The Large Second-Harmonic Generation of LiCs2 PO4 is caused by the Metal-Cation-Centered Groups

Discovery of First Magnesium Fluorooxoborate with Stable Fluorine Terminated Framework for Deep-UV Nonlinear Optical Application

The generated light can be tuned to cover almost the entire spectral range from deep-ultraviolet to terahertz wavelengths by utilizing the nonlinear optical crystals with a simple frequency doubling process. Among them, the discovery of novel candidates for the production of deep-ultraviolet light is by extension a great challenge toward realizing the vast potential. Actually, the availability for this process mainly depends on whether the critical performance can be well coexisted in one practical crystal. Herein, the first magnesium fluorooxoborate MgB₅ O₇ F₃ was synthesized as a new competitive candidate for deep-ultraviolet nonlinear optical application. It has a sufficiently large nonlinearity and a deep-ultraviolet phase matching wavelength, indicating that it holds great potential for the production of coherent light below 200 nm. The critical performance enhancement of MgB₅ O₇ F₃ when compared with its isomorphic phases was demonstrated and discussed. More importantly, we proposed that fluorooxoborate system with the general formula of MB₅ O₇ F₃ (M=divalent metal) possesses stable fluorine terminated framework, which makes them tend to retain their crystallized space groups unchanged.

Uncovering a Functional Motif of Nonlinear Optical Materials by In Situ Electron Density and Wavefunction Studies Under Laser Irradiation

Exploring nonlinear optical (NLO) functional motifs (FM, the structural origin of NLO efficiency) is vital for the rational design of NLO materials. Normal spectrum techniques applied in studying photon exciting materials are invalid for NLO materials, in which electrons are not excited substantially but only distorted under laser. A general strategy of determining NLO FM is proposed by comparative studies of experimental electron density (ED) without and under the laser. The in situ experimental ED and wavefunction of typical NLO material LiB₃ O₅ (LBO) under dark and 360 and 1064 nm lasers are investigated. Compared with the initial state under dark, the ED of [B₃ O₅ ]^- unit at functional states under laser irradiation exhibits remarkable changes of topological atomic and bond properties, confirming the NLO FM being [B₃ O₅ ]^- . The work extracts for the first time the FM of a NLO material experimentally and highlights the crucial role of in situ ED analysis in studying NLO mechanisms.

Syntheses, structures and characterization of non-centrosymmetric Rb2Zn3(P2O7)2 and centrosymmetric Cs2M3(P2O7)2 (M = Zn and Mg)

Three phosphates Rb₂Zn₃(P₂O₇)₂ and Cs₂M₃(P₂O₇)₂ (M = Zn and Mg) were successfully synthesized by a high-temperature solution method.