Microwave-Assisted Sol-Gel Preparation of KY(WO4)2:Ho3+/Yb3+ Yellow Phosphors and Their Upconversion Photoluminescence Properties

Abstract

Double tungstate KY_1-x(WO₄)₂:Ho³⁺/Yb³⁺ yellow phosphors with doping concentrations of Ho³⁺ and Yb³⁺ (x = Ho³⁺ + Yb³⁺, Ho³⁺ = 0.05, 0.1, 0.2 and Yb³⁺ = 0.2, 0.45) were successfully prepared by the microwave-assisted sol-gel method and their upconversion photoluminescence properties was investigated. Well-crystallized particles, formed after heat-treatment at 900 °C for 16 h, showed a fine and homogeneous morphology with particle sizes of 2-5 μm. Under excitation at 980 nm, the upconversion intensity of KY_0.5(MoO₄)₄:Ho_0.05Yb_0.45 phosphor exhibited yellow emissions based on a strong 550 nm emission band in the green region and a strong 655 nm emission band in the red region. The Raman spectra of the particles indicated the presence of strong peaks at higher frequencies and a weak peak at lower frequency induced by the disorder of the [WO₄]^2- groups with the incorporation of the Ho³⁺ and Yb³⁺ elements into the crystal lattice or by a new phase formation.