Preparation of high-performance luminescent oxide materials and investigation of the local structure surrounding luminescent centers by means of magnetic resonance spectroscopy

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1. Preparation of oxide luminescent materials such as EU(II)-doped alkaline aluminates, Eu(II)- and Dy(III)-doped strontium borophosphate and zinc oxides are examined along with the local structure surrounding luminescent centers by means of magnetic resonance spectroscopy. For the long phosphorescent Eu(II)-doped alkaline aluminates it was clarified that the Eu(II) and Dy(III) ions occupy two different low symmetry Sr sites by high frequency EPR spectroscopy. Also, photo-EPR examination using UV-irradiation suggested that there are defects near Dy(III) sites. Consequently, the mechanism of the long phosphorescence was proposed. As for the X-ray storage phosphor of SrBPO_5 : Eu it was found that there are two Eu(II) sites. It is for the first time that the EPR spectra of the low symmetry Eu(II) sites in polycrystalline materials are successfully analyzed.2. In order to examine the high frequency EPR spectra of ^8S ground state ions Fourier transformed Monte Carlo and Full Monte Carlo EPR spectral simulation programmes were developed. It is found that although the FT Monte Carlo method is as fast as the commercially available software, the calculated spectral line shape is far better than the latter one.3. For ZnO, which is one of the promising materials with UV emission, the expitaxial growth were examined using zinc halides as starting materials. Growth techniques of halide vapor expitaxy and atomic layer epitaxy under atmospheric pressure are developed.4. When the epitaxila ZnO films were grown on a sapphire (001) substrate, it was found that there is a difference in photoluminescence properties between halides used as starting materials. The ZnO films prepared using ZnI_2 showed an emission at about 380 nm at room temperature, while the films prepared using ZnCl_2 showed no emission. EPR spectroscopic investigation proved that the former films contain little defects in them.