Luminescence of ZnS:Cu,Br phosphors considering enhanced diffusion in two-phase system and percolation phenomena

The percolation-like effect of sharp increase of radioluminescence intensity with the rise of wurtzite phase content in sphalerite-wurtzite mixed phase composition ZnS:Cu,Br phosphors has been observed. This result was analyzed using percolation theory, considering that formation of the composite sphalerite-wurtzite matrix promotes the expansion of the interphase border square and the activator coactivator (Cu + and Br − ) diffusion along this border forming the luminescence centers as donor-acceptor Cu ’ Zn -Br S ● . So, the curtain content of the wurtzite phase promotes the continuous diffusion pathways formation on the interphase border and improves luminescence centers forming ability. To quantify the wurtzite-sphalerite interface effect in the phosphor grain on the effective diffusion coefficients of activating impurity ions a model was developed for different ratios of the diffusion coefficients along the interphase boundary to the diffusion coefficients in the bulk of the single phase. Considering that increased diffusion results in formation of larger amount of luminescent centers and higher luminescence intensity, good agreement between model and experimental results is found.