Investigation on self activated and copper activated zinc sulphide

The diamagnetic susceptibility of zinc sulphide decreases on heat treatment and becomes less temperature dependent. The susceptibilities or the differences in susceptibilities of the pure and activated samples do not obey Curie Law. The susceptibility follows a relation of the typeX _T =X ₀ +X ₁ e ^?E/KT in which bothX ₀ andX ₁ have the same sign.X ₀ is interpreted as true diamagnetic susceptibility of the sample and gradually increases in value with activation,X ₁ depends on the particle size and is found to decrease with the increase in particle size. This is interpreted as being due to surface electrons.“E” as measured in this way is found to be of the order of 0·01 ev. in all cases. Thus“E” seems to be the average surface trap depth of zinc sulphide. It has also been found that in zinc sulphide with low copper concentration the luminescent centres are diamagnetic; copper ions are present presumably in substitutional positions. For zinc sulphide containing high concentration of copper, the presence of paramagnetic centres are detected. It is suggested that in this case copper is present not only at the regular lattice positions acting as luminescent centre but also settles at special lattice sites like dislocation jogs.