An Illuminating Framework:  Understanding the Photoluminescence of α-CuAlCl₄

CuAlCl 4 exemplifies a new class of phosphors based on metal halide analogues of aluminophosphates. The α- and β-CuAlCl 4 phases show brilliant blue to blue-green luminescence. The electronic structure of the CuAlCl 4 corner sharing tetrahedral frameworks has been explored by fluorimetric and diffuse reflectance measurements on the isomorphous series α-CuAlBr x Cl 4 - x ( x = 0−4). The photoluminescence is demonstrated to be a bulk property of the electronically isolated CuCl 4/2 tetrahedra within the framework matrix. Remarkably, the structural framework is flexible such that at least 1 mol of small molecule gases per CuAlCl 4 formula unit can be reversibly sorbed. The sorption/desorption of small molecule gases further results in the reversible quenching of the photoluminescence.