Dieter Wadow

Phosphor degradation under electron excitation with varying anode voltage

A model for the variation of phosphor Coulomb degradation with anode voltage is presented, using the volume energy density as scaling parameter. With reference to the bulk phosphor degradation at 30 kV Coulomb degradation down to 2 kV has been calculated. A result of this model is that the degradation at a given charge dose increases with decreasing anode voltage. Considering the high charge doses accumulated in low-voltage displays operated at CRT brightness, only phosphors which are stable at 30 kV are expected to be applicable at low voltages. The predicted phosphor degradation at 4 kV is experimentally confirmed for oxide, silicate, and oxy-sulfide phosphors. For zinc sulfides the degradation measured at 4 kV is much faster than predicted, pointing to considerable contributions of surface-related effects.