Direct impact excitation of thulium (III) luminescence in polycrystalline ZnO: Tm3+ electrodes in contact with an aqueous electrolyte, and attribution of the luminescence spectrum

Sintered polycrystalline semiconducting zinc oxide has been doped with Tm3+ ions and mounted as electrodes. Their electro-luminescence, studied under anodic polarization shows the characteristic luminescence spectrum of the doping Tm3+. The excitation of the rare earth is shown to result from a direct impact excitation process induced by hot electrons. The two main emission peaks of Tm3+, found at 480 and 805 nm, originate from two different Tm3+ levels, the former from 1G4 (1G4-->H-3(6) transition) and the latter from H-3(4) (H-3(4)-->H-3(6) transition).