We present the structural and optical characterization of colloidal PbSe nanocrystals. The lowest-energy exciton transitions in these structures, with diameters between 3 and 8 nm, occur at wavelengths between 1.0 and 1.85 µm. Band-edge luminescence spectra with quantum yields as high as 80% are observed. Unexpectedly long (∼300 ns) luminescence lifetimes are observed. These properties are promising for applications in optoelectronics and microscopy.

Resonant nonradiative energy transfer between close-packed PbS quantum dots is observed in continuous-wave and time-resolved fluorescence experiments. Samples of nominally a single dot size, and two dot sizes, were investigated. In both cases, the time-integrated fluorescence exhibits a substantial redshift compared to the emission from dots in solution, and energy transfer can be observed directly in spectrally resolved fluorescence transients.

We have synthesized a series of chalcogenide glasses from the As-S-Se system that is designed to have strong nonlinearities. Measurements reveal that many of these glasses offer optical Kerr nonlinearities greater than 400 times that of fused silica at 1.25 and 1.55mum and figures of merit for all-optical switching greater than 5 at 1.55mum .

The relaxation of strongly-confined electrons and holes between 1P and 1S levels in colloidal PbSe nanocrystals has been time-resolved using femtosecond transient absorption spectroscopy. In contrast to II-VI and III-V semiconductor nanocrystals, both electrons and holes are strongly confined in PbSe nanocrystals. Despite the large electron and hole energy level spacings (at least 12 times the optical phonon energy), we consistently observe picosecond time-scale relaxation. Existing theories of carrier relaxation cannot account for these experimental results. Mechanisms that could possibly circumvent the phonon bottleneck in IV-VI quantum dots are discussed.