Framework for Extracting the Rates of Photophysical Processes from Biexponentially Decaying Photon Emission Data

There is strong interest in designing and realizing optically
active
semiconductor nanostructures of greater complexity for applications
in fields ranging from biomedical engineering to quantum computing.
While these increasingly complex nanostructures can implement progressively
sophisticated optical functions, the presence of more material constituents
and interfaces also leads to increasingly complex exciton dynamics.
In particular, the rates of carrier trapping and detrapping in complex
heterostructures are critically important for advanced optical functionality,
but they can rarely be directly measured. In this work, we develop
a model that includes the trapping and release of carriers by optically
inactive states. The model explains the widely observed biexponential
decay of the photoluminescence signal from neutral excitons in low-dimensional
semiconductor emitters. The model also allows determination of likelihood
intervals for all of the transition rates involved in the emission
dynamics, without the use of approximations. Furthermore, in cases
for which the high-temperature limit is suitable, the model leads
to specific values of such rates, outperforming the reduced models
previously used to estimate those quantities. We demonstrate the value
of this model by applying it to time-resolved photoluminescence measurements
of CdSeTe/CdS heterostructures. We obtain values not only for the
radiative and nonradiative lifetimes but also for the delayed photoluminescence
originating in trapping and release.