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

Abstract 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 MgB 5 O 7 F 3 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 MgB 5 O 7 F 3 when compared with its isomorphic phases was demonstrated and discussed. More importantly, we proposed that fluorooxoborate system with the general formula of MB 5 O 7 F 3 (M=divalent metal) possesses stable fluorine terminated framework, which makes them tend to retain their crystallized space groups unchanged.