Novel [BO₂] Superhalogen Module-Enabled Deep-ultraviolet Nonlinear Optical Material: Rational Design for Tailored Birefringence and Phase Matching

Abstract

Deep-ultraviolet (DUV) nonlinear optical (NLO) crystals are the key materials to create the tunable DUV laser for frequency conversion technologies. Nevertheless, limited by the transparency range, very few crystals can satisfy this technical requirement and the innovation of the novel candidates have become a challenge for researchers. Hence, the studies to date have chiefly focused to find the next potential and competitive candidates by the change of coordination environment through highly electronegative anionic functional group. Herein, we introduce DUV-NLO concept through [BO2] unit by exploring new chemical space, and design a novel NLO crystal CsBe2B3O7 by combining molecular-engineering and the first principles calculation. CsBe2B3O7 with a new DUV NLO functional module [BO2] possesses excellent DUV optical properties such as a suitable SHG response ∼ 0.8 × KH2PO4 (KDP), short DUV cutoff edge of 192 nm and large birefringence 0.108@1064 nm. The optimized optical properties render CsBe2B3O7 a DUV frequency doubling ability close to its cutoff edge (∼192 nm).Additionally, the first-principles calculations demonstrate that our constructed [Be2B3O7] units maintain densely staked layered structure without F atoms. This work not only contributes to enlarge the structural and functional diversity but also provides a direction to the invention of novel high-performance NLO crystals with [BO2] unit.