A bond valence analysis of electroluminescent ZnS:Cu, Cl to elucidate the aging mechanism

Brightness decay in electroluminescent (EL) phosphors is a diffusion-related phenomenon. Copper is shown to be the most easily diffusing species, although all diffusion is strongly influenced by the presence of sulfur vacancies or, to a lesser extent, halogen atoms substituting on sulfur sites. Diffusion is facile in the Cu2-xS which decorates the defects in EL phosphors, and bond valence sums harmonize well with the existence of a plethora of copper sulfide binary phases. Strategies for improving the useable lifetimes of EL phosphors are examined.