Applying Marcus Theory to Describe Photoluminescent Intermittency and Temperature-Dependent Emission in CdTe Nanoplatelets

Photoluminescence (PL) intermittency (also known as blinking) is a critical aspect of the optical properties of molecules and nanomaterials. Considerable work has expounded on the mechanism of blinking in nanocrystals, with the canonical model arguing that intermittently trapped charges serve to quench emission via charge-exciton Auger recombination. The dynamics of the emission trace are analyzed by fitting a histogram of on- and off-times to power-law distributions. These histograms in turn reveal nonexponential kinetics, arguing for a distribution of electron or hole traps. What is not revealed is the origin of these distributed states, whether they arise from various trap energetic depths, long-range electron or hole tunneling, or any other process that gives rise to distributions of rates. We explore a model that invokes both a distribution of trap energies, combined with the chemical intuition of charge transfer via Marcus theory. We find that a self-consistent Marcus theory model can explain different power-law slopes for on- and off-times and the observed changes in intensity as a function of temperature in films of CdTe nanoplatelets (NPLs). We believe this provides a self-consistent model to describe blinking behavior that leads to unusually low PL quantum yield (QY) in CdTe NPLs, and it argues that improved passivation will be critical to achieving higher QY.