The research group of Professor Wu Liming of Beijing Normal University has made progress in the field of deep UV nonlinear optical materials

Nonlinear optical (NLO) crystal can effectively expand the wavelength range of laser, which plays an important role in the field of modern laser science and technology Among them, deep ultraviolet (DUV) nonlinear optical crystal is one of the research hotspots in recent years As the deep UV frequency doubling materials have strict requirements on the properties of materials, such as the requirements of the materials with non centrosymmetric crystal structure, large second-order frequency doubling effect coefficient, ultra wide band gap (greater than 6.2ev), so far, only a small amount of borates, phosphates and carbonates meet the above requirements There is only one commercial material KBBF that meets the above requirements, but because it contains highly toxic beryllium element and has strong layered growth habit, it is difficult to grow large crystals, and its application is limited to some extent Therefore, the exploration and research of new deep UV nonlinear optical material system has important scientific significance and practical value From the point of theoretical calculation, Professor Wu Liming's research group, School of chemistry, Beijing Normal University, firstly calculated and studied the optical properties of po3f2 - group, such as dipole moment, energy gap and hyperpolarizability, by using quantum chemistry software packages such as Gaussin and VASP It was found that the relevant parameters were superior to those of PO43 - group Based on this, they predicted that Po 3F 2 - would become a new DUV NLO functional group Under this guidance, after in-depth investigation of more than 100 known monofluorophosphates and calculation and analysis of related electronic structures and optical properties, they proposed that (NH 4) 2PO 3F, (C (NH 2) 3PO 3F and NaNH 4po 3F · H 2O have the potential to become new deep UV nonlinear optical materials In order to confirm the theoretical work, they have successfully obtained these three kinds of crystals by hydrothermal synthesis, in which the single crystal size of nanh4po3f · H2O can reach 14 × 9 × 2.3mm 3 Interestingly, these compounds exhibit excellent nonlinear optical properties: the deep UV cutoff is less than 200 nm; the second-order frequency doubling response is strong (0.9-1.1 times of the reference material KDP and 0.2-0.3 times of the reference material BBO at 1064 and 532 nm respectively); the laser damage threshold is high (2.3-3.1 times of the KDP at 1064 nm) In this study, a new functional group po3f2 - which can be used in the deep UV region is proposed for the first time, providing a new direction for the exploration of deep UV nonlinear optical crystals This research work was recently published on chemistry of materials (DOI: 10.1021/acs.chemometer.8b03310) The school of chemistry of Beijing Normal University is the only unit Xiong Lin, Ph.D student of the school of chemistry, is the first author of the paper, and Chen Jie, Lu Jing and pan Chunya, Ph.D students of the school of chemistry, are the second, third and fourth authors in turn, completing the relevant experimental verification work The research is supported by NSFC.