SrZnGeSe₄: a promising infrared nonlinear optical material with strong second harmonic generation and high laser-induced damage threshold

Developing new infrared (IR) nonlinear optical (NLO) materials with strong NLO response and wide band gap is highly desired in the NLO fields but challenging due to the contradiction between the two critical parameters. In this work, by optimizing the advantageous structural motifs, a new selenide IR NLO candidate SrZnGeSe₄ was rationally designed, fabricated, and validated in the experiment. Structurally, SrZnGeSe₄ is composed of [ZnSe₄], [GeSe₄], and [SrSe₈] units, resulting in a tunnel-like three-dimensional structure. The synergistic effect of polyhedral units in SrZnGeSe₄ gives rise to balanced optical properties, including a wide band gap (2.5 eV) in selenides, a strong NLO response (1.8 × AgGaS₂), and a high laser-induced damage threshold (3.3 × AgGaS₂). The density functional theory calculations uncover that the wide optical band gap and large NLO effect in SrZnGeSe₄ are primarily governed by the advantageous [ZnSe₄] and [GeSe₄] NLO-active units. The experimental and theoretical results indicate that SrZnGeSe₄ is a promising IR NLO candidate and give some new insights into the design of new IR NLO materials with high performance.