Strong room-temperature ultraviolet emission from nanocrystalline ZnO and ZnO:Ag films grown by ultrasonic spray pyrolysis

Nanocrystalline ZnO and ZnO:Ag films have been deposited on Si (1 0 0) substrates by ultrasonic spray pyrolysis (USP) technique under ambient atmosphere. Among pure ZnO films, the sample deposited at 500 °C with spray rate of 0.15 ml/min has the strongest near-band edge (NBE) ultraviolet emission (378 nm) observed in the room-temperature photoluminescence (RT PL) measurement. Its PL intensity ratio (R) of the UV emission to the deep-level emission has a largest value of 470 and the full-width at half-maximum (FWHM) of UV peak has a smallest value of 10 nm (87 meV). Moreover, RT PL spectra show that compared with undoped ZnO, the UV emission intensity of ZnO:Ag films (with the Ag:Zn atomic ratio = 3% in the precursor solution) is even markedly enhanced and the R increases to the value of at least 700. However, a silver phase is detected and the UV luminescence becomes weak for ZnO:Ag films after the annealing at 700 °C in air for 1 h.