ELECTROLUMINESCENT PROPERTIES OF POLYCRYSTALLINE ZINC-OXIDE ELECTRODES DOPED WITH ER-3+ IONS

Sintered semiconducting zinc oxide has been doped with various amounts of Er3+ ions and its electroluminescence has been examined under various polarization conditions. Under negative bias, and in the presence of persulfate ions, the only emission observed is that of ZnO which the rare earth fingerprints by partial absorption of the emitted light. From the efficiency of the reabsorption, it is deduced that the emission originates from (or near) the electrode-electrolyte interface. Under positive bias (> 9.8 V versus standard calomel electrode) two different emissions are observed which depend on the RE3+ doping ratio: below 0.02 at.% Er3+ a mixture of ZnO and Er3+ emissions are observed, while above 0.05 at.% Er3+ the main emission originates from the H-2(11/2), S-4(3/2) and F-4(9/2) levels of Er3+. The brightness of Er3+ emission follows an Alfrey-Taylor relationship indicating an acceleration-collision type of mechanism. It varies with the Er3+ concentration in ZnO and reaches a maximum at ca. 0.6 at.%. Time-resolved measurements carried out on the Er3+ emission indicate that the build-up and decay times on the electroluminescence are about the same, of the order of a few hundreds of microseconds. However, this decay time increases with increasing Er3+ concentration and reaches a minimum plateau of ca. 70-mu-s.