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.

Recently, researchers of Research Center for Crystal Materials successfully synthesized four UV/deep-UV NLO crystals, M₂B₄SO₁₀ (M = K, Rb, and Cs) and Rb₃B₁₁PO₁₉F₃ by evolving the KBe₂BO₃F₂ (KBBF) structure into mixed-anionic borosulfate and fluoroborophosphate systems. They display functional [B₄SO₁₀]_∞ or [B₁₁PO₁₉F₃]_∞ KBBF-type layers that are composed of [BO₃], [BO₄], and [SO₄] groups or [BO₃], [BO₄], [BO₃F], and [PO₄] 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 Rb₃B₁₁PO₁₉F₃ reaches 180 nm, which implies that Rb₃B₁₁PO₁₉F₃ can become a prospective deep-UV NLO crystal. In addition, single crystals of K₂B₄SO₁₀, Rb₂B₄SO₁₀, and Cs₂B₄SO₁₀ 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.

This work was published in ACS Central Science as a Research Article (ACS Cent. Sci. 2022, 8, 11, 1557–1564).

This work was supported by This work was supported by the National Natural Science Foundation of China (61875229, 61922084, 51972336, and 61835014), the West Light Foundation of CAS (2019-YDYLTD-002), the Instrument Developing Project of CAS (GJJSTD20200007), the International Partnership Program of CAS (1A1365KYSB20200008), and the Xinjiang Major Science and Technology Project (2021A01001). The authors gratefully acknowledge the reviewers for their valuable comments and suggestions, which are beneficial to improving the manuscript.

Article：https://doi.org/10.1021/acscentsci.2c00832