Optical properties and energy transfer mechanism of Eu3+, Ce3+ doped and co-doped ZnS quantum dots

Semiconductor ZnS quantum dots (QDs) co-doped with Eu3+ and Ce3+ were synthesized by the chemical method. The optical properties of the samples were characterized by absorption spectroscopy, photoluminescence (PL) spectroscopy and PL-decay lifetime. X-ray diffraction revealed that the QDs had a zincblende structure and a particle size of about 3 nm. The presence of Eu3+ and Ce3+ ions in the samples were proved by X-ray photoelectron spectroscopy. The properties of ligand field and the intensity parameters of Eu3+ doped ZnS QDs were analyzed by Judd-Ofelt theory. For Ce3+ and Eu3+ ions co-doped in ZnS QDs, the luminescence intensity and lifetime of the 5d1 (Ce3+) level decrease while the emission intensity of Eu3+ ion increases with the increasing Eu3+concentration. The reduced lifetime and the luminescence quenching of the 5d1 (Ce3+) level are due to the energy transfer from Ce3+ to Eu3+ ion. The efficiency of the energy transfer process from Ce3+ ions to Eu3+ ions and the nature of this interaction mechanism were determined by applying Reisfeld and Inokuti-Hirayama models.