Optical properties of Ce3+ and Tb3+ co-doped ZnS quantum dots

Ce3+ and Tb3+ co-doped ZnS quantum dots (QDs) were synthesized using a facile and effective wet chemical method. The effect of Tb3+ concentration on the structure and optical properties of the co-doped QDs was explored thoroughly using various characterization methods. The chemical composition and oxidation state of the elements in the synthesized QDs were examined by X-ray photoelectron spectroscopy (XPS). The crystal structure and luminescence properties of the synthesized QDs were investigated using X-ray diffraction (XRD) and photoluminescence (PL). The change in the crystal structure of the Ce3+ and Tb3+ co-doped QDs with an increase in the concentration of Tb3+ dopant from 1% to 8% was observed for the first time. The excitation spectra of Ce3+ and Tb3+ co-doped QDs were investigated using the photoluminescence excitation (PLE) technique. The energy transfer (ET) from Ce3+ to Tb3+ ions in the ZnS host lattice occurred effectively because of the large spectral overlap between the emission band of Ce3+ and the excitation band of Tb3+ ions. The observed properties revealed that doping with Ce3+ enhanced the energy transfer process and the interaction mechanism in energy transfer was dominated by dipole-dipole interaction. The thermal stability of the co-doped QDs was explored by studying their PL spectra in the temperature range of 15–300 K. Ce3+ and Tb3+ co-doped ZnS QDs exhibited a very long decay time on the order of ms. The valuable optical properties of Ce3+ and Tb3+ co-doped ZnS QDs make them potentially useful for photovoltaic, photocatalyst, and biosensing applications.