Preparation And Optical Properties Of Zinc Oxide Thin Films Doped With Rare Earth Europium Lons

Zinc oxide, one of the most promising materials, has been demonstrated to be applicable in solar cells, lighting-emitting diodes, room temperature ultraviolet lasers, gas sensor, field-effect transistors and piezoelectric-gated diode. It has attracted increasing interest in fabricating ZnO structures with designed morphology and properties while the desired optical and electrical properties could be achieved by doping ZnO with various elements. ZnO is a semiconductor with wide band-gap (3.37 eV) and high exciton-binding energy (60 meV) that allow efficient ultraviolet excitonic emission even at room temperature, as short wavelength UV light-emitting diode and laser, it can improve the storage density of computer. Moreover, ZnO is a good host material for doping of impurities because of its good mechanical,thermal and chemical stability. Because the RE3+ ions have special shell structure, the outside crystal field is shielded by the electronic shell. Their emission peaks usually involve 4f-4f transitions. The RE3+ ions have a great deal of characteristic sharp emission peaks in near ultraviolet, visible and near infrared spectral region, so it can be a luminescence center of luminescence materials. The RE3+-doped zinc oxide optoelectric thin films not only can rich the colors emitted by ZnO, but also can provide important value of fundamental research for optoelectric integrated materials and device. The RE3+-doped semiconductor has been widely applied in some electroluminescent thin film devices, photoelectron and cathode ray light-emitting device. In this work, ZnO and Eu-doped ZnO thin films were deposited on quartz substrates by reactive radio-frequency magnetron sputtering from a ZnO and Eu-doped ZnO ceramic target respectively. The structure and optical properties were studied. High quality thin films with preferential c-axis orientation and strong UV emission in ZnO thin films were obtained. Under UV excitation. the prepared Eu-doped ZnO thin films have high energy transfer from the host to Eu3+ and luminous efficiency that can be used for lighting and display application The main works are summed up as follows:First, the Eu3+ ions doped ZnO ceramic targets were prepared by high-temperature solid-state reaction. High-temperature solid-state reaction is a kind of traditional optical materials synthesis method. By controlling the reaction conditions (temperature and reaction atmosphere in roasting process), reductant, fluxing agent and raw material, Eu3+ ions-doped ZnO target materials with high density and uniform quality were prepared.Second, the ZnO and ZnO:Eu thin films were grown onto the quartz substrate by (?)active radio-frequency magnetron sputtering from a ZnO and ZnO:Eu ceramic target with (?)RF-500 magnetron sputtering instrument, respectively. Magnetron sputtering is an efficient method to prepare thin films due to the advantages of large area deposition, low cost, smooth and uniform surface of thin films, so is widely used in the preparation of the thin film. The XRD patterns show that the thin films have excellent preferential c-axis orientation. There is no observable diffraction peaks related to Eu2O3 in ZnO:Eu thin film. It is found that the ZnO:Eu thin films have an UV near band edge excitonic emission band around 382 nm and four emission peaks at 580 nm,597 nm,618 nm and 660 nm attributed to 5Do→7Fo, 5Do→7Fi, 5Do→7F2 and 5Do→7F3 transitions of the Eu3+ ions, respectively. When the substrate temperature is at 250℃and the annealing temperature is at 600℃, the ZnO and ZnO:Eu thin films have good transmittivity in the UV region.Third, sol-gel method was used to prepare ZnO and ZnO:Eu nano wires using nanopore Al2O3 template. The SEM images show uniform growth of ZnO and ZnO:Eu nanowires. A strong UV near band edge excitonic emission band around 385 nm was observed and defect related green emission was absent in the photoluminescence spectra of the ZnO and ZnO:Eu nanowires samples under UV excitation with the wavelength of 337 nm. It is found that the intensity of UV emission is greatly decreased and moved to blue light when ZnO was doped with Eu3+ ions. The ZnO:Eu nanowires emit faint red light under above-bandgap energy excitation, demonstrating an energy transfer from the host to the rare earth ions.