Anomalous photoluminescence enhancement due to hot electron transfer in core-shell Au-CdS nanocrystals

At room temperature, an enhanced photoluminescence (PL) intensity of core-shell Au-CdS nanocrystals (NCs) with respect to that of CdS NCs is observed; that is weakly affected at low temperature. PL intensity as a function of temperature depicts three different regions in CdS and Au-CdS NCs; the difference in the nature of curves implicates hot electron transfer from Au to CdS. Even though, the Fermi level of Au is at lower energy than conduction level of CdS NCs, plasmon induced charge transfer from Au to CdS overcomes the potential barrier that enhances band edge emission intensity at room temperature. Moreover, at lower temperature, PL emission splits in narrow and sharp distinct features from free exciton and bound exciton levels along with the first and second order phonon replica. In case of core-shell Au-CdS NCs, emission from free exciton and bound exciton remains unaffected, while phonon replica are perturbed; measured energy values of narrow lines fit well with the empirical Varshni equation revealing an intrinsic nature of CdS. The present work demonstrates decay of plasmon by generating electron in semiconductor; the concept with great potential for energy harvesting.