Kinetics of luminescence decay of nanocrystals: physical models and approximation by a sum of three exponential functions

The measurement of the kinetics of luminescence decay of nanocrystals (NCs) – quantum dots (QDs), nanowires, nanoplates and quantum rings – is an important tool for studying the photodynamics of their excited states, that allows identifying the type and number of traps for charge carriers (electrons, holes) or acceptors of excitation energy (molecules, other QDs) located on the surface or near the NCs, as well as to estimate the energy of traps and to determine the mechanism of transfer of the energy of electronic excitation from the NCs to acceptors. Usually, the kinetics of luminescence decay is approximated by a sum of two or three exponential functions. In this case, the fitting parameters are the amplitudes and decay times of the exponential components. This paper analyzes the experimental conditions under which such an approximation has a clear physical meaning (long-range nonradiative energy transfer, contact quenching of luminescence, reversible trapping of charge carriers), and establishes a relationship between the fitting parameters.