Impact of Photo-induced Physical and Chemical Processes on Lateral Transport of Excitons in Quantum Dot Thin Films

Abstract

We study how lateral transport of excitons (exciton diffusion) in quantum dot thin films is influenced by the photo-physical and photo-chemical properties of the quantum dots. For this, thin layers of colloidal quantum dots on glass substrates are exposed to laser pulses with different total average powers. Spatial mappings of the lifetimes of the quantum dots within the diffraction-limited spot sizes of the laser beam show that their photo-induced properties can be influenced by the excitation intensity mode profiles significantly, leading to three distinct regimes of exciton diffusion across the films. These include the cases wherein the lateral energy transport (i) is linearly influenced by the laser intensity mode profiles, (ii) is convoluted by variations of laser intensity and photo-physical and photo-chemical properties of the quantum dots, and (iii) is significantly influenced by the formation of oxidation hole burning. The third regime, oxidation hole burning effect, occurs at the center of the excited regions of the quantum dot thin films, suppressing their emission and transport of energy considerably. We will discuss variations of the diffusivity as a function of the laser intensity mode profiles and time. The results shed light on the impact of photo-chemical and photo-physical processes on transport of energy in quantum dot thin films, highlight the regimes of efficient exciton diffusion, and demonstrate the prominent impact of the intensity mode profiles of the light used to excite quantum dot thin films.