PbSe nanocrystal colloids exhibit a well-defined excitonic structure with the lowest energy exciton tuning from 0.5 to 1 eV, as a function of size. Band-edge fluorescence is observed from 1.2 to 2 μm with a small Stokes shift, sub-μs lifetime, and near-unity quantum yield. Upon pumping at 1.064 μm, the first exciton decay is consistent with radiative relaxation at low pump intensity and with Auger recombination at higher pump intensities. Optically induced absorption is observed at approximately midgap. These transitions exhibit strengths similar to the interband exciton and are size-tunable. They are assigned to the 1Se,h−1Pe,h and 1Pe,h−1De,h intraband excitations. Intraband pump−probe measurements of the 1Se,h−1Pe,h transition reveal a short lifetime and the absence of the phonon bottleneck.

Interband and Intraband Optical Studies of PbSe Colloidal Quantum Dots

Semiconductor superlattices: a model system for nonlinear transport

Fluorescence and phosphorescence from higher excited states of organic molecules.

We report the first experimental observation of a striking convergence of Auger recombination rates in nanocrystals of both direct- (InAs, PbSe, CdSe) and indirect-gap (Ge) semiconductors, which is in contrast to a dramatic difference (by up to 4-5 orders of magnitude) in the Auger decay rates in respective bulk solids. To rationalize this finding, we invoke the effect of confinement-induced mixing between states with different translational momenta, which diminishes the impact of the bulk-semiconductor band structure on multiexciton interactions in nanocrystalline materials.

Universal size-dependent trend in auger recombination in direct-gap and indirect-gap semiconductor nanocrystals.

This research is supported in part by the Australian Research
Council, Australia, Institute of Physical and Chemical
Research RIKEN, and the Ministry of Education, Science,
Sports and Culture, Japan.

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Review of zincblende ZnO: Stability of metastable ZnO phases

Third‐order optical nonlinearities and recombination processes of photoexcited electron‐hole plasma in PbSe and PbTe are directly monitored by picosecond pump‐probe experiments in the wavelength range from 3 to 10 μm. After excitation, a strong blue shift of the absorption edge and large changes of the refractive index are found. Time‐resolved studies of the absorption changes at lattice temperatures between 70 and 160 K reveal a fast partial decrease of the carrier density within 100 ps at excitation densities exceeding 7×1017 cm−3. Comparative emission spectra demonstrate that this behavior is due to recombination by stimulated emission. At room temperature the nonradiative Auger recombination dominates on a 0.5–2 ns time scale below the threshold of stimulated emission. The overall Auger coefficients for carrier densities of about 1018 cm−3 are derived from the data and have values of cAPbSe=1.1±0.3×10−28 cm6/s and cAPbTe=2.5±1.3×10−28 cm6/s.

Fast recombination processes in lead chalcogenide semiconductors studied via transient optical nonlinearities

Recombination dynamics in GaN

We investigate the transient surface emission and the optical gain of cubic GaN on GaAs(001) upon pulsed optical pumping at room temperature. The initial decay time of the transient surface emission drastically decreases with increasing excitation density, reaching a value as short as 20 ps at a fluence of 50 μJ cm−2. This rapid decay suggests the presence of laterally amplified spontaneous emission. In fact, gain-stripe measurements of the edge emission reveal an optical gain exceeding 100 cm−1 at a fluence of 20 μJ cm−2.

R. Klann

Papers

Fast recombination processes in lead chalcogenide semiconductors studied via transient optical nonlinearities

Recombination dynamics in GaN

Optical gain in optically pumped cubic GaN at room temperature

Transition between synchronization and chaos in doped GaAs/AlAs superlattices

Radiationless processes in antiaromatic molecules: The photophysics of s-indacene studied by ultrashort light pulses