Syntheses And Characterizations Of Alkaline Earth Metal And Rare Earth Borate Halides

As important photoelectric functional materials,deep ultraviolet nonlinear optical（NLO）crystals have important applications in laser micromachining,high-density optical storage,and laser lithography,et al.In this paper,the main research goal is to design and synthesize new deep ultraviolet NLO materials.Alkaline earth metal and rare earth borate halides are selected as the main research system.Through traditional solid-state synthesis methods,eight new noncentrosymmetric（NCS）alkaline earth metal and rare earth borate halides have been successfully designed and synthesized.The systemic performance measurements show that they have a short UV cutoff edge（λ<190 nm）and large second-harmonic generation responses（2.3-6.4×KDP）,especially,the large second-harmonic generation responses of Ba₃La₄O₄（BO₃）₃Br up to6.4×KDP that is the largest among all reported deep ultraviolet NLO borate containing isolated BO₃ groups.In addition,combining structural analysis with theoretically calculations show that the halogen and rare earth cation have significant effect on their structures and performances.The main results and innovations are summarized as follows:1.Design and Performance Characterization of Deep UV Nonlinear Optical Crystal Sr₅RE（BO₃）₄X（RE=Y,La;X=Cl,Br）.Four NCS alkaline earth metal and rare earth borate halides Sr₅Y（BO₃）₄X（X=Cl,Br）and Sr₅La（BO₃）₄X（X=Cl,Br）have been successfully synthesized by introducing halogen anions into rare earth borates.Their structures consist of an open three-dimensional[Sr/Y（BO₃）]_∞framework and Sr₃X（X=Cl,Br）polar chains.These compounds have short UV cutoff edges and large second-harmonic generation responses（λ<190 nm,2.30-2.42×KDP）.In addition,the important influence of halogen-centered polar chains on structural symmetry has been studied in borates containing halogen-centered polar chains,which provides the guidance for the synthesis and design of polar structures.2.Synthesis and Study of Deep UV Nonlinear Optical Crystals Ba₃La₄O₄（BO₃）₃X（X=F,Cl,Br）and Sr₃La₄O₄（BO₃）₃Cl with Large Second-Harmonic Generation Response.Deep ultraviolet rare earth oxyborate halides Ba₃La₄O₄（BO₃）₃X（X=F,Cl,Br）and Sr₃La₄O₄（BO₃）₃Cl with planar BO₃ groups have been synthesized by adjusting the ratio of rare earth/boron through high-temperature solid-state reaction.These structures possess an open[O₄La₄]_∞three-dimensional framework composed of La-O polyhedral with one-dimensional halogen-centered polar chains filled in the tunnels of the framework.The performance measurements indicate that these compounds exhibit short UV cutoff edges and large second-harmonic generation responses（λ<190 nm,5.40-6.40×KDP）.Especially Ba₃La₄O₄（BO₃）₃Br exhibits the strongest second-harmonic generation response（6.40×KDP）in all deep ultraviolet nonlinear materials containing isolated BO₃ groups.The structure-performance relationship study and the first principles calculation have demonstrated that strong covalent La-O bonds and the immense difference of electronic density in La-based polyhedra are the main contribution to strong second-harmonic generation response,which provides a new idea for the design of deep ultraviolet nonlinear optical materials with high second-harmonic generation response.