The temperature dependence of the absorption and fluorescence spectra of colloidal CdSe nanocrystals was compared for three different shapes (dots, rods, and tetrapods) in the range of 4–300K. While the shift of the fluorescence maximum indicates little dependence on the shape, the authors find that the broadening of the emission spectrum behaves very differently for dots and rods, indicating major differences in the broadening mechanisms for different shapes. Tetrapods behave more similarly to dots, which suggests that the lowest exciton state is centered at the core.

We show a femtosecond fluorescence upconversion setup with broadband detection to measure time-resolved emission spectra in the $300–550\mathrm{nm}$ range, upon excitation between 250 and $300\mathrm{nm}$, with a time resolution of $100\mathrm{fs}$. We present time-resolved fluorescence emission spectra of 2,5-diphenyloxazole in solution, which demonstrate the capabilities of the setup.

We report on the (sub)picosecond relaxation processes in PbSe quantum dots of different sizes, measured by a near-infrared photoluminescence upconversion technique. The early-time spectra are characterized by emission from several low-lying excited states. The direct measurement of the Huang-Rhys factors of the lowest excited states excludes strong electron-phonon coupling in the intraband relaxation. The kinetics point to a fast sequential cascade process between excited states, governed by energy gaps and a quasicontinuous valence-band structure.