The role of donor–acceptor defect complexes in the recombination of non-equilibrium carriers in cadmium iodide

This work presents optical, electrical, and calorimetric studies, which demonstrate that point defects in layered CdI2 crystals associate into bound centers, thereby altering the material’s properties. Such defective donordonor–acceptoracceptor pairs, and especially donor–acceptor–donor trimers, play a central role in the photophysics of cadmium iodide. These defective donor–acceptor pairs act as effective traps, extending the lifetime of charge carriers, and as radiative centers that provide strong luminescence through the efficient radiative recombination of geminated pairs (created by the same photon): excitons and photogenerated electron-hole pairs.