Near-infrared photoluminescence from molecular crystals containing tellurium

Abstract

We report the observation of near-infrared photoluminescence from Te₄(Ga₂Cl₇)₂ and Te₄(Al₂Cl₇)₂ molecular crystals containing Te₄²⁺ polycations. The experimental and theoretical results clearly revealed that the Te₄²⁺ polycation is a smart near-infrared emitter with characteristic emission peaks at 1252 and 1258 nm for Te₄(Ga₂Cl₇)₂ and Te₄(Al₂Cl₇)₂ crystals, respectively, resulting from the intrinsic electronic transitions of Te₄²⁺. Furthermore, it was also found that the emissions strongly depend on the excitation wavelengths for both Te₄(Ga₂Cl₇)₂ and Te₄(Al₂Cl₇)₂ samples, most possibly due to the co-existence of other Te-related optically active centers. This research not only enriches the species of luminescent charged p-block element polyhedra and deepens the understanding of Te-related photophysical behaviors, but also may stimulate efforts for designing novel material systems using such active centers. It is also greatly expected that these sub-nanometer optically active species could exist in other systems such as glasses, polymers, and bulk optical crystals, and the stabilization of these centers in widely used hosts will pave the way for their practical applications.