Bandgap Tuning in Molecular Alloy Crystals Formed by Weak Chalcogen Interactions.

Abstract

We demonstrate systematic tuning in the optical bandgaps of molecular crystals achieved by the generation of molecular alloys/solid solutions of a series of diphenyl dichalcogenides-characterized by weak chalcogen bonding interactions involving S, Se, and Te atoms. Despite the variety in chalcogen bonding interactions found in this series of dichalcogenide crystals, they show isostructural interaction topologies, enabling the formation of solid solutions. The alloy crystals exhibit Vegard's law-like trends of variation in their unit cell dimensions and a nonlinear trend for the variation in optical bandgaps with respect to their compositions. Energy-dispersive X-ray and spatially resolved Raman spectroscopic studies indicate significant homogeneity in the domain structure of the solid solutions. Quantum periodic calculations of the projected density of states provide insights into the bandgap tuning in terms of the mixing of states in the alloy crystal phases.