Optical properties of dye sensitized zinc oxide thin film deposited by sol-gel method

Abstract

Metal oxide semiconductor has been widely studied due to it varied properties and application. Among metal oxide, ZnO semiconductor is of great interest due to wide band gap (3.2-3.4eV) with hexagonal wurtzite structure. This study involves the comparison of optical properties of ZnO thin films when doped with erbium and terbium. The optical properties were studied using Photoluminescence and Direct Reflector ultraviolet (DR-UV). FESEM image shows that the irregular shape and there is variation in the surface morphology of undoped and doped ZnO thin film. The grain size increased with addition of erbium and terbium. The transmission spectra for all samples show high transmission with more than 90%. However the band gap increase for doped ZnO thin film sensitized with eosin B. The band gap value also decreases with the addition of erbium and terbium for sensitized eosin Y. The XRD patterns of these samples are in close agreement with the JCPDS standard (No. 36-1451). It was observed that all deposited films were polycrystalline with hexagonal wurtzite structure with diffraction peaks oriented along the (100),(002),(101),(102),(110) and (103) planes. The preferred orientation for ZnO thin film sensitized with eosin Y and B is (101) plane. The discrepancy may be caused by different preparation condition. The PL emission in the UV bands was observed, peaking at the range of 365-387nm, centered at 380 at near band edge emission, due to Er3+ transition from 4F7/2?4I15/2 and Tb3+ transition from 5D4?7F1.