Professor Wu Liming and Professor Chen Ling of Beijing Normal University have made progress in the field of deep UV nonlinear optical materials

Deep ultraviolet (wavelength < 200 nm) nonlinear optical material is one of the key points of scientific research and practical application in recent years Since the first case of ba3p3o10x (x = Cl, BR) was reported in 2014 by Professor Wu Liming's group and Professor Chen Ling's group in the school of chemistry, Beijing Normal University (j.am Chem SOC 2014, 136, 4807), the phosphate system has become a hot spot in the research of deep UV nonlinear optical materials It is very difficult and challenging to study the new generation of deep UV nonlinear optical materials The difficulty lies in the strict requirements for the structural properties of this kind of materials, that is, how to integrate multiple properties such as non central symmetry, large second-order nonlinear optical response, deep UV region transparency, phase matching and large laser loss threshold into the same structure at the same time The deeper understanding of the relationship between microstructures requires higher requirements On the basis of the previous work, Professor Wu Liming's group and Professor Chen Ling's group in the school of chemistry of Beijing Normal University adopted the method of solid-phase synthesis to obtain the novel BA 2naclp 2O 7 crystal material, which is the first BA 2tiosi 2O 7 structure that can realize phase matching The material shows excellent nonlinear optical properties: the transparent region reaches the deep ultraviolet region, the absorption edge is less than 176 nm; the second-order frequency doubling effect is about 0.9-1.3 times of potassium dihydrogen phosphate (KDP); the laser damage threshold is about 1.4 times of KDP What's more interesting is that BaTiO structural materials are usually typical small birefringence materials, while ba2naclp2o7 can still achieve laser phase matching behavior while maintaining this structure Combined with theoretical calculation and crystal structure analysis, they found that the mechanism of realizing phase matching is that the disordered distribution of bridging oxygen in the [P2O7] 4-group destroys the crystal's microsymmetry, further induces the splitting of energy band degenerate energy level, so as to increase the material's refractive index n x and decrease its n y, and finally leads to the expansion of the crystal's birefringence Δ n from 0.003 to 0.017 , enter the birefringence range where phosphate can achieve phase matching (PM) It is the first time that the disorder of crystal structure leads to the phase matching of materials, and the microscopic mechanism is clarified This discovery has opened up a new way to realize the control of material birefringence This research work was recently accepted and published by J am Chem SOC (DOI: 10.1021 / JACS 8b10209) The school of chemistry of Beijing Normal University is the only unit Chen Jie is the first author of the thesis, and Xiong Lin is the second author of the thesis The research is supported by NSFC.