Polarised Photoluminescence from Surface-Passivated PbS Nanocrystals

Effective surface-passivation of PbS nanocrystals in aqueous colloidal solution has been achieved following treatment with CdS precursors. The resultant photoluminescent emission displays two distinct components, one originating from the absorption band-edge and the other from above the absorption band-edge. We show that both of these components are strongly polarised but display distinctly different behaviours. The polarisation arising from the band-edge shows little dependence on the excitation energy while the polarisation of the above-band-edge component is strongly dependent on the excitation energy. In addition, time resolved polarisation spectroscopy reveals that the above-band-edge polarisation is restricted to the first couple of nanoseconds, while the band-edge polarisation is nearly constant over hundreds of nanoseconds. We recognise an incompatibility between the two different polarisation behaviours, which enables us to identify two distinct types of surface-passivated PbS nanocrystal.Comment: Preprint, 19 pages, 4 figure

Fluorophosphate glasses doped with PbSe quantum dots and their nonlinear optical characteristics

A new fluorophosphate glass matrix containing PbSe quantum dots characterized by a narrow size distribution (Delta R/R similar to 5-7%, where R is the size of a quantum dot) is prepared under heat treatment. It is demonstrated that fluorophosphate glasses can be doped by introducing (ZnSe + PbO) or PbSe into the composition of the glass. The optical absorption spectra of the quantum dots corresponding to the strong quantum confinement regime are studied over a wide range of quantum-dot sizes (4-18 nm). The nonlinear optical absorption is investigated at a wavelength of 1.54 mu m. It is revealed that the introduction of (ZnSe + PbO) rather than of PbSe into the composition of the glass improves the bleaching contrast owing to a more uniform distribution of the quantum dots over the volume of the glass sample