Photophysics of size-selected InP nanocrystals: Exciton recombination kinetics

We report here on the size-dependent kinetics of exciton recombination in a III-V quantum dot system, InP. The measurements reported include various frequency dependent quantum yields as a function of temperature, frequency dependent luminescence decay curves, and time-gated emission spectra. This data is fit to a three-state quantum model which has been previously utilized to explain photophysical phenomena in II-VI quantum dots. The initial photoexcitation is assumed to place an electron in a (delocalized) bulk conduction band state. Activation barriers for trapping and detrapping of the electron to surface states, as well as activation barriers for surface-state radiationless relaxation processes are measured as a function of particle size. The energy barrier to detrapping is found to be the major factor limiting room temperature band-edge luminescence. This barrier increases with decreasing particle size. For 30 Angstrom particles, this barrier is found to be greater than 6 kT/mol-a barrier which is more than an order of magnitude larger than that previously found for 32 Angstrom CdS nanocrystals. (C) 1996 American Institute of Physics.