Abstract
Exploration of nonlinear optical (NLO) crystals that are competent in generating short-wavelength ultraviolet (UV, λ ≤ 266 nm, and even deep-UV, λ ≤ 200 nm) coherent light output by direct second harmonic generation (SHG) remains a formidable challenge. Herein, four UV/deep-UV NLO crystals, M(2)B(4)SO(10) (M = K, Rb, and Cs) and Rb(3)B(11)PO(19)F(3), were successfully synthesized by evolving the KBe(2)BO(3)F(2) (KBBF) structure into mixed-anionic borosulfate and fluoroborophosphate systems. They display functional [B(4)SO(10)](∞) or [B(11)PO(19)F(3)](∞) KBBF-type layers that are composed of [BO(3)], [BO(4)], and [SO(4)] groups or [BO(3)], [BO(4)], [BO(3)F], and [PO(4)] groups, respectively. Experimental characterization and numerical computation results indicate that these crystals possess exceptional NLO performance, including large SHG responses (0.9-1.7 × KDP at 1064 nm and 0.1-0.3 × β-BBO at 532 nm) and adequate birefringence to fulfill the SHG phase-matching (PM) condition at 266 nm. In particular, the shortest type-I PM wavelength (λ(PM)) of Rb(3)B(11)PO(19)F(3) reaches 180 nm, which implies that Rb(3)B(11)PO(19)F(3) can become a prospective deep-UV NLO crystal. In addition, single crystals of K(2)B(4)SO(10), Rb(2)B(4)SO(10), and Cs(2)B(4)SO(10) are easily obtained by the high-temperature solution approach. This work will facilitate the discovery of short-wavelength PM NLO crystals by using the KBBF structure as the template.