Synthesis of KLa(WO4)2:Ho3+/Yb3+ Phosphors via Microwave-Assisted Sol-Gel Route and their Upconversion Photoluminescence Properties

Abstract

Double tungstate KLa_1-x(WO₄)₂:Ho³⁺/Yb³⁺ 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 synthesized via the microwave-assisted sol-gel route and the upconversion of their 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 KLa_0.5(MoO₄)₄:Ho_0.05Yb_0.45 phosphor exhibited a strong 550 nm emission band in the green region and a very 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 weak peaks at lower frequencies 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.