Luminescence of nanocrystalline ZnS:Pb~(2+)

摘要

Nanocrystalline ZnS:Pb~(2+) is synthesized via a precipitation method. The luminescence is studied and the influence of the size of the nanocrystals on the luminescence properties is investigated. Nanocrystalline ZnS:Pb~(2+) shows a white emission under UV excitation. At least two luminescence centers are involved. One center is identified as a Pb~(2+) ion located on a regular Zn~(2+) site and gives a red emission under 480 nm excitation. The luminescence properties of this emission are characteristic for transitions on Pb~(2+) ions. The other centers are not as well defined and give a broad green emission band under 380 nm excitation and also show luminescence properties typically observed for Pb~(2+). The green emission probably originates from a charge-transfer like D-band emission of Pb~(2+) in ZnS close to a defect (e.g. an S~(2-) vacancy or an O~(2-) ion on an S~(2-) site). A relation between the temperature quenching of the emissions and the band gap is observed and indicates that photoionization occurs.