Noise and modulation experiments on cathodoluminescence from a Sr3(PO4)2-Tb phosphor

Abstract

The kinetics, energy efficiency and mutual correlation of the 5D4 - 7Fj and 5D3 - 7Fj j=0, 1,..., 6, emissions of the Tb3+ ion in a Sr3(PO4)2-Tb phosphor were investigated under cathode-ray excitation with energies between 1·5 and 9 keV. The kinetics were determined from the luminescent response on pulsed and sinusoidally modulated excitation. It was found that the 5D3 emission is a rather complex process with a main decay time of 2·3 ms, independent of the primary electron energy in the range considered. The 5D4 emission showed two characteristic times: one of 6·0 ms, which is associated with the decay of the 5D4 state to the 7Fj ground state, the other of 0·75 ms, with the decay of an unknown level X to the 5D4 state. Both times appeared to be independent of cathode-ray energy. However, the ratio of excitations from the ground state to the X state, compared with the 5D4 state, increased by a factor of 2·5 between 2 and 8 keV. AC modulation response and pulse response were in good agreement with each other. The frequency-dependent part of the light noise was measured between 1 and 1000 Hz. The energy efficiency of the phosphor, determined from the low frequency value of the noise in excess of full shot noise, agreed fairly well with the 1968 results of Bril et al.. The correlation coefficient of the 5D3 and 5D4 emissions measured at low frequencies between 2 and 8 keV agreed reasonably with theory.