Photoluminescence properties of the Eu3+-doped ZnS nanocrystals and the crystal-field analysis

The Eu3+-doped ZnS nanocrystals prepared by the chemical method have a cubic structure. All the transitions 5D0 → 7FJ (J = 0, 1, 2, 3, 4, 5, 6) of Eu3+ were observed in ZnS nanocrystals. In particular, the forbidden transitions of 5D0 → 7F0, 5D0 → 7F3 and 5D0 → 7F5 were all observed and their observed values of energies were found to match well with those predicted from a complete diagonalization of the crystal-field Hamiltonian for Eu3+. The photoluminescence of the transition 5D0 → 7F1 confirms the crystal-field analysis that in the first order approximation the crystal field has no effect on the multiplet 7F1. The crystal-field analysis shows that the multiplet 7F2 has a doubly degenerate sublevel and a triply degenerate sublevel, which also agrees with the photoluminescence results very well. Although not all sublevels of crystal levels of multiplet 7F4 were observed in the photoluminescence of the transition 5D0 → 7F4, the crystal-field parameter B06 was estimated from the width of the emission band of this transition. In accordance with the superposition model, the crystal-field parameters B04 and B06 were fitted to be -59.8 meV and 41.6 meV, respectively.