Design and Luminescent Properties of Ce3+-Activated Oxide Phosphor

Ce³⁺ ion has been usually used as an activator in the white LEDs phosphor because Ce³⁺-activated phosphors have a strong optical absorption at wide light region from UV to blue light and exhibit broad emission band owing to the 5d-4f transition of Ce³⁺. Because 5d orbital electrons are not shielded by outer 6s and 6p orbital electrons, the excitation and emission band position of Ce³⁺-activated phosphors is strongly affected by the crystal structure of host materials.¹⁾ According to the crystal field theory, the energy splitting of 5d excited level generally increases when Ce³⁺ occupied in the compact site with short bonding length in host lattice.²⁾ The larger energy splitting will contribute to shift the excitation and emission band of Ce³⁺-activated phosphors to longer wavelength side. From the viewpoint of the crystal field theory, we have been selected the oxide materials including 5, 6 or 7 coordination site with short bonding distance in the lattice of host materials to develop novel white LEDs phosphor that show excitation and emission spectra at longer wavelength region. As a result, we could successfully synthesize the novel red emission phosphors,^3,4) and in this study, we presents the luminescence properties of the novel oxide phosphors developed. In this study, we present our design concept for development of novel white LEDs phosphors and luminescence properties of Ce³⁺-activated phosphors designed by our original materials design concept.

This work was supported by a project from NEDO, New Energy and Industrial Technology Development Organization (Rare Metal Substitute Materials Development Project Development of Technology for Reducing Tb and Eu Usage in Phosphors for Fluorescent Lamp by High-speed Material Synthesis and Evaluation).

References

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