Luminescent properties and energy level structure of CaZnOS:Eu 2+

Abstract

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.

Novel dual spectral conversion via Eu2+, Cu+-coactivated core–shell-structured CaS@CaZnOS phosphors for efficient photosynthesis of plants

“…Just as little Eu 2+ penetrates the cladding layer, CaZnOS:Eu 2+ also has no luminescence because the Eu 2+ 5d states are in the conduction band. 44 As the concentration of Cu + doped on the shell increases, the excitation and emission peaks show a redshift (as in Fig. 3(e) and (f)).…”

Novel Dual-Excitation and Dual-Emission Materials: Eu2+,Pb2+ Co-doped Core–Shell-Structured CaS@CaZnOS Phosphors and Their Application for Highly Efficient Photosynthesis of Plants

“…It is necessary to explain that due to the mechanism of inward erosion growth, some Eu 2+ also migrates from the CaS:Eu 2+ core to the CaZnOS shell during the synthesis process, but CaZnOS:Eu 2+ does not lead to any luminescence. 45 On the other hand, a small amount of Pb 2+ may enter the CaS core lattice forming CaS:Eu 2+ ,Pb 2+ . It has been reported that energy transfer from Pb 2+ to Eu 2+ occurs in the CaS:Eu 2+ ,Pb 2+ phosphor, resulting in enhancement of the Eu 2+ red emission.…”

Sensitizing Full‐Spectrum Lanthanide Luminescence within a Semiconductor CaZnOS Host

“…However, the emission of Sm 3+ , Eu 3+ , and Yb 3+ ions was quenched in the presence of the Cu + dopant, probably due to the charge transfer mechanism as judged by the high tendency of these ions to accept electrons (Figure S12, Supporting Information). [ 24 ]…”