Photoluminescent characteristics of lithium-doped zinc oxide films deposited by spray pyrolysis

Lithium-doped and undoped zinc oxide photoluminescent films prepared by the spray pyrolysis technique have been studied. The photoluminescent emission for the Li-doped films is formed by a broad band composed of the overlapping of four peaks at 508, 590, 604 and at ∼ 810 nm; undoped films present the well known blue-green emission characteristic of ZnO. The photoluminescent excitation spectra indicate that the excitation mechanism is primarily due to electron-hole pair generation across the ZnO energy bandgap, although the excitation spectra also show two smaller peaks at 508 and 524 nm, which seem to be related to an electron excitation to localized states within the bandgap. The decay 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 energy of 0.057 eV for competitive non-radiative transitions.