LnMg6Ga6S16 (Ln = Nd, Sm), two bifunctional optical materials exhibiting both nonlinear optical and photoluminescent properties.

Low-oxidation-state rare-earth (RE) compounds, particularly divalent RE ions, possess unconventional electronic configurations that unlock novel catalytic, magnetic, and photoluminescent properties. However, the intrinsic instability of RE2+ ions has persistently hindered the development of stable divalent rare-earth chalcogenides. Herein, we surmount this challenge through the successful synthesis of two innovative compounds, LnMg6Ga6S16 (Ln = Nd, Sm), crystallizing in a noncentrosymmetric hexagonal P6̄ space group. The architecture reveals a three-dimensional framework constructed by [Mg-S]∞ framework coupled with [GaS3]∞ single and [Ga2S5]∞ double chains, with Ln2+ atoms occupying the interstitial spaces. Capitalizing on the noncentrosymmetric structure and divalent rare-earth ions, these materials exhibit remarkable dual functionality, pronounced nonlinear optical properties and distinctive photoluminescence. Comprehensive characterization reveals that LnMg6Ga6S16 exhibits exceptional properties, including a strong second-harmonic generation response (0.5 × AgGaS2), wide optical band gaps (≥3.0 eV), broad infrared transparency spanning up to ∼20 μm, and bimodal near-infrared photoluminescence across both the NIR-I and NIR-II spectral regions under UV excitation. Such a suite of capabilities enables LnMg6Ga6S16 to achieve an uncommon multifunctionality in infrared optics, which stems from the strategic incorporation of divalent lanthanide ions into a structurally tailored chalcogenide lattice and positions it as a highly promising candidate for advanced applications.