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

Double tungstate KGd1-x(WO4)(2):Ho3+/Yb3+ phosphors with doping concentrations of Ho3+ and Yb3+ (x=Ho3+ 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 degrees C for 16 h showed a well crystallized morphology with particle sizes of 2-5 pm. Under excitation at 980 nm, the UC intensities of KGd0.7(Wo(4))(2):Ho0.1Yb0.2 and KGd0.5(Wo(4))(2)Ho0.05Yb0.45 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 S-5(2)/F-5(4) -> (5)i(8) and F-5(5) -> I-5(8) 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 1340 cm(-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. (C) 2014 Elsevier Ltd. All rights reserved.