Synthesis and optical properties of Pr3Â +-doped ZnO quantum dots

In order to increase the quantum efficiency of solar cells by down-conversion, Pr3 + doped semiconductor ZnO quantum dots (QDs) were successfully synthesized by sol-gel method. The X-ray diffraction (XRD) results indicate that ZnO QDs have hexagonal wurtzite structure and a part of the Pr3 + ions is incorporated into the ZnO lattice. ZnO QDs have a spherical shape and diameter around 5 nm, which was confirmed by the high-resolution transmission electron microscopy (HRTEM). The room-temperature photoluminescence (PL) measurements revealed both UV and visible emission from the ZnO QDs. The emission peaks of aged ZnO QDs show red shift due to a size increase of the QDs, i.e, the decrease of the band gap energy and modification of the defect states. The enhancement of the PL emission peaks at 578, 630, and 752 nm was assigned to energy transfer between Pr3 + ions and ZnO QDs host. The absorption peaks at 445, 470, 485, and 590 nm were observed only in Pr3 + ion doped ZnO QDs which confirms that the energy transfers from Pr3 + ions to ZnO QDs.