Multimodal luminescence properties of surface-treated ZnSe quantum dots by Eu

ZnSe:Eu quantum dots (QDs) were synthesized using the heating-up method by adding a Eu precursor in Zn and Se precursors. The optical property was investigated based on the change in the multimodal emission caused by increasing the amount of the Eu precursor. The emission wavelength of ZnSe QDs increased from 398 nm to 405 nm when the reaction was carried out for 30-300 s. The broad spectrum was attributed to the 4F65D1 → 4F7 transition when the Eu2+ emission was increased from 450 to 550 nm. Eu3+ shows characteristic red emission peaks at 579, 592, 615, 651, and 700 nm owing to the electronic transition of 5D0 → 7Fj (j = 0, 1, 2, 3, 4). The expected structure of the ZnSe:Eu QDs was verified by XRD, TEM, and XPS. Compared to the diffraction peaks of pristine ZnSe, the corresponding peaks for the ZnSe:Eu QDs are shifted, by about 0.43°, to larger angles, because the ionic radius of Eu3+ (0.95 Å) is larger than that of Zn2+ (0.74 Å). They also have Eu2+O and Eu3+O dangling bonds on the surface of Eu3+-doped ZnSe QDs, with an average size of about 3.15 nm. These semiconductor QDs with rare earth elements are promising candidates to fabricate light-converting materials.