Design of Phosphor Materials for White Light Source by Control of 4f Electronic Transition Probability of Rare Earth in Solids

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With the development, empowering and cost reduction of blue light-emitting diodes (LED), R＆D of white LED utilizing blue LED have become more and more active, promoting an expectation of highly efficient white light sources that would replace the fluorescent tubes.In this project, based on the above background, we started the research on development of novel phosphor materials that can be excited by blue LEDs and blue-violet laser diode (LD) and on the wavelength design, material fabrication and precise evaluation of their optical properties. Materials as targets are as follows; (I) broad visible fluorescence of Ce^<3+> ions in single crystalline and solid solution garnet crystals, their wavelength variation, quantum yields, color coordinates of emission spectra combined with blue LED, (II) YAG glass ceramic materials which show high excitation efficiency and high transparency, (III) We originally focus on Sm^<3+> doped phosphors with strong excitation band at 405nm, for power-illumina … More tion device with blue-violet LD and developed glass phosphors, investigated the relationship between composition and ligand-field parameters, spectra, transition probability, quantum efficiency and the quantum yields measured with an integrating sphere. It is possible to apply the Judd-Ofelt analyses for transparent glass samples and to calculate the Judd-Ofelt parameters for estimating the quantum efficiency combined with the lifetime data. We have successfully compared the systematic data of semi-theoretical value and experimental values obtained directly from the total flux measurement.For the YAG-based glass ceramics, we confirmed the luminous efficacy comparable to that of commercial white LEDs and proposed a patent.In summary, we conducted systematic studies on rare-earth doped phosphor materials including development of novel materials and evaluation of optical properties based on 4f electrons and of device performances as a solid-state lighting device, both experimentally and theoretically. Less