Luminescence properties of Cr:ZnSe: Comparison between a single crystal and a film deposited by RF magnetron co-sputtering

We investigated the optical properties of a Cr²⁺:ZnSe film deposited by radiofrequency magnetron co-sputtering and compared them with those of a single crystal. The mid-infrared room temperature photoluminescence spectra under direct (1850 nm) and indirect (458 nm) excitation revealed that chromium has been incorporated in the Cr²⁺ active state. The difference of Cr²⁺ fluorescence lifetime values (measured between 10 and 400 K) between both samples was attributed to the presence in the film of firstly a large amount of chromium in a valence state different from the Cr²⁺ active state and secondly structural defects in the ZnSe host matrix. Visible photoluminescence measurements were carried out in order to identify these structural defects.