Mixed-Anion-Oriented Design of LnMGaSO (Ln = La, Pr, and Nd; M = Ca and Sr) Nonlinear Optical Oxysulfides with Targeted Property Balance.

Nonlinear optical (NLO) crystals are of importance on extending infrared (IR) laser wavelengths. Considering their performance drawbacks in commercial IR NLO crystals, a recent challenge in exploring new excellent IR NLO crystals is how to break the inherent conflict between a wide bandgap ( ≥ 3.0 eV) and large NLO effect ( ≥ 0.5 × AgGaS) and simultaneously enlarge the birefringence (Δ) for a requisite phase-matching (PM) behavior. For that reason, rational combination of mixed-anion functional groups into a crystal structure affords the successful design and synthesis of six LnMGaSO (Ln = La, Pr, and Nd; M = Ca and Sr) NLO oxysulfides. Among them, LaMGaSO satisfy the property-balance demand (: 3.21-3.27 eV and : 0.9-1.0 × AgGaS) as promising PM NLO crystals through gathering their property advantages between LaMGaO and LaMGaS by mixed-anion-oriented performance engineering. A study on the structure-property relationship indicates that heteroleptic (Ln/M)SO and GaSO anionic groups are proven as promising NLO-active units and offer a great synergistic effect on the NLO origin. This work as a visualized model not only provides a first clear cognition on varying properties from oxide to sulfide to oxysulfide but also highlights the feasibility of mixed-anion-oriented design of new NLO candidates with balanced performances.