Induced ageing of ZnS:Ag microparticles exposed to 13 keV electron beam

Abstract

Phosphorescent microparticles made of ZnS:Ag were exposed to pulsed electron beams with an energy of 13 keV for periods of time between 30 min and 240 min. An XRD analysis showed no modification of crystalline structure. The average cristalites of ZnS:Ag was 62 nm deduced from SEM imaging. The luminescence spectra showed a decreasing activity with 40% after 30 min of irradiation at a fluence of 5.79 ×1016 electrons/cm2. The broad peak between 445 nm to 480 nm centered aroud 460 nm with a FWHM almost constant aroud 80 nm show no shifting. After a long exposure (over 240 min) and a fluence of 4.60 ×1017 electrons/cm2, the powder suffered a blackening effect attributed to formation of dead layers under electronic excitation combined with increasing of Sulphur vacancies, quantitatively confirmed by EDS analysis, where the proportion of S in ZnS:Ag decreases from 31.42% to 13.75%. Also, the luminescence at this moment dropped to almost 90% under the electron beam effect. The thermal effect could not be correlated with luminescence quenching, which was attributed to the increase in the number of impurities.