Synthesis And Optical Properties Researches Of Iodate-Halides

Mid-infrared（IR）laser has significant applications in many fields involving national defense,medical treatment,communication and laser processing,etc.Nonlinear optical（NLO）crystals capable of expanding the spectral ranges of all-solid-state lasers by a second-harmonic-generation（SHG）process play a crucial role in laser science.Over the past several decades,NLO crystals used in mid-IR bands are rare,which are mainly chalcopyrite-type semiconductor crystals,such as Ag Ga X₂（X=S,Se）and Zn Ge P₂.These materials have the advantages of large SHG effect and wide infrared transmission.However,they suffer from low laser damage thresholds（LDTs）and strong two-photon absorption,which is not conducive to high power laser output.Recent studies show that iodates and halides are two important mid-IR NLO crystals systems.Therefore,this research goal focuses on developing new mid-IR NLO crystals by combining iodates and halides.By traditional hydrothermal method,we have successfully synthesized seven crystals containing iodate units and oxygen-halide group.The general rules of designing and synthesizing new metal iodate-halide have been clarified in accordance with the structure-properties relationship.In addition,two new iodate crystals without halogen anions and a porous halide crystal with novel structure were obtained.The research achievements are as follows:1.Transition metal（TM）-containing iodate-halides crystalsFirstly,cations with second-order Jahn-Teller（SOJT）effect are able to exhibit giant microscopic acentricity.Then,halogen anions with high electronegativity can enlarge band gap,widen transmission band and improve laser damage threshold of materials.Therefore,it is an effective strategy to design mid-IR NLO materials with large second-order NLO coefficients by introducing the TM cations and halogen ions.Based on above idea,we have synthesized four novel TM-containing iodates-halides,Cs VF₂（IO₃）（IO₄）,Cs[V₃O₆F（IO₃）₃],Ba Nb OF（IO₃）₄ and Ba[Ti₂O₃F（IO₃）₃].Besides,we have also synthesized a TM-containing iodates without halogen anions,Ba Mo O₂（IO₃）₄.They will further enrich TM-containing iodates system.We have obtained some influence rules of the molar ratio between iodate units and TM cations on the dimension of structural basic build units.It is of great significance for designing mid-IR NLO crystals with specific structure and excellent comprehensive performance.2.Main-group metal（MM）-containing iodate-halides crystalsMM cations,such as In³⁺and Sn⁴⁺,can exhibit similar coordination with the TM cations and the substitution of MM cations for the TM cations can remove the d-d electronic transition and increase the band gaps and LIDTs.Then,as mentioned above,the advantages of the halogen anions are obvious.Based on this idea,we have synthesized three novel MM-containing iodates-halides,Ba[In F₃（IO₃）₂]、Ba[Sn F₂（IO₃）₄]and Na₃[In F₂（IO₃）₄].Besides,we have also synthesized a MM-containing iodates without halogen anions,K₂Sn（IO₃）₆.Ba[In F₃（IO₃）₂]and K₂Sn（IO₃）₆ crystallizes in NCS space group.Ba[In F₃（IO₃）₂]is composed of 1D[In F₄（IO₃）₂]_∞chain and Ba²⁺cations.Ba[In F₃（IO₃）₂]shows moderate SHG efficiency（1.4×KDP）,wide transmittance range（0.28～12.03μm）and large birefringence（0.172@1064 nm）.As is well-known,compounds with large band gaps usually exhibit small NLO coefficients.In this work,we put forward an effective design idea to balance above-mentioned conflicting factors:substituting the TM cation with the MM cation and partially substituting the oxygen ion with the halogen anion.3.Porous halide crystal with novel structureIn above researches,a new IR transparent porous metal-halide,In[Ba₃Cl₃F₆],has been synthesized.It features a 1D[Ba₆Cl₆F₁₈]_∞6-members channel with a pore size of4.88 nm.In[Ba₃Cl₃F₆]possesses wide spectral range from 0.366 to 22μm and favorable thermal stability of up to 650℃.Furthermore,the structural porosity of In[Ba₃Cl₃F₆]has been proved by the physical adsorption experiment,which indicates that In[Ba₃Cl₃F₆]is a potential halide molecular sieve.This research will open new opportunities for metal halides as IR-transparent molecular sieves.