Application Of Cystal Materials Containing D~0 Transition Metal In Laser Frequency Doubling

Inorganic crystalline materials have been well applied in a wide range of fields including electrochemistry materials,fluorescent materials,birefringent optical materials,nonlinearoptical(NLO)materials,etc.In recent years,great efforts have been made to develop NLO materials because of their attractive performances and significant applications for laser frequency conversion.Among them,second-order NLO crystal materials are one of the fastest developing and most widely used.Infrared NLO materials which can obtain sdjustable infrared has attracted much attention in the military and civil fields laser.So far,IR NLO crystals include AgGaS2(AGS).AgGaSe2(AGSe),and ZnGeP2(ZGP)are the most successful commercial NLO crystals.However,these IR NLO crystals cannot strictly meet the requirement of practical applications mainly because of their low laser-induced damage thresholds(LIDTs)and double photon absorption.According to literature reports,we found that the introduction of d0 transition metal cations is conducive to the formation of rich and diverse acentric structures.Therefore,it is urgent to design and explore new infrared NLO materials with reasonable and effective synthesis strategies.Especially,the second-order Jahn-Teller(SOJT)distorted MO6 octahedra(M=Ti4+,Zr4+,Nb5+,Ta5+,Mo6+,W6+,Te6+,etc.)can increase the structural distortion,and obtain good NLO crystal materials.So,we try to explore d0 transition-metal to obtain some new types of crystals with acentric structures and good NLO properties.In addition,we also consider combining potential anions to construct structural units.F is the most electronegative element in the periodic table and F atom can bond to metal cations with strong bond interaction,which is helpful for obtaining compounds with large band gaps and thus high LIDT.Sulfides are considered as one of the most IR NLO crystals candidates for excellent SHG effect and wide transparent range.Moreover,O atom.as a more electronegative atom,can improve the band gap and further increase LIDT.Therefore,special crystal structuresattractive physical properties and he balance between SHG and LIDT can be achievedbecause of the different electronegativity and bonding characters of O and S atoms.Therefore,on the basis of introducing d0 transition metal,we respectively combine F,S and O element into compounds to studying new NLO crystal materials.The specific works are as follows:(1)A novel d0 transition metal fluoride,CsNaTaF7,was obtained by hydrothermal method.It is crystallized in the noncentrosymmetric space group Cmc21 of the orthorhmbic system.The crystal structure can be described as a 2D{[NaTaFi2]6-}? layer constructed by the(NaF7)6and(TaF7)2-units with the Cs+ cations reside in the 3D framework and make an overall charge balance.Under 1.064,um laser irradiation.CsNaTaF7 powder sample show a SHG response of 0.2 times than that of KDP.Besides,it is phase matching.The theoretical calculation shows that the band gap is mainly determined by Ta-5d and F-2p orbitals.which is consistent with the experimental values.(2)In order to obtain novel NLO crystal materials,we designed new compounds based on the strategy of different cationic valence substitution and congener substitution to optimize the structure and properties on the basis of the parent structure.Here,a mixed alkali metal and d0 transition-metal fluoride,namely,KNa2ZrF7,was obtained by a facile hydrothermal method.It crystallizes in an orthorhombic system with the polar space group Pmn21,and its pseudo1D structure features isolated[ZrF7]moncocapped trigonal prisms,which are ionically linked together by countercations K+and Na+,representing a new type of fluoride.The powder sample of KNa2ZrF7 exhibits a moderate second-harmonic-generation response(0.4 × KDP)and a high LIDT.Besides,it can realize phase matchability and possesses a wide-IR transparent window.Thermal stability analysis suggests that KNa2ZrF7 is a congruent compound.Structural comparisons with related fluorides and theoretical calculations are also presented in this work.(3)Since CsNaTaF7 and KNa2ZrF7 do not show satisfactory SHG effect,we design oxysulfides to obtain crystal materials with good SHG effect and high LIDT.Here,two oxysulfides,Sm3NbS3O4 and Gd3NbS3O4,are obtained by solid-state reactions.Both of them crystallize in the polar space group Pna21,and the anionic frameworks are built by isolated distorted[NbS2O4]octahedra.Sm3NbS3O4 and Gd3NbS3O4 exhibit phase-matchable secondharmonic-generation(SHG)effects of about 0.3 and 0.4 × AGS at 2.1?m,and high powder LIDT values of 12.5 and 4.5 times that of AGS.Gd3NbS3O4 shows antiferromagnetic behavior while Sm3NbS3O4 exhibiting typical Van Vleck-type paramagnetism.Moreover,the bandgap of Sm3NbS3O4 and Gd3NbS3O4 are 2.08 and 2.13 eV,and they exhibit broad transparent ranges.[NbS2O4]octahedron was first used as a SHG-active motif for NLO materials.A systematic analysis of crystal structures,NLO performances,and magnetic behaviors,as well as firstprinciples theoretical studies,is presented.This work enriches the study on relatively rarely explored NLO-active metal oxysulfides.