Regulating the key performance parameters for Hg-based IR NLO chalcogenides via bandgap engineering strategy

Abstract

Recently, non-centrosymmetric (NCS) Hg-based chalcogenides have garnered significant interest due to their strong second-harmonic-generation intensities (deff), making them attractive candidates for infrared nonlinear optical (IR-NLO) application. However, achieving both wide band gaps (Eg) and large phase-matched deff simultaneously in these materials remains a challenge due to their inherent constraints on each other. In this research, we have successfully obtained two quaternary NCS Hg-based chalcogenides, Rb2HgGe3S8 and Cs2HgGe3S8, by implementing a bandgap engineering strategy that involves alkali metal introduction and Hg/Ge ratio regulation. Both compounds consist of 2D [HgGe3S8]2– anionic layers made of 1D [HgGeS6]6– chains and dimeric [Ge2S6]4– polyhedra arranged alternately, and the charge-balanced Rb+/Cs+ cations located between these layers. Remarkably, Rb2HgGe3S8 and Cs2HgGe3S8 exhibit overall properties required for promising IR-NLO materials, including sufficient PM deff (0.55–0.70 × AgGaS2@2050 nm), large Eg (3.27–3.41 eV), giant laser-induced damage thresholds (17.4–19.7 × AgGaS2@1064 nm), broad optical transmission intervals (0.32–17.5 µm), and suitable theoretical birefringence (0.069–0.086@2050 nm). Furthermore, in-depth theoretical analysis reveals that the exceptional IR-NLO performance is attributed to the synergy effects of distorted [HgS4] and [GeS4] tetrahedra. Our study provides a useful strategy for enhancing the Eg and advancing Hg-based IR-NLO materials, which is expected to extended and implemented in other chalcogenide systems.