Preparation And Properties Of Rare-earth Doped ZnO

Zinc oxide (ZnO) and ZnO-based dilute magnetic semiconductors (DMSs) have attracted much of interest as they hold great potential for the applications in magneto-, photo-, spin-electronics and microwave devices due to their wide band gap (3.37 eV) and high exciton binding energy (60 meV). Rear-earth elements have excellent optical and magnetic properties because of theirunique atomic shell structures. Therefore, it is of great importance to explore the magnetic properties of rare earth metal doped ZnO and promote its applications such as in magneto-optical and spin electronic devices.. In this thesis, preparation of Eu doped ZnO films by radio frequency magnetron sputtering, investigations on the structural, optical and magnetic properties of the samples systematically, and discussions on the origin and mechanism of ferromagnetism in Eu doped ZnO films are presented. Additionaly, ZnO:(Al, Eu) phosphors are also prepared by solid reaction process and their structural and optical properties are also addressed.It was found that the Eu doped ZnO films deposited by sputtering exhibited the c-axis orientation. The results from structural and optical measurements revealed that Eu3+ ions successfully substitute for Zn2+ ions in the ZnO lattice. The magnetization measurements of the films showed that Zno.98Euo.02O film was diamagnetic at room temperature, and Zno.95Euo.05O film had a clear ferromagnetic loop. These results indicated that room temperature ferromagnetism can be obtained by proper quantity of Eu doing into ZnO. No impurity phase was found in Eu doped films with XRD, Raman spectroscopy and ZFC measurements, which demonstrated that the ferromagnetism is attributed to the intrinsic property of Eu doped ZnO films.The influence of deposition and annealing conditions on the structural and magnetic properties of Eu doped ZnO films was studied. Compared with the Eu doped ZnO films prepared by sputtering in 5% of oxygen content, defects were introduced due to the lack of oxygen for the samples sputtered in pure Ar ambience, which result in an increase of the saturated magnetization for Zno.95Euo.05O films and the transition from diamagnetism to ferromagnetism for Zno.98Euo.02O films. The Zno.95Euo.05O film deposited at a substrate temperature of 450℃in the same armbient of pure Ar exhibited c-axis orientation, while the sample deposited at room temperature in pure Ar showed poor crystallinity. The magnetization measurements of those samples showed that the saturated magnetization is greatly increased for the sample deposited at the substrate temperature of RT in pure Ar, indicating that the defects play a key role in the development of ferromagnetism in the Eu doped ZnO films, and the origin for the magnetic coupling in Eu doped ZnO could be associated with bounded magnetic polaron (BMP).The imputiry phase of cubic Eu2O3 was found in ZnO:(Al, Eu) phosphor prepared by solid reaction process. More Eu3+ ions incorporated in ZnO lattice and the content of cubic Eu2O3 was decreased for the samples with increasing Al concentration. The room temperature photoluminescence (PL) spectra showed that there was a broad white-light emission covering nearly the whole visible-light range for the ZnO films codoped with Al and Eu. The Gaussian fitting curves of the PL spectrum of the sample revealed that the white-light emission consists of the 5D0→7F2 transition emission of Eu3+ ions and the emissions corresponding to impurity and defect levels in the films.