Low temperature study of the uv emission in sol-gel dip-coated silver-doped zinc oxide thin films

Abstract

Undoped and 3 at % Ag-doped ZnO thin films deposited on glass substrates by the sol– gel dip-coating technique have been studied. X-ray diffraction (XRD) measurements have revealed that the two films are polycrystalline and exhibit a ZnO hexagonal wurtzite structure with an average crystallite size of less than 5 nm. SEM images have demonstrated a homogeneous dispersion of the grains with a spherical morphology of the doped sample. The optical transmittance of the deposited films has indicated that the films transparency exceeds 80% in the visible range. The room temperature photoluminescence (PL) spectra have shown that the UV band (385 nm) intensity is not affected by Ag doping. The PL spectra of pure ZnO thin film have revealed that the bound exciton (BX) and the free exciton (FX) emissions are dependent on recorded temperature. The PL spectrum at 77 K of Ag-doped ZnO has demonstrated that doping with silver enhances BX and optical phonons replica (2LO) (centered at 3.168 eV) emissions. This result indicates that the peak observed at 3.168 eV is not only due to 2LO but also to the transition of electrons from the conduction band to a defect level induced by silver atoms in ZnO crystallites.

Keywords

• Ag-doped ZnO
• sol–gel
• dip-coating
• low-temperature photoluminescence
• thin films