M2As2Q5 (M = Ba, Pb; Q = S, Se): a source of infrared nonlinear optical materials with excellent overall performance activated by multiple discrete arsenate anions.

The introduction of coordination polyhedra containing stereo-chemically active lone pairs into the chalcogenide structures is beneficial for realizing centric-to-acentric structural transformation and further enhancing the second-harmonic generation (SHG) efficiency (d_ij) and the birefringence (Δn) for IR nonlinear optical (NLO) applications; however, this has been rarely reported. Herein, non-centrosymmetric (NCS) arsenates M₂As₂Q₅ (M = Ba, Pb; Q = S, Se) have been screened out by combined experiments and theoretical calculations as a new source of IR NLO materials. Interestingly, they feature unique zero-dimensional structures containing diverse types of discrete As-based coordination polyhedra with M²⁺ cations located among them, which is discovered for the first time in the IR-NLO chalcogenides. More significantly, they all exhibit multiple key NLO parameters for practical applications in the IR region, including wide phase-matching ranges (>950–1370 nm), remarkable d_ij (1.0–2.7 × AgGaS₂) and large laser-induced damage thresholds (LIDTs = 6.8–12.4 × AgGaS₂). Theoretical studies demonstrate that the discrete As-based coordination polyhedra play a critical role in the linear optical and NLO responses of the title compounds. We believe that this work can not only enrich the diversity of NLO-active groups, but also provide a new choice for material design in NCS chalcogenides. [ABSTRACT FROM AUTHOR]