Design,Synthesis,Structure And Properties Of Metal Halides As Mid-infrared Nonlinear Optical Materials

Nonlinear optics(NLO)crystal material can be used as a laser frequency conversion material to have a special role in the laser field,such as laser communication,eye surgery,laser ranging and high-energy laser weapons.With the development of science and technology,the requirements for laser intensity are getting higher and higher,so there is an urgent need for nonlinear optical crystal materials with excellent performance.Especially the exploration of NLO crystals in the deep ultraviolet and mid(far)infrared bands is extremely important.This paper aims to design and synthesize new type of halides as mid-infrared nonlinear optical crystal materials.The main research object is the halide with the metal by using the lone electron pair or the d¹⁰cation as the central atom.The main strategies are as follows:1)The halides are mostly an insulator with a larger band gap and thus a higher Laser damage threshold;2)Metals with lone pairs or d¹⁰cations facilitates the obtaining of distorted[MX_n]polyhedra,resulting in asymmetric structures on a macroscopic;3)Controllable substitution of halogens provides the basis for the design of halogenates with specific properties.The main work is as follows:(1)A new compound Rb₂CdBrI₃was successfully synthesized in a controlled manner with Cd²⁺with the electronic structure of d¹⁰as the central metal element,using reasonable halogen substitution.Compared with the isomorphic Rb₂CdBr₂I₂,the band gap of RbCdBrI₃was abnormally increased,about 4.01 e V,the laser damage threshold reaches 46 times that of AgGaS₂,and its powder frequency doubling effect can reach 2 times that of KDP,and it can achieve phase matching.It has a wide transparent range(2.5?20?m),good thermal stability(up to 556°C).(2)Through ICSD and literature research,we found that a Pb₇F₁₂Cl₂with a lone pair of Pb²⁺as the central metal element can be used as a promising infrared nonlinear optical material.A series of characterizations and performance testing have been done.The experiment results show that its powder frequency doubling effect is 1.6 times that of KDP,and can achieve phase matching.The infrared transmission can reach 20?m.Its band gap is calculated by ultraviolet absorption spectroscopy to be 4.5 e V.The preliminary test of its laser damage threshold(LDT)is about It is 80 MW/cm²,which is much larger than AgGaS₂(the commercialized infrared NLO material,5.2 MW/cm²measured under the same conditions).(3)A series of organic-inorganic hybrid materials were designed and synthesized with Ga and In of IIIA group as the central metal elements,namely,[(C₂H₅)₄N]InCl_4-xBr_x(x=0,2,4)and[N(CH₃)₄]MX₂(M=Ga,In;X=Cl,Br).For the former,with the substitution of Br for Cl,its nonlinear performance increases successively to 0.5,0.7,0.8×KDP,and its band gap decreases successively to 4.30,3.55,2.85 e V.The relationship between the halogen composition and band gap,optical anisotropy and frequency doubling effect was evaluated by first principles calculations.For[N(CH₃)₄]MX₂(M=Ga,In;X=Cl,Br),through the substitution of halogens,an interesting structural transition occurs,from bromide with an centrosymmetric space group of P4₂/m to chloride with a nocentrosymmetric space group of P-42₁m.At the same time,its optical band gap,thermal stability and birefringence have all undergone interesting changes.This series of work provides typical examples for exploring organic-inorganic hybrid Ga/In halides,and also lays a foundation for exploring and designing novel organic-inorganic hybrid halides for future optoelectronic applications.