Hydrothermal assisted synthesis and photoluminescence of (Y1-xEux)2WO6 red phosphors

Abstract

Phase-pure (Y1-xEux)2WO6 (x = 0.2–0.11) red phosphors (average crystallite size ∼66 nm) in a monoclinic structure have been calcined at 1300 °C from their precursors autoclaved from the mixed solutions of rare-earth nitrate and sodium tungstate dihydrate (Na2WO4·2H2O) at 180 °C and pH∼10, instead of the commonly adopted pH values of 3–7, without the use of any surfactant. The materials were characterized in detail by the combined techniques of XRD, FT-IR, FE-SEM, TEM, EDS, and optical spectroscopy to reveal (1) the phase structure, morphology, and spatial cation distribution of the hydrothermal product, (2) the course of phase and morphology evolution that leads to the targeted tungstate phosphor, and (3) the effects of Eu3+ content on photoluminescence properties, including excitation/emission, asymmetry factor of luminescence (5D0→7F2/5D0→7F1 intensity ratio), fluorescence lifetime, and CIE chromaticity coordinates. Through energy transfer from the [WO6]6− ligands to Eu3+, the (Y1-xEux)2WO6 phosphors exhibit sharp 5D0→7FJ (J = 0–4) emissions upon UV excitation into the O2--W6+ charge transfer band peaked at 327 nm, with the red emission at 611 nm being the most prominent (5D0→7F2 transition of Eu3+). The optimal Eu3+ content was determined to be ∼9 at.% (x = 0.09), and concentration quenching of luminescence was analyzed to be owing to exchange interaction. The emission color moves closer to the red region in the CIE chromaticity diagram with increasing Eu3+ doping, while fluorescence lifetime of the 611 nm emission, analyzed to be around 1.05 ± 0.05 ms, shows weak dependence on the Eu3+ content.