Noise and modulation experiments on cathodoluminescence from ZnS-Ag

Abstract

The concept of luminescence from donor-acceptor transitions, introduced by Williams1), was applied to calculations of a.c. modulation response, spectral noise density, and emission spectrum of the radiation. These calculations were based on a donor-acceptor transition probability that decreases exponentially with their separation2, whereas donors and acceptors were assumed to be randomly distributed over the phosphor. The distribution of de-excitation probabilities was approximated by taking into account the statistical distribution in space of nearest neighbours only. The frequency dependence of squared a.c. modulation response (SMR) and spectral noise density (SND) were found to be identical at low excitation densities, whereas the frequency dependence of the SMR for a selected narrow wavelength band out of the emission spectrum was calculated to vary with wavelength.

Our theoretical results were compared with experiments on cathodoluminescence from ZnS-Ag, while some experimental results of Era et al. concerning the shift in the peak position of the emission with excitation density, were compared with our theoretical predictions. The agreement found gives an additional proof of the existence of the donor-acceptor mechanism for the blue luminescence of ZnS-Ag.