Electroluminescence of Ho3+ ions in semiconducting polycrystalline zinc oxide electrodes in contact with aqueous electrolyte

Abstract

Sintered semiconducting zinc oxide has been doped with varying amounts of Ho³⁺ ions and its electroluminescence has been studied under various polarization conditions. Under cathodic polarization and in the presence of persulfate ions, the emission of the ZnO matrix only was observed. Conversely, under anodic under anodic polarization, characteristic emission bands of the Ho³⁺ ions were generated. The intensity of these bands was studied as a function of both the polarization potential and the rare earth doping level. In the 9.8–10.2 V vs. SCE range, the log of the emission intensity varied inversely with the square root of the applied potential, according to the Alfrey–Taylor relationship. It showed a maximum for a Ho³⁺ doping level of ca. 0.5 atom%. Analysis of the samples' polycrystalline structure using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques indicates that the rare-earth ions create islands on the surface of ZnO which induce dislocations in the polycrystalline structure.