We have analyzed the possibilities of using the phenomenon of photostimulated luminescence flash for optical diagnosing of energy levels of structural and impurity defects of semiconductor crystals and nanostructures. New data on the spectra of deep localized states associated with adsorbed few-atom clusters Zn on the surface of ZnS; clusters Cd, Cu, and Ag on the surface of CdS; and clusters Ag on the surface of AgBr(I) have been presented, as well as results of investigation of photostimulated assembling processes of few-atom clusters on the surface of crystals using this phenomenon. We are the first to show the potential of the luminescence flash technique for studying the mutual arrangement of the levels of dye molecules and the bands of the crystal on the surface of which they are adsorbed, as well as of the spectra of localized states in colloidal CdS semiconductor quantum dots.