Synthesis,Structure And Properties Of Lead Beryllium Borate Ultraviolet Optical Crystals

Ultraviolet nonlinear optical crystal materials can emit lasers with coherently tuned wavelengths through the second harmonic effect,and are the core part of solid-state laser systems.The synthesis and preparation of new ultraviolet nonlinear optical crystals play an important role in promoting the development of laser science and technology.In this dissertation,the high-temperature melting synthesis technology was used to introduce Pb²⁺ions containing lone pairs of electrons into the beryllium borate.Finally,three new cases of lead-beryllium borate ultraviolet nonlinear optical crystals were synthesized,and their structures and nonlinear optical properties were compared and analyzed.(1)A chemical molecular-modified strategy was successfully used to synthesis a new UV NLO beryllium borate crystal,Sr₂Pb(Be B₅O₁₀)(BO₃)(SPBBO),through the high-temperature molten method,based on a K₃B₆O₁₀Cl-perovskite-like structure model.The compound crystallizes in the acentric trigonal space group R3m,and exhibits a 3D framework composed of Be B₅O₁₃anionic groups.The open framework has the cavities filled by cationic Sr/Pb and anionic BO₃groups.Compared with the structure of K₃B₆O₁₀Cl,BO₄group is replaced by(Be/B)O₄,K ion is replaced by Sr/Pb,and Cl ion is replaced by BO₃group.This modification strategy significantly improved SHG efficiency of about 8×KDP and the birefringence value is discovered up to be 0.1,which benefitting from Pb-modified p-?interaction and Pb-6s²active lone pair.Therefore,SPBBO overcomes conflicting nature among strong second harmonic generation(SHG)response,large birefringence,and short UV absorption edge and band-gap.The thermal stability of SPBBO crystal can reach 897?,with excellent thermal stability.Meanwhile,single-crystal of SPBBO exhibits an outstanding laser-induced resistant behavior,with particularly high LIDT of 2100 MW cm^-2,which is promising for use as high-power NLO applications.The excellent properties indicate that SPBBO is very promising for next-generation UV NLO materials.The successful molecular-modified strategy opens a door to rationally design new NLO functional materials with expected propertiesresistance.(2)We designed and synthesized two new cases of lead beryllium borate nonlinear optical crystals,Pb Be₂B₂O₆and Pb Be B₂O₅.Pb Be₂B₂O₆crystallizes in the acentric trigonal space group Pmn2₁.The compound shows the two-dimensional[Be BO₃]_?layer stacking frame formed by Be BO₆anion groups sharing the corners among them.Pb atoms are filled between layers to construct the entire three-dimensional structure.In this structure,Be-O ultra-long bond length with ionic characteristics is 2.18(3)?.The asymmetric Pb O₄group connects with two BO₃triangles sharing the edges,which can produce synergistically interact,and Pb have the stereochemicallyactive lone pair.These structural features are conducive to the crystal having a large second harmonic generation response and large birefringence.The thermodynamic performance test shows that it has a good thermal stability up to 852?.The ultraviolet-visible diffuse reflectance spectrum shows that the ultraviolet cut-off edge can reach 305 nm,and band gap value is 3.84 e V.Nonlinear optical property measurement initially shows that it has strong SHG response approximately 8.9×KDP at 1064 nm and large birefringence of 0.086.It initially shows that Pb Be₂B₂O₆crystal has excellent potential as an ultraviolet nonlinear optical crystal material.Pb Be B₂O₅crystallizes in the chiral space group P2₁2₁2₁.The crystal structure is composed of two-dimensional[Be B₂O₅]_?layers.The structure is characterized by a Be O₄tetrahedron,BO₃triangle and BO₄tetrahedron co-oxygen connection to form six-membered ring Be B₂O₈anionic group.Then every Be B₂O₈groups are further connected with the neighbouring six same rings to form a two-dimensional[Be B₂O₅]_?layered network structure.Pb atoms are filled between layers with Pb O₄twisted polyhedron.The thermodynamic performance test shows that there is no weight loss to 920?,showing good thermal stability.Nonlinear optical property testing preliminarily shows obvious second harmonic generation response.Through comparative analysis with known compounds,it is found that Pb ions have the template effect of structure-induced noncentre,which provides an idea for the exploration of new acentric functional crystal materials.