The size dependence recombination luminescence of hydrophilic colloidal CdS quantum dots in gelatin

The recombination photoluminescence (PL) properties of hydrophilic colloidal CdS quantum dots (QDs) dispersed in gelatin were investigated. The average size of QDs varies from 2.4 to 4.4 nm. The size dependence of the emission peak position is defined in the range from 1.65 to 2.27 eV. The PL decay (0.3-4·103 ns) is accompanied by the red shift of its maximum. It is interpreted as the radiative recombination via the donor-acceptor pairs. The analysis of the half-width and shape of the observed PL spectra was performed taking into account the QDs size distribution and the Coulomb interaction of donor and acceptor uniformly distributed in QD volume. The deviation of the theoretical PL spectra from experimental data on the half-width was determined, which amounted of the order 0.4 eV. It is concluded that to describe the PL spectra of CdS QDs it is necessary to consider a different degree of localization of the wave functions and the variation of the binding energy of the donor and acceptor versus their depth in the QD volume.