Surface analysis and cathodoluminescence degradation of undoped ZnO and ZnO:Zn phosphors

Commercial ZnO:Zn and undoped ZnO with a hexagonal wurtzite structure (JCPDS 80-0075) were studied. The direct optical bandgaps were 3.25 and 3.28 eV for the undoped and ZnO:Zn, respectively. Undoped ZnO exhibited strong ultraviolet band to band emission as well as weak deep level defect emission around the green, orange, and red regions. ZnO:Zn emits only green light centered at 514 nm which was attributed to oxygen vacancies. Electron irradiated degradation of the ZnO:Zn sample showed a rapid initial decrease in cathodoluminescence intensity and then a subsequent recovery and increase to up to double the initial value during prolonged electron irradiation. Deconvoluted peaks of the O1s x-ray photoelectron peaks confirmed the presence of oxygen-related defects in both samples. The ZnO:Zn sample was found to be very stable under electron bombardment, which makes it suitable for the use in field emission displays.