Simultaneous Electronic and Thermal Signatures in Pump-Probe Spectroscopy of Semiconductor Nanocrystal Films.

Abstract

Thermal contributions are typically ignored in optical spectroscopy of semiconductor nanomaterials. However, such considerations are important for an accurate interpretation of spectroscopy measurements. Here, we identify signatures of transient photoinduced heating in optical pump-probe signals of colloidal semiconductor nanocrystal films. We find that lattice heating following excitation above the bandgap or at high fluences leads to a significant temperature-induced transient signal that impacts three aspects of pump-probe measurements: the transient spectra, relaxation kinetics, and spatiotemporally resolved carrier diffusivity. The effects are general across nanocrystal core material, appearing in both CdSe and PbS quantum dot films. This study proposes several methods for distinguishing simultaneous electronic and thermal contributions to transient measurements as well as guidelines for how to avoid misassignments. On the other hand, we discuss the ability to track both electronic and thermal transport as a largely missed opportunity that can be leveraged.