Features of the dynamics of the photoluminescence spectrum of the Cu$_3$In$_5$S$_9$ crystal with a change in the laser excitation intensity

Photoluminescence spectra were studied on a naturally formed surface of a layered Cu$_3$In$_5$S$_9$ crystal upon excitation by nanosecond laser radiation. At relatively low levels of optical excitation intensity, luminescence quenching was observed near a photon energy of 1.636 eV in a narrow energy band near 118 meV. This phenomenon is explained by the formation of bound triplet excitons and their dissociation with the emission of phonons. It is shown that, as the intensity of the optical excitation of the crystal increases, the impurity emission band in the crystal disappears. The photocurrent spectrum of Cu$_3$In$_5$S$_9$ at 295 K is formed by peaks at energies of 1.53 and 1.81 eV. The lifetime of nonequilibrium electrons through fast centers is 20 ns. From the temperature dependence of the electrical conductivity of the Cu$_3$In$_5$S$_9$ crystal in the range 110–350 K, the activation energies of two donor levels, 0.28 and 0.76 eV, were determined.