An illuminating framework:: Understanding the photoluminescence of α-CuAlCl4

CuAlCl4 exemplifies a new class of phosphors based on metal halide analogues of aluminophosphates. The alpha- and beta-CuAlCl4 phases show brilliant blue to blue-green luminescence. The electronic structure of the CuAlCl4 corner sharing tetrahedral frameworks has been explored by fluorimetric and diffuse reflectance measurements on the isomorphous series alpha-CuAlBrxCl4-x (x = 0-4). The photoluminescence is demonstrated to be a bulk property of the electronically isolated CuCl4/2 tetrahedra within the framework matrix. Remarkably, the structural framework is flexible such that at least 1 mol of small molecule gases per CuAlCl4 formula unit can be reversibly sorbed. The sorption/desorption of small molecule gases further results in the reversible quenching of the photoluminescence.