Luminescence quantum yield and recombination constants in colloidal core/shell Ag$_{2}$S/ZnS and Ag$_{2}$S/SiO$_{2}$ quantum dots

The luminescence properties of colloidal Ag$_{2}$S quantum dots (QDs) with ZnS or SiO$_2$ shells coated with thioglycolic or 2-mercaptopropionic acids are comparatively analyzed. It is demonstrated that the quantum yield of the IR recombination luminescence of colloidal Ag$_2$S QDs increases by a factor of up to 35 as a result of formation of ZnS or SiO$_2$ shells with a simultaneous increase in the average luminescence lifetime. It is shown that the radiative and nonradiative recombination constants for core/shell Ag$_{2}$S/ZnS QDs coated with thioglycolic acid decrease, which is explained by localization of electrons in the shell and localization of holes in the core. In core/shell Ag$_{2}$S/SiO$_{2}$ QDs coated with 2-mercaptopropionic acid, the radiative recombination constant increases and the nonradiative recombination constant decreases. In this case, the increase in the radiative recombination constant is caused by localization of electrons and holes in the core. The decrease in the nonradiative recombination constant is explained by passivation of interface defects of QDs upon the shell formation.