Eu 3+ singly-doped and Eu 3+ /Sm 3+ co-doped ZnS quantum dots: structure, optical properties and energy transfer

In this study, Eu ion singly doped and Eu /Sm ions co-doped ZnS semiconductor quantum dots (QDs) were successfully synthesized using a wet chemical method in 1-octadecene (ODE) solvent. The successful doping of Sm and Eu ions into the ZnS host lattice and the composition and valence of the elements present in the sample were confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Structural and morphological studies revealed the presence of Eu -doped ZnS and Eu /Sm co-doped ZnS QDs of about 3-4 nm size with a zinc blende structure. The Judd-Ofelt (J-O) intensity parameters of Eu -doped ZnS QDs were determined from their fluorescence spectra. The optical properties of Eu /Sm co-doped ZnS QDs were studied by changing the Eu ion concentration and fixing the Sm ion concentration. The photoluminescence (PL) spectra of Eu /Sm co-doped ZnS QDs were obtained at an excitation wavelength of 403 nm ( H → P transition of Sm ions) in the 525-725 nm range. The effective energy transfer (ET) process from Sm to Eu ions was confirmed and explained in detail using the Reisfeld approximation and the Inokuti-Hirayama model. The CIE color coordinates of the Eu /Sm co-doped ZnS QDs were obtained using PL spectral data. Eu /Sm co-doped ZnS QDs exhibited a long lifetime and emitted warm red light. These interesting properties give Eu /Sm co-doped ZnS QDs great potential for applications in photovoltaics, photocatalysis, and biomarkers.