Temperature effects and mechanism of IR luminescence of colloidal Ag2Se QDs passivated with 2-mercaptopropionic acid

The paper presents the new luminescence regularities of hydrophilic colloidal Ag2Se quantum dots (QDs), passivated with 2-mercaptopropionic acid molecules. It was found that an increase in the selenium precursor concentration, as well as a decrease in the sample temperature to 80 K provides the luminescence enhancement in the long-wavelength band (840-890 nm) with simultaneous strong quenching in the short-wavelength band (715-720 nm). The Stokes shift analysis suggested that the short-wavelength luminescence peak arises as a result of radiative annihilation of an exciton, while the long-wavelength one arises due to radiative recombination at trap states. An analysis of the luminescence excitation spectra at both luminescence bands, luminescence decay curves along the luminescence spectrum, and temperature dependence of the luminescence intensity made it possible to present a scheme of the energy levels and transitions that determine the luminescence regularities of colloidal Ag2Se QDs.