Optical and energetic properties of the Tl$_{4}$CdI$_{6}$ crystal

The band spectrum and density of states of the Tl$_{4}$CdI$_{6}$ crystal have been investigated. Based on theoretical calculations, the electron and hole effective masses have been determined, the localization of the minimum band gap has been found, the origin of the conduction and valence bands has been established, and the nature of the direct-gap transition has been disclosed. Photoluminescence spectra and photoluminescence band excitation spectra at a temperature of 90 K have been experimentally detected. The identification and nature of the observed bands are discussed.