Microstructure and luminescent properties of Eu₂W₂O₉ phosphors

A homogeneous Eu₂W₂O₉ phase with small grains (∼4.0μm) was formed for the specimens fired below 1175°C. As the firing temperature was increased above 1150°C, grain growth occurred and the grain shape changed from faceted to round. The excitation spectra of the Eu₂W₂O₉ phosphor were similar to those of the Eu₂(WO₄)₃ phosphor, but the absorption band due to the O²⁻→W⁶⁺ ligand to metal charge transfer was shifted to lower energies and the ⁷F_o→⁵H₃ and ⁷F_o→⁵F_2,4 transitions were not found. The intensity of the excitation and emission spectra of the Eu₂W₂O₉ phosphor considerably increased with increasing firing temperature, due to the increased grain size and changed grain shape. The intensity of the red emission band of the Eu₂W₂O₉ phosphor was higher than that of the Eu₂(WO₄)₃ phosphor. Moreover, the addition of LiCl to the Eu₂W₂O₉ phosphors considerably enhanced the intensity of their emission spectra, probably due to the increased grain size. Therefore, LiCl-added, Eu₂W₂O₉ phosphor is a promising candidate material for red color emission.