Excitation-wavelength- and size-dependent photo-darkening and photo-brightening of photoluminescence from PbS quantum dots in glasses

Abstract

PbS quantum dots (QDs) with mean radii of 3.7 nm to 9.0 nm are precipitated in silicate glasses. Upon above-band-gap excitation, photoluminescence from QDs is strongly dependent on their size and excitation wavelength, exhibiting photo-darkening (PD) or photo-brightening (PB). Photoluminescence of PbS QDs exhibits strong darkening by short excitation wavelength but the darkening gradually mitigated as the excitation wavelength increased and even turns to be photo-brightening at room temperature. But PD and PB show a much more complicated variation tendency under the same excitation condition when the size of QDs increased. The dependence of PD and PB on the QDs’ size and excitation wavelength indicates that electron/hole trap states of PbS QDs, defect states in surrounding glass matrix as well as on the interface between the glass matrix and PbS QDs all have strong effects on the photoluminescence properties of PbS QDs. These findings are important to modulate the photoluminescence and promote the potential applications of PbS QDs embedded glasses towards various optoelectronic devices.