Investigations of temperature-dependent photoluminescence of uncoated and silver-coated CdS quantum dots

We report temperature-dependent photoluminescence (PL) studies and PL relaxation dynamics for uncoated and silver-coated CdS quantum dots (QDs). Room-temperature photoluminescence studies indicate that the presence of silver coating on CdS QD samples enhances the blue luminescence corresponding to the band-to-band transitions by a factor of ten compared to the uncoated samples. Furthermore, the decay time measurements using Time Correlated Single Photon Counting technique demonstrate F\"{o}rster resonance energy transfer (FRET) between silver-shell and CdS-core in silver-coated CdS QD samples. A detailed investigation of temperature-dependent PL spectra of uncoated CdS QD samples reveals the role of thermally-activated surface-trap states, exciton-LO phonon coupling and ionized impurity scattering. In case of silver-coated QDs, the temperature-dependent PL peak energy corresponding to the band-to-band transitions presents a consecutive red-blue-red shift (S-shaped) behavior. Whereas, the full width at half maximum (FWHM) shows a successive blue-red-blue shift (inverted S-shaped) characteristic with increasing temperature.