Hot excitons and exciton excitation spectra

Tailoring the Spectroscopic Properties of Semiconductor Nanowires via Surface-Plasmon-Based Optical Engineering

“… 86 Upon addition of a conformal metal shell, there is an increase in the overall photoluminescence intensity (after taking into account in- and out-coupling efficiencies). 26 Interestingly, the spectral shape now features sharp peaks at multiples of the LO phonon energy in CdS (∼38 meV 87 ) from the laser excitation energy above the band edge, which suggests that LO phonon scattering now serves to both mediate carrier relaxation and also scatter the carrier back to the light line (Figure 3 a, green curve), leading to emission from unthermalized (hot) charge carriers. However, the most interesting thing is that in a steady-state spectrum, emission from states that are very short lived (on the order of the exciton–LO phonon interaction time scale, i.e., a few ps) is observable, which strongly suggests that the radiative lifetime of the cavity is becoming comparable to the LO phonon interaction time scales due to the Purcell effect.…”