Delayed electron relaxation in CdTe nanorods studied by spectral analysis of the ultrafast transient absorption

- We study the photophysics of CdTe nanorods by ultrafast absorption spectroscopy.
- We fit photobleaching and photoinduced absorption features at all time delays.
- Dynamics are extracted from superpositions of bleaches (Gaussians) and derivatives.
- Fast non-radiative recombination and slower hole trapping processes are extracted.
- A potential approach to unveil ultrafast non-radiative recombination processes.

In transient absorption (TA) spectra, the bleach features originating from state filling are overlapped by their energy-shifted derivatives, arising from excited state energy level shifts. This makes the direct extraction of carrier dynamics from a single-wavelength time-trace misleading. Fitting TA spectra in time, as Gaussian functions and their derivative-like shifted Gaussians, allows to individually extract the real dynamics of both photobleached transitions, and their energy shifts. In CdTe nanorods (NRs) we found a delayed heating of holes due to the release of the large excess energy in the electron relaxation process. The slow hole-trapping process is consistent with a high number of surface trap states in these model NRs. Our results show that only a correct disentanglement of bleaching and energy shift contributions provides a reliable framework to extract the underlying carrier relaxation dynamics, including trapping, non-radiative recombination, and eventually carrier multiplication.