Nonlinear-Optical Crystal Rb₃YB₆O₁₂ with Condensed B₅O₁₀ Blocks That Exhibits an Intriguing Structural Arrangement and a Short Ultraviolet Absorption Edge

Nonlinear-optical (NLO) crystals, which can regulate the laser wavelength through a cascading second-harmonic-generation technique, have been widely utilized in the field of optoelectronics. In this work, we grew the NLO borate crystal Rb₃YB₆O₁₂ (RYBO) using the spontaneous crystallization method. RYBO crystallizes in a chiral trigonal space group of R32 with a new type of structural arrangement built from Y–O short chains and B₅O₁₀ groups. It is significantly different from the known structure of chemical analogues Rb₃REB₆O₁₂ (RE = Nd, Eu) not only in the halved unit cell parameter but also in the Y–O connection manner. The NLO response of RYBO is about 0.8KDP, 8-fold larger than that of KB₅O₈·4H₂O with the same B₅O₁₀ groups because of the coexistence of two NLO-active units of the distorted YO₆ octahedra and B₅O₁₀ anions. Thanks to the short ultraviolet (UV) cutoff, RYBO may have potential NLO applications in the UV and even deep-UV spectral regions.