Role of dopant concentration and surface coating on photophysical properties of CdS: Eu³⁺ nanocrystals

Abstract

Here, we report the role of dopant concentration and surface coating of CdS: Eu³⁺ nanocrystals on the modification of crystal structure and their photoluminescence properties by steady-state and time resolved fluorescence studies. It is found that photoluminescence properties are sensitive to the crystal structure which is controlled by surface coating and dopant concentration. The emission intensity of the peak at 614 nm (⁵D₀ → ⁷F₂) of the Eu³⁺-ions is found to be sensitive to the doping and surface coating of CdS nanocrystals. It is found that the average decay times 〈τ 〉 are 248, 353 and 499 μs for 0.25, 0.5 and 1.0 mol% Eu ions doped into CdS nanocrystals, respectively. From the decay time measurements, it is evident that the energy transfer occurs from CdS nanoparticles to Eu³⁺ ions and the calculated energy transfer efficiency from CdS nanoparticles to Eu³⁺ ions is 9.2 and 35% for Eu³⁺ ions coated and doped CdS nanoparticles, respectively. Our analysis suggests that site symmetry of ions plays a very important role in the modifications of radiative and nonradiative relaxation mechanisms.