Rational Design of a Deep-Ultraviolet Nonlinear Optical Crystal

Rational structural design of inorganic materials remains a significant challenge in materials science, particularly for deep-ultraviolet (DUV) nonlinear optical (NLO) crystals. Herein, a new DUV-transparent NLO borate, CsSrB₃O₆ (CSBO), has been successfully predicted and synthesized by the cation regulation from Cs₂KY(B₃O₆)₂ (CKYBO). The structural stability of CSBO was confirmed by first-principles phonon vibration calculations, and it was eventually synthesized via a high-temperature solid-state reaction. The substitution of K⁺/Y³⁺ cations with Sr²⁺ cations eliminates the disorder and significantly reduces the thermal expansion anisotropy (CKYBO: 9.32, CSBO: 1.95), which effectively protects the crystals from cracking during crystal growth. Furthermore, CSBO successfully achieved the ordered design of B₃O₆ functional groups, and this structural feature enables it to display well-balanced functional performance, including a strong second-harmonic generation response (5.0 × KH₂PO₄), a short UV absorption edge (<190 nm), and moderate birefringence (0.075@1064 nm). All of these results demonstrate that CSBO is a promising DUV NLO material, and this study establishes an effective strategy for developing high-performance NLO crystals through synergistic computational-experimental approaches.