Optical and structural properties of ensembles of colloidal Ag$_2$S quantum dots in gelatin

The size dependences of the absorption and luminescence spectra of ensembles of hydrophilic colloidal Ag$_2$S quantum dots produced by the sol-gel method and dispersed in gelatin are analyzed. By X-ray diffraction analysis and transmission electron microscopy, the formation of core/shell nanoparticles is detected. The characteristic feature of the nanoparticles is the formation of crystalline cores, 1.5–2.0 nm in dimensions, and shells of gelatin and its complexes with the components of synthesis. The observed slight size dependence of the position of infrared photoluminescence bands (in the range 1000–1400 nm) in the ensembles of hydrophilic colloidal Ag$_2$S quantum dots is explained within the context of the model of the radiative recombination of electrons localized at structural and impurity defects with free holes.