Recent progress in borate-based short-wavelength nonlinear optical crystals with boron-oxygen skeleton modification

Ultraviolet (UV, & lambda; < 400 nm) and deep-UV (& lambda; < 200 nm) nonlinear optical (NLO) crystals have the ability to convert the wavelength of laser to output UV or even deep-UV coherent light by means of frequency doubling and play a significant role in solid-state lasers. Recently, borate-based short-wavelength NLO crystals have attracted considerable attention owing to their diverse structures and tunable performance. For example, fluorooxoborates, hydroxyborates, hydroxyfluorooxyborates, borophosphates, borosilicates, borosulfates and fluoroborophosphates display rich structure types and enhanced optical properties. In this review, recently discovered borate-based NLO crystals with a modified boron-oxygen skeleton are overviewed and analyzed, including their crystal structure features, short-wave cutoff edges, birefringence and second harmonic generation (SHG) responses. This review presents the positive influence of boron-oxygen skeleton modification on the structure-property relationship. We hope to provide the recent progress in the crystal chemistry of borate-based short-wavelength NLO crystals and facilitate the discovery of promising UV and even deep-UV NLO candidates.