Study of optical properties and energy transfer mechanism of Tb3+, Sm3+ singly doped and co-doped ZnS quantum dots

For the first time, Tb3+ and Sm3+ ions co-doped into semiconductor ZnS quantum dots (QDs) were successfully synthesized by a wet chemical method. The presence of Tb3+ and Sm3+ ions in ZnS QDs was verified by X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) and UV–visible absorption spectra analyses revealed that the as-synthesized QDs had a zinc blende (ZB) structure with a particle size of about 3–4 nm. The optical properties of Sm3+ ions in ZnS QDs were studied through the excitation, photoluminescence (PL) spectroscopy, and PL-decay lifetime by using the Judd-Ofelt (J-O) theory. The luminescent quenching phenomenon of Sm3+ was observed when its concentration was higher than a specified value. For the ZnS QDs co-doped Tb3+ and Sm3+, the luminescent intensity of Sm3+ ions was enhanced because of the energy transfer (ET) process from Tb3+ ions to Sm3+ ions. The main interaction mechanism for the Tb3+-Sm3+ and Sm3+-Sm3+ energy transfer processes was determined by using the Inokuti-Hirayama (I–H) model.