Excitation and Emission Dynamics in Individual Semiconducting Nanocrystals: Bright dots, better future

Abstract

Quantum dots are e cient luminescent materials with a high absorbance in the blue regime while also displaying narrow emission wavelengths. Quantum dots are interesting to study with the aim to improve their optical properties by nanocrystal engineering. Characteristic properties of these materials include the non-constant emission intensity and the non-stable center emission wavelength. These features are not readily visible on the ensemble level, which therefore requires advanced optical set-ups to study these features for single particles. While most studies focused on characterizing the time-resolved emission features, studies focusing on the excitation spectra have been performed much less. In this work, the emission and excitation spectra over time were measured simultaneously. It was also observed that the quantum dot had a pronounced non-constant emission intensity over the course of the experiment, which allowed identifying di erent states based on intensity thresholding. It was observed that the quantum dot exhibited di erences in the photoluminescence excitation spectra amongst the individually assigned states. This indicated that multiple decay mechanisms were observed in a single quantum dot. Moreover, a qualitatively similar energy di erence for the di erent absorption transitions compared to the band-edge emission was for the highest-intensity state. Furthermore, no such similarity was observed between the di erent states. These results are an important step towards a more complete understanding of the physical processes that occur in these materials.