Size-dependent photoluminescence of PbS QDs embedded in silicate glasses

PbS quantum dots (QDs) with a mean radii of 1.27 nm to 7.32 nm were precipitated in alkaline-earth silicate glasses enriched in sulfur. A transmission electron microscope image and absorption spectra evidenced the narrow size dispersion of PbS QDs and discrete energy levels of PbS QDs. Upon above-band-gap excitation, symmetry of the photoluminescence from PbS QDs was strongly dependent on their size. Photoluminescence from small PbS QDs showed a long-wavelength tail and vice versa for large PbS QDs. The size dependence of full width at half maximum, PL energy and Stokes shift on the size of PbS QDs suggested that the electron/hole trap states of PbS QDs and the defects states on the interface between PbS QDs and glass matrix have great effect on the photoluminescence properties of PbS QDs.