Recent advances in ultraviolet and deep-ultraviolet second-order nonlinear optical crystals

Second-order nonlinear optical (NLO) crystals functioning in the ultraviolet (UV) and deep-ultraviolet (deep-UV) regions are critically important as frequency conversion materials for all-solid-state UV laser devices. In this review, we focus on recent studies of inorganic UV and deep-UV NLO crystals with wide UV transparency and SHG efficiency. Following an introduction describing crystal-design strategies for UV and deep-UV NLO materials, the manuscript is organized according to the type of inorganic anions (borates, carbonates, nitrates and phosphates). Special attention is given to the crystal structures, second-order NLO properties, and structure–property correlations. The concluding remarks highlight future prospects in the field, with emphasis on the superiority of the different types of UV and deep-UV NLO crystals and the importance of large-size crystal growth for practical application in electro-optic devices.