Synthesis,and Properties Of Lone Pair Based Selenites And Iodates Optical Materials

The second-order nonlinear optical（NLO）crystals,as the key device of the solid-state laser,which can generate higher energy lasers through the method of second-harmonic generation（SHG）,are widely applied in the fields of communication,storage,medical treatment,military and industrial manufacturing.With the development of science and technology,the exploration of excellent NLO with transparency windows become one of the research hotspots in the field of optoelectronics.However,the mutually exclusive nature of NLO crystals requirements;i.e.,SHG coefficients are inversely proportional to the band gap-the larger the band gap,the smaller the SHG efficiency,make the synthesis of NLO materials with excellent performance still a huge challenge.The lone pair-based iodates and selenites are important classes of visible and mid-IR NLO materials because of their excellent NLO properties,including very strong SHG responses,wide transparent region from near-UV to mid-IR region,and high optical high damage thresholds.In this dissertation,two promising NLO crystals Li Zn（IO₃）₃and Li Cd（IO₃）₃are rationally designed by the aliovalent substitution strategy from the commercializedα-Li IO₃.Then,a new strategy that anion templates could effectively regulate the orientation of polar basic building units to realize centrosymmetric（CS）to noncentrosymmetric（NCS）transformation.The contribution of the arrangement of iodates to birefringence via cationic polyhedron regulation is revealed.Finally,we creatively design and synthesize the first two three lone-pairs cations coexisting NCS compounds via halogen regulation.The research content is divided into the following seven parts:1.In the introduction,we firstly introduce the research background and systematically summarize the current development of iodates and selenites,and then classify iodates in detail.Finally,the current problems in the field of NLO crystals as well as the topic and significance of this article are pointed out.2.Two new promising nonlinear optical（NLO）crystals Li M^II（IO₃）₃(M ^II=Zn and Cd)are rationally designed by the aliovalent substitution strategy from the commercializedα-Li IO₃with the perfect parallel alignment of IO₃groups.Compared with parentα-Li IO₃and related A₂^IM^IV（IO₃）₆,the title compounds exhibit more stable covalent3D structure,and overcome the racemic twinning problem of A₂^IM^IV（IO₃）₆.More importantly,both compounds inherit NLO-favorable structure merits ofα-Li IO₃and show comprehensive NLO properties superior toα-Li IO₃.3.Noncentrosymmetry（NCS）is the prerequisite for the generation of second-order NLO materials.However,only approximately 15%of the reported inorganic crystals are NCS.It is of both fundamental and applied importance to develop NCS crystals from the efficient strategy.Herein,A family of NCS iodates AM（IO₃）₃Cl（A=Rb,Cs;M=Al,Ga,Fe）were successfully developed via Cl^-anion template induced transformation from their corresponding CS A₂HM（IO₃）₆.It is found that anion template could effectively regulate the orientation of polar basic building units to achieve CS-to-NCS transformation.Remarkably,Al-and Ga-based compounds Rb Al（IO₃）₃Cl,Cs Al（IO₃）₃Cl and Cs Ga（IO₃）₃Cl exhibit the excellent NLO properties.This will pave a way for chemists and materials scientists to using more types of anion templates as directing agent to realize CS-to-NCS transformation for development of NCS materials.4.Two new NLO compounds（NH₄）（IO₂F₂）and（NH₄）₂H（IO₃）₂Cl were synthesized via cation substitution,and the reported crystal of K₂H（IO₃）₂Cl was also studied.The experimental results show that three compounds have large band-gaps（4.06,4.01 and 4.07e V）,high LDTs(70.86,79.53 and 83.68 MW cm^-2),strong SHG responses（3.5,10.0 and11.0×KDP）and good phase matching ability.Theoretical calculations show that the optical properties of the compounds are mainly determined by the IO₃group as well as F^-/Cl^-ions.5.By introducing highly coordinated Ba-and La-based MO_nCl_mpolyhedra into iodate system,five birefringent materials of metal iodate chlorides,namely,Ba（IO₃）Cl,Ba（IO₃）Cl（H₂O）,Ba₇（IO₃）₅Cl₉,La（IO₃）₂Cl and La₂（IO₃）₅Cl,which exhibit diversified structures with diverse M_xCl_yand M_x（IO₃）_ystructural motifs and tunable birefringence.Theoretical calculations show that the birefringence of this series of compounds is contrary to unit volume density of IO₃groups.Structure analysis found that the parallel arrangement of IO₃groups is conducive to generating a large birefringence,and the discrete arrangement will reduce the birefringence,confirming the nonnegligible impact of the IO₃groups orientation on birefringence.6.In recent years,after appreciate that multiple NLO-active structural chromophores can synergistically enhance the NLO properties,a variety of new NLO crystals with excellent properties were synthesized.However,whether or not three lone-pairs can sustain NLO performance is unkown.Herein,the first two three lone-pairs cations coexisting NCS compounds,Pb Bi（Se O₃）₂F and Pb₂Bi（Se O₃）₂Cl₃were successfully synthesized via halogen regulation.Remarkably,both compounds exhibit the excellent NLO properties,such as strong SHG response（10.5×and 13.5×KDP）,large birefringence（0.085 and 0.179）,large energy band-gaps（3.75 and 3.45 e V）,high LDTs（62.95 and 49.83 MW/cm²）and good physicochemical stability.Theoretical calculations show that the three lone pair electrons have a good synergistic effect,indicating that the compounds with multiple lone pair electrons coexisting are potential NLO materials.7.We summarize the main conlusions and further work to be studied.