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

摘要

The Eu3+-doped ZnS nanocrystals prepared by the chemical method have a cubic structure. All the transitions D-5(0) -> F-7(J) (J = 0, 1, 2, 3, 4, 5, 6) of Eu3+ were observed in ZnS nanocrystals. In particular, the forbidden transitions of D-5(0) -> F-7(0), D-5(0) -> F-7(3) and D-5(0) -> F-7(5) 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 D-5(0) -> F-7(1) confirms the crystal-field analysis that in the first order approximation the crystal field has no effect on the multiplet F-7(1). The crystal-field analysis shows that the multiplet F-7(2) 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 F-7(4) were observed in the photoluminescence of the transition D-5(0) -> F-7(4), the crystal-field parameter B-0(6) was estimated from the width of the emission band of this transition. In accordance with the superposition model, the crystal-field parameters B-0(4) and B-0(6) were fitted to be -59.8 meV and 41.6 meV, respectively.