Photodarkening and anti-Stokes photoluminescence from PbSe and Sr2+-doped PbSe quantum dots in silicate glasses

Photoluminescence (PL) properties of PbSe and Sr²⁺-doped PbSe quantum dots (QDs) doped in silicate glasses were investigated by changing the excited laser wavelength and intensity. When BaO was replaced by SrO, the Sr²⁺-doped PbSe QDs formed and showed large blue-shifts in both absorption and PL bands compared to the PbSe QDs. It is attributed to the increasing in band gap resulted by the incorporation of Sr²⁺ ions into PbSe QDs. These two kinds of QDs were excited by the laser with the wavelengths of 1319 and 1532 nm. When rising the pumping intensity up to 1000 mW, the PL intensity from Sr²⁺-doped PbSe QDs monotonically increased, while, the PL intensity from PbSe QDs reached maximum at pumping intensity at ~200 mW (λ_ex = 1319 nm) and ~300 mW (λ_ex = 1532 nm). The good resistance to photodarkening of Sr²⁺-doped PbSe QDs is indicated passivation effect on the surface defects from Sr²⁺ ions doping. For Sr²⁺-doped PbSe QDs the anti-Stokes photoluminescence (ASPL) were observed when using both 1319 and 1532 nm excitation. The integrated intensity of the ASPL is linear with the excitation intensity, which indicates that the ASPL belongs to the phonon-assisted one-photon process. And the ASPL intensity as a function of excitation intensity shows a size dependence of the QDs.