Emission and structure variations at aging ZnO:Ag nanocrystals prepared by spray pyrolysis

The emission and structure of ZnO:Ag nanocrystal (NC) films obtained by ultrasonic spray pyrolysis have been studied in the as-grown state and after aging. The scanning electronic microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) methods have been applied. The films are characterized by the wurtzite crystal structure with the NC sizes about of 8.0–10.0 nm in the as-grown state and 6.0–8.0 nm after aging in ambient air. The Ag content was varied within the range of 1–4 at.% in the ZnO films. PL spectra of as-grown ZnO:Ag films are complex and can be presented as a set of PL bands at 10 K: the near band edge emission with the peak at 3.18 eV, two Ag doping—related PL bands centered at 2.95 and 2.68 eV, and native defect-related green (2.40 eV) and orange (1.90 eV) PL bands. The high PL intensities of Ag doping-related PL bands were detected for the Ag concentrations of 2–3 at.%. PL intensities of high energy PL bands (3.18, 2.95 and 2.68 eV) fall down at aging together with intensity stimulating the orange and green PL bands. The joint analysis of XRD and PL results permit to confirm that the 2.95 eV PL band is connected with the optical transition via the substitutional Ag_Zn defects. It was shown as well that aging in ambient air is owing to the diffusion of oxygen interstitials in the ZnO:Ag NCs that leads to intensity increasing the orange PL band and modification of the Ag_Zn radiative defects.