Luminescence of nanocrystalline ZnS:Pb²⁺

Abstract

Nanocrystalline ZnS:Pb2+ 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:Pb2+ shows a white emission under UV excitation. At least two luminescence centers are involved. One center is identified as a Pb2+ ion located on a regular Zn2+ site and gives a red emission under 480 nm excitation. The luminescence properties of this emission are characteristic for transitions on Pb2+ 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 Pb2+. The green emission probably originates from a charge-transfer like D-band emission of Pb2+ in ZnS close to a defect (e.g. an S2− vacancy or an O2− ion on an S2− site). A relation between the temperature quenching of the emissions and the band gap is observed and indicates that photoionization occurs.