AC Electroluminescence of ZnS : Tm

The ac electroluminescence of thulium‐doped embedded in boric acid matrix was investigated. The El emission spectra were recorded as a function of voltage, frequency, and temperature. The emission spectra at all temperatures show only strong sharp emission lines which were assigned to transitions within the 4f shell of Tm 3+ ion. The emission spectra consisted of five groups of lines centered around , , , , and . The emission intensities of different peaks were recorded as a function of the applied voltage . The plot of natural logarithm of shows a straight line characteristic over many orders of emission intensity which indicates that the direct impact excitation mechanism is a dominant process. The experimental values of the 483 emission line (transition ) intensity vs. the applied voltage were reproduced theoretically on the basis of the direct impact excitation mechanism.