Photo and electroluminescence from terbium doped zinc sulfide films deposited by spray pyrolysis

Abstract

Undoped, silver doped and silver-terbium doped zinc sulfide photoluminescent thin films have been prepared by the spray pyrolysis technique. The crystalline structure of the deposited films is hexagonal wurzite, in all cases. The films have a preferential growth with the (0 0 2) direction perpendicular to the surface of the substrate. In general, the relative chemical compositions show that the films are formed by a zinc rich ZnS material. The photoluminescent excitation measurements are in agreement with the optical transmission results indicating that the excitation mechanism is related to electron–hole pair generation across the ZnS band gap. The photoluminescent spectra show the typical bands associated with the transition from the 5D4 level to the 7F6, 7F5, 7F4 and 7F3 levels of the Tb3+ ions. The emission spectra for the undoped and silver doped films show the well known self-activated emission, centered at 460 and 490 nm, respectively. The dependence of the emission intensity on the temperature shows an energy activation of 0.1 eV for competitive non-radiative transitions. Electroluminescent devices using silver-terbium doped zinc sulfide films as active layer show emission spectra similar to those observed in photoluminescence measurements but with a reduced intensity.