Relationship between structural characteristics and photoluminescent properties of (La1−xEux)2M2O7 (M=Zr, Hf, Sn) pyrochlores

Eu-doped pyrochlores, La₂M₂O₇ (M=Zr, Hf, Sn), were synthesized by solid-state reaction at a temperature range of 1473 and 1673 K, and their structures and optical properties were characterized by X-ray Rietveld analysis, field emission scanning electron microscope (FE-SEM), and photoluminescent spectroscopy. The Rietveld analysis indicated that the distortion of the (EuO₈)ⁿ⁻ scalenohedra increased with decreasing ionic radii of the M⁴⁺ ion, and the crystallinity increased with the sintering temperature. The splitting width of ⁵D₀-⁷F₁ transition of Eu³⁺ ions increased with the distortion of the (EuO₈)ⁿ⁻ scalenohedra. The luminescent intensity ratio of magnetic dipole transitions to electronic dipole transitions decreased with the crystallinity, and the chromaticity changed from deep-red to orange-red. The relationship between the chromaticity of phosphors and the crystallinity was clarified, and the control of crystallinity is an important factor that provides phosphors with required chromaticity.