SrZnGeSe4: An Infrared Nonlinear Optical Crystal Material with Wide Transmission Range and Large SHG Response

Through exploring the relationship between structure and performance, herein, a novel infrared (IR) nonlinear optical (NLO) crystal, SrZnGeSe₄, was successfully designed and synthesized by replacing sulfur with selenium based on SrZnGeS₄. Compared with the previously reported SrZnGeS₄ that suffers from both limited IR cutoff edge (23.6 μm) and second harmonic generation (SHG) response (0.9 × AgGaS₂), SrZnGeSe₄ fabricated in this work exhibits a larger IR cutoff edge (31.25 μm) as well as a stronger SHG response (4.7 × AgGaS₂). Meanwhile, SrZnGeSe₄ not only exhibits a larger SHG response (1.05 × AgGaSe₂) than commercial NLO compound AgGaSe₂, but also has a wider band gap (1.92 eV), higher laser-induced damage thresholds (5.0 × AgGaSe₂) and can achieve phase matching. First-principles calculations elucidate the crucial role of [ZnSe₄] and [GeSe₄] groups in enhancing the SHG response. These properties indicate that SrZnGeSe₄ is a promising candidate for IR NLO optical materials.