It is known that Cu is necessary and no-replacable for ZnS powder ACEL.For this reason

the stability of Cu and its pattern in ZnS particle is the most important for maintenance of luminescence.Cu

+

possesses a strong thermo-diffusion with diffusivity of about 10

-9

cm

2

/s in ZnS.At 900℃

ZnS particle of 7~10m can be activated by Cu

+

diffusion in few minutes completely.Cu

x

S is a fast-ion conductor emerging very strong Cu

+

migration in electric field.Because of high conductivity of Cu

x

S

Cu

x

S conductive line in ZnS grain is on the equipotential.The different equipotential surfaces from that of Cu

x

S line are distributed making a detour around the Cu

x

S line

not across the Cu

x

S line and compressed near both ends of Cu

x

S line.The most of current through the ZnS grain passed the Cu

x

S line because the direction of current must be vertical to the equipotential surfaces.So that

the density of current in the Cu

x

S line is not even

being the largest on the center

and weakening from the center to the ends gradually.