The ideal infrared (IR) nonlinear optical (NLO) crystal must have a broad transmittance range, a high laser-induced damage threshold (LIDT), a high birefringence index, bulk single-crystal form, and physicochemical stability.
However, a trade-off between a high NLO coefficient and a broadband gap frequently makes it difficult to obtain both features in a single material.
Recently, a research group led by Prof. Guocong Guo of the Chinese Academy of Sciences' Fujian Institute of Research on the Structure of Matter revealed two unique non-centrosymmetric chalcogenides: M[M4Cl] [Ga11S20] (M=A/Ba, A=K, Rb) as superb nonlinear optical crystals.
The study was published in Small on September 11, 2023.
M[M4Cl] [Ga11S20] (M=A/Ba, A=K, Rb) are the first salt-inclusion chalcogenides with diamond-like anionic frameworks produced via a cationic substitution method.
Researchers formerly considered typical diamond-like chalcogenides viable candidates for IR NLO materials. However, due to their small band gaps, they frequently display restricted LIDTs.
To produce two novel salt-inclusion sulfides, the researchers used an unorthodox cationic substitution technique, [[SZn4] S12 + [S4Zn13] S24 + 11ZnS4 => MS12+ [M4Cl] S24 + 11GaS4], M[M4Cl] [Ga11S20] (M=A/Ba, A=K, Rb). As predicted, adding mixed cations to the GaS4 anionic frameworks resulted in broadband gaps (3.04 and 3.01 eV) and enhanced high LIDTs (9.4 and 10.3×[email protected] μm).
Furthermore, the researchers discovered that the ordered arrangement of tetrahedral GaS4 units favored significant second-harmonic generation intensities (0.84 and 0.78×AgGaS2@2.9 μm).
The study shows how a cationic substitution technique based on diamond-like structures can manufacture high-performance NLO materials.
Journal Reference:
Lou, X.-Y., et al. (2023) Excellent Nonlinear Optical M[M4Cl] [Ga11S20] (M=A/Ba, A=K, Rb) Achieved by Unusual Cationic Substitution Strategy. Small. doi:10.1038/s41565-023-01436-w
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