Temporal evolution of radiative rate reveals the localization of holes in CuInS2-based quantum dots

The collapse of carriers into polarons strongly impacts properties such as charge transport, separation and recombination that are of fundamental relevance to opto-electronic devices such as photovoltaics. Here we observe the real-time process of the collapse of a wavefunction using ultrafast spectroscopy. We develop a method to extract changes in spontaneous lifetimes of an emitter over the course of its emission lifetime. This method enables us to detect the wavefunction collapse of photogenerated holes in quantum dots (QDs) . In particular, we observe that the spontaneous emission lifetime of these QDs is ~46 ns immediately after excitonic cooling but changes drastically to ~294 ns over the first 15 ps. The evolution in emission lifetimes and the corresponding variation in emission energetics imply changes in the hole wavefunction even after usual excitonic cooling is complete, and is consistent in its migration into a phonon coupled state located within the semiconductor band gap.