PHOTOLUMINESCENT CHARACTERISTICS OF LITHIUM-DOPED ZINC-OXIDE FILMS DEPOSITED BY SPRAY-PYROLYSIS

Lithium-doped and undoped zinc oxide photoluminescent films prepared b y the spray pyrolysis technique have been studied. The photoluminescen t emission for the Li-doped films is formed by a broad band composed o f the overlapping of four peaks at 508, 590, 604 and at similar to 810 nm; undoped films present the well known blue-green emission characte ristic of ZnO. The photoluminescent excitation spectra indicate that t he excitation mechanism is primarily due to electron-hole pair generat ion across the ZnO energy bandgap, although the excitation spectra als o show two smaller peaks at 508 and 524 nm, which seem to be related t o an electron excitation to localized states within the bandgap. The d ecay time measurements of the photoluminescence show that the lifetime of the luminescence emission is of the order of 187 ns. The behavior of the luminescent intensity with temperature shows an activation ener gy of 0.057 eV for competitive non-radiative transitions. (C) 1997 Els evier Science S.A.