A Promising Mid-Infrared Nonlinear Optical Crystal with Well-balanced Properties

Abstract

The Nonlinear optical (NLO) crystals have attracted significant interest for their ability to extend the frequency of lasers. Here, we report a new germanate NLO crystal, PbZnGeO4 (PZGO), which features a unique 3D framework built from asymmetric ZnO4, GeO4, PbO3, and PbO4 units. PZGO exhibits a short UV cutoff edge of 300 nm, corresponding to a large bandgap of 3.7 eV, and a broad transparent range extending up to 5.9 μm, effectively covering the crucial atmospheric transmission window of 3-5 μm. Notably, it achieves a strong phase-matchable second-harmonic generation (SHG) intensity (2.5×KDP), along with a suitable birefringence of 0.04 at 1064 nm, superior to most reported germanate NLO crystals. First-principles calculations reveal that optical activities of PZGO primarily originates from the highly distorted Pb-O units with stereochemically lone-pair electrons.