New insights on the energy transfer mechanisms of Eu-doped CdS quantum dots

Abstract

Eu-doped CdS quantum dots (QDs) with the Eu dopant concentration in the range of 0.5–10% and zinc blende (ZB) structure were successfully synthesized by a wet chemical method. The fabricated Eu-doped CdS QDs exhibited emissions in the visible window approximately at 465, 590, 618 and 696 nm, which correspond to the excitonic emission of CdS QDs and the electronic transitions of the intra 4f⁶ configuration from the ⁵D₀ level to ⁷F₁, ⁷F₂ and ⁷F₄ levels of Eu³⁺ dopant ions, respectively. Judd–Ofelt theory was used to estimate the properties of ligand field and luminescence quantum efficiency of the material. The interaction mechanism and the efficiency of the energy transfer process from CdS QDs to Eu³⁺ ions were found by using Reisfeld's approximation formulas. The luminescence quenching of Eu³⁺-doped CdS QDs was studied through analysis of emission spectra and decay curves. The dominant interaction mechanism between Eu³⁺ ions and energy transfer parameters have been found by fitting the decay curves to the Inokuti–Hirayama model. The cross-relaxation channels leading to the luminescence quenching of Eu³⁺ have also been predicted.