Synthesis and photoluminescence properties of fluorite-related (Y_1-xEu_x)₁₀W₂O₂₁ phosphor

Eu³⁺-doped fluorite-related yttrium-tungsten oxide Y₁₀W₂O₂₁ (5Y₂O₃ · 2WO₃) was prepared using vibrating-mill-mixed powder and solidstate reactions. The synthesis temperature was investigated by thermogravimetric/differential thermal analysis and X-ray diffraction. The morphology of the phosphor was confirmed by scanning electron microscope (SEM) measurement. The photoluminescence (PL) properties, including the excitation and emission spectra, decay curves (lifetime), thermal stability and quantum efficiency, were investigated. The PL emission intensity was found to increase with Eu³⁺ content up to about 22.5 mol% and then decrease due to the concentration quenching effect. There were two kinds of coordinating site (seven-fold coordination and eight-fold coordination) of Y³⁺ ions in the fluorite-related structure of Y₁₀W₂O₂1. Eu³⁺ in different coordinating sites of Y³⁺ in the host could lead to energy-level splitting of the ⁵D₀ - ⁷F₂ transition, resulting in an emission peak red shift. The major intensity emission wavelengths, located at 612 nm and 627 nm for excitation at 392 nm, were attributed to replacement of the Eu³⁺ ions with 7 or 8 coordination sites of Y³⁺ ions.