Saturation of ( Zn , Cd ) S : Cu , Al Cathodoluminescent Phosphors at High Current Densities: I . Experimental Phenomena

Abstract

Efficiency loss due to high electron beam current density in green‐emitting phosphors has been measured for Cu and Al concentrations ranging from 27 to 1500 ppm. The severe loss of efficiency exhibited by commercial phosphors with activator concentrations in the 20–75 ppm range is somewhat alleviated at higher concentration. However, the improvement is far less than expected from a simple activator‐depletion model, and saturation effects are nearly constant from 100 to 500 ppm, showing that a second mechanism for saturation is important in this material. It is also found that saturation is independent of repetition rate, but depends rather on the net dose of electron beam charge delivered in a single pulse or scan. Laser photoexcitation experiments in the blue and u.v. show that analogous saturation occurs for all modes of excitation. Thus the second saturation mechanism is neither a thermal effect nor electric field quenching. The second paper in this series will show that the second saturation mechanism in phosphors is excited‐state absorption.