Exploration,Synthesis And Properties Of New Birefringent Group And Composite Metal Borate Optical Crystals

Ultraviolet/deep ultraviolet crystals have special significance for solid-state lasers with different frequencies and polarizations,while the birefringent group was also important for the birefringence crystals.This paper aims to explore new birefringent group and synthesize new ultraviolet/deep ultraviolet crystal materials,focusing on boron-nitrogen system and composite metal borate system.Through systematic investigation and experimental exploration,the contribution of BN₂group to birefringence was screened,while three borate compounds were designed and synthesized,including Li₇M^IISc B₁₂O₂₄(M^II=Sr,Ba_0.6Ca_0.4)andβ-Rb₃Cd B₅O₁₀.Their optical properties were evaluated by theoretical calculation and experimental characterization,and the relationship between their structures and optical properties was studied.The main research contents are as follows:1.Based on the strategy of the planarπ-conjugated group beneficial to produce large birefringence in optical functional materials,the boron-nitrogen system was mainly studied,then a new birefringent BN₂group was explored.Based on the fact that inorganic planarπ-conjugated groups are beneficial to produce large birefringence in optical functional materials,and whether linear groups can be used as gain groups to generate large birefringence remains to be studied.This paper is mainly studied the boron-nitrogen system,and found that linear BN₂group can produce large birefringence.A series of compounds with linear BN₂groups were screened,whose molecular formula were A₃BN₂（A=Li,Na）,A₃BN₃（A=Mg,Ca）and Ba₃（BN₂）₂.In particular,Ca₃（BN₂）N shows a large birefringence about 0.411 at 1064 nm,expected to be a new birefringent crystal material.The results show that the BN₂group can significantly affect birefringence owing to its structure arrangement and large optical anisotropy,which will be a new type of birefringence enhancement group.2.Composite alkali metal,alkaline earth metal and rare earth metal borates Li₇M^IISc B₁₂O₂₄(M^II=Sr,Ba_0.6Ca_0.4)with deep ultraviolet cutoff edge were designed and synthesized.Two cases of isomeric center symmetric rare earth borate Li₇M^IISc B₁₂O₂₄(M^II=Sr,Ba_0.6Ca_0.4)were obtained by combining alkali metal,alkaline earth metal and rare earth metals by high temperature solution method.They have a three-dimensional anion framework structure[Sc B₁₂O₂₄]composed of the[B₆O₁₄]group and[Sc O₆]octahedron.The results show that Li₇M^IISc B₁₂O₂₄(M^II=Sr,Ba_0.6Ca_0.4)have a deep ultraviolet cutoff edge（<200 nm）.The combination of alkali metal,alkaline earth metal and rare earth metal can adjust the blue shift of the cutoff edge,and the results further expand the structural chemistry of borate system.3.A new phase of Rb₃Cd B₅O₁₀with short ultraviolet cutoff edge was designed and synthesizedA new central symmetric borate crystalβ-Rb₃Cd B₅O₁₀has been synthesized by high temperature solution method.The crystal has a two-dimensional[Cd B₅O₁₀]_∞layered structure formed by the[B₅O₁₀]group interlinked with the[Cd O₄]polyhedron.This transition occurs within the same space group,and the results show thatβ-Rb₃Cd B₅O₁₀exhibits clear irreversible phase transition.Meanwhile it has the shortest ultraviolet cutoff edge（198 nm）among the known cadmium-containing borate.The results further enrich the structural chemistry of borate system.