?.In-depth theoretical calculation shows that the light response of KTSO mainly comes from the synergistic effect of[Tb O₈]and[SO₄].This work provides a new anhydrous sulfate structure,further enrichis the structure of sulfate system,and provides a new paradigm for the construction of new anhydrous NLO materials.(3)A new bromocadmium salt KRb₃Cd Br₆,a rare example of a mixed A-site cation with a wide infrared transmission range up to 14?m,was prepared in this chapter by a simple solution method based on a combined hard and soft acid-base pair theory.it has a UV-visible absorption cut-off of 466 nm,corresponding to an optical band gap of 2.66 e V.the crystal is thermally stable up to 630°C and is not hygroscopic.The crystal is thermally stable up to 630°C and is stable when exposed to air for a long time without moisture absorption and has good physical and chemical stability.Although the crystal is centrosymmetric and does not have second-order nonlinear optical effects,it is a rare case of mixed A-site cations in halide systems,and the crystal has certain advantages in terms of transmission range,optical band gap,and physicochemical stability,which provides a certain reference value for us to continue to explore second-order nonlinear optical crystal materials.