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

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.

Influence of precursor ratio and dopant concentration on the structure and optical properties of Cu-doped ZnCdSe-alloyed quantum dots.

Tunable copper doped Zn1-x Cd x S alloy quantum dots (QDs) were successfully synthesized by the wet chemical method. A one-step method is developed to synthesize doped ternary QDs which is more preferable than a two-step method. The influence of experimental parameters like the Zn/Cd ratio and Cu dopant concentration has been investigated using various spectroscopic techniques like UV-visible, photoluminescence, X-ray diffraction and Raman spectroscopy. The absorption and emission properties can be tuned by changing the concentration of components of the ternary QDs. The high concentration of dopant completely quenched the emission of the ternary QDs. EDX gives confirmation of the elemental composition of the synthesized samples. The obtained results suggest the successful doping of the ternary QDs. Interestingly, the study results revealed that the crystal structure (ZB and/or WZ) and the dual emission of the Cu-doped Zn1-x Cd x Se alloy QDs could be controlled by varying the dopant concentration and chemical composition of the host. Doping also leads to enhancement in emission properties and provides more stability to ternary QDs. The enhancement in the photoluminescence (PL) decay lifetime of Cu-doped ternary QDs can be advantageous for optoelectronic and biosensor applications.