In this work it is shown that CaZnOS:Eu 2+ has no Eu 2+ emission even at low temperature. The observed and earlier reported red emission originates from a CaS:Eu 2+ impurity phase. By means of washing the as-prepared samples with diluted nitride acid, we are able to remove the CaS impurity and get the pure CaZnOS. A clear relation was found between the red emission intensity, the CaS XRD line intensities and the nitric acid solution washing time, with zero intensity after prolonged washing. Later, a so-called VRBE (vacuum referred binding energy)-diagram was constructed showing the energy of the 4f n and 4f n-1 5d 1 states of the divalent and trivalent rare earth ions as dopants in CaZnOS with respect to the vacuum energy. This diagram shows that the 5d-levels of Eu 2+ are located in the conduction band, which explains the absence of 5d→4f emission. By comparing the VRBE diagram with diagrams of other related compounds like CaO, CaS, ZnO and ZnS it becomes clear that the Eu 2+ luminescence quenching is caused by a low lying conduction band, typical for Zn-based compounds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.