Microwave sol-gel process of KGd(WO4)2:Ho3+/Yb3 phosphors and their upconversion photoluminescence properties

Abstract

Double tungstate KGd1−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 by the microwave sol–gel method, and the upconversion mechanisms were investigated in detail. The synthesized particles formed after heat-treatment at 900°C for 16h showed a well crystallized morphology with particle sizes of 2–5μm. Under excitation at 980nm, the UC intensities of KGd0.7(WO4)2:Ho0.1Yb0.2 and KGd0.5(WO4)2Ho0.05Yb0.45 particles 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, which were assigned to the 5S2/5F4→5I8 and 5F5→5I8 transitions, respectively. The Raman spectra of the doped particles indicated the presence of strong peaks at higher frequencies of 764, 812, 904, 984, 1050, 1106, 1250 and 1340cm−1 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.