Spectral red shift in the Ag ²⁺ doped CdS quantum dots

Photoluminescence spectrum of pure and Silver (Ag ²⁺) doped cadmium sulfide (CdS) quantum dots with different doping concentrations and pure Cd concentrations were carried out. A systematic red shift in the band gap energy, ranging from 2.48 eV to 2 eV was noticed with the increasing Ag ²⁺ concentration, however, no shift in the band gap energy was observed for varying pure Cd concentration. The red shift of the band gap energy was consistent in both photoluminescence and absorption spectra and the observed energy shifts are equal to the fundamental and overtone energies of the longitudinal optical phonon of Cd ²⁺S.