Ca2La(MS4)(BS3) (M = Ge/Si and Sn/Si): High performance infrared nonlinear optical materials designed by atomic site co-occupancy strategy

Abstract

Exploration of new material systems and optical performance enhancement are huge challenges during the study of infrared nonlinear optical (IR NLO) materials. In this work, the first thioborate-thiogermanate and thioborate-thiostannate, Ca2La(Ge0.72Si0.28S4)(BS3) and Ca2La(Sn0.75Si0.25S4)(BS3), containing both co-occupied Ca2+/La3+ cation and [Ge/SiS4]4- or [Sn/SiS4]4-anion sites, have been designed through an atomic site co-occupancy strategy. They inherited favourable 3D network structures in which the effectively aligned [MS4]4- and [BS3]3- functional anions are bridged by Ca2+/La3+ cations. Remarkably, the title compounds achieved excellent IR NLO properties, including good chemical and thermal stabilities, wide light transmission ranges (0.45-11 μm), strong second harmonic generation responses (1.5 and 2.0 times that of commercial AgGaS2 at 2.05 µm) and high laser induced damage thresholds (7 and 6 times that of AgGaS2). Theoretical calculation and experimental results revealed that, on the basis of excellent structural framework, introducing more active functional groups through atomic site co-occupancy can simultaneously enhance the second harmonic generation effect and maintain a relatively high laser induced damage threshold. This work not only offers an easier synthetic route for mixed anionic thioborates, but also provides inspiration for the design of well-performed NLO materials.