We observe ultrafast 1P-to-1S intraband relaxation in PbSe and CdSe nanocrystals (NCs) that have distinct energy spectra. While ultrafast dynamics in CdSe NCs has typically been interpreted in terms of electron-hole energy transfer, this mechanism is not active in PbSe NCs because of sparse densities of states in the conduction and valence bands. Our observations of temperature activation and confinement-enhanced relaxation in PbSe NCs can be explained by efficient multiphonon emission triggered by nonadiabatic electron-phonon interactions and are indicative of large, size-dependent, intraband Huang-Rhys parameters.

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We demonstrate the optical orientation and alignment of excitons in a two-dimensional layer of CsPbI3 perovskite nanocrystals prepared by colloidal synthesis and measure the anisotropic exchange splitting of exciton levels in the nanocrystals. From the experimental data at low temperature (2 K), we obtain the average value of anisotropic splitting of bright exciton states of the order of 120 µeV. Our calculations demonstrate that there is a significant contribution to the splitting due to the nanocrystal shape anisotropy for all inorganic perovskite nanocrystrals.