Red-orange photoluminescence emission of sol-gel dip-coated prepared ZnO and ZnO:Al nano-crystalline films

Zinc oxide films doped with 0-5 % wt. Aluminum (AZO) were prepared by sol-gel method and coated on glass substrate via dip-coating process. The sol was obtained with 0.5 M ethanolic solution of zinc acetate deposited into glass substrate with 200 mm/min withdrawing speed for 3 times. The deposited films were transformed into nanocrystalline undoped or Aluminum-doped ZnO after heat treatment at 400 degrees C for 2 h. Processing conditions and the effects of Al doping on crystallinity, morphology, and optical properties of ZnO films were characterized by X-ray diffraction (XRD), FESEM analysis, UV-VIS and photoluminescence spectroscopy. XRD analysis confirmed that all nano structured thin films have a hexagonal wurtzite structure. Results showed that Al doping has considerable effect on particle size, absorbance, transmittance and photoluminescence emission of samples. Depending on the Al concentration film transparency significantly increased, the highest transparency greater than 80% for 3 wt % AZO prepared films has been acquired. Accordingly the calculated optical band gap energy was varying from 3.2 to 3.7 eV related to Al doping level. The photoluminescence studies of undoped ZnO and AZO films have revealed very interesting features. Correspondingly photoluminescence spectra indicated that elaborated undoped ZnO and AZO films could emit luminescence emission over the entire visible region included violet emission peak at 413 nm, blue emission peak at 487 nm, green emission peak at 531 nm and orange-red emission peak at 630 nm that later is not very common in ZnO which is mainly attributed to Oi-related transitions.