Effects of Ho3+ and Yb3+ doping concentrations and Li+ co-doping on the luminescence of GdVO4 powders
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We present the structural and luminescent properties of Ho3+/Yb5+-doped GdVO4 and Li+-co-doped GdVO4:Ho3+/Yb3+ powder phosphors. The materials were prepared by high-temperature solid state method with different concentrations (between 0.5 and 2 mol%) of dopant Ho3+ emitting ions and different concentrations (between 5 and 20 mol%) of sensitizer Yb3+ ions. The dopant ions provided the material with intense luminescence emission; green emissions (centered at 542 nm from F-5(4),S-5(2) - GT I-5(8) electronic transition of Ho3+ ions) resulted upon ultraviolet excitation, and red (centered at 659 nm from F-5(5) - GT I-5(8) electronic transition of Ho3+ ions) upon near-infrared excitation. The co-doped materials were obtained under identical experimental conditions by adding Li+ ions (5, 7.5, 10, and 15 mol%). The powders co-doped with 7.5 mol% Li+ ions showed a downconversion emission intensity more than twice as high as the samples without if co-doping. In upconversion, an equal intensifica...tion of emission was achieved with co-doping with 10 mol% Li+. The influences of Ho3+/Yb3+ concentration ratio and Li+ co-doping level on emission color and emission branching was investigated and analyzed for both downconversion and upconversion emission. Increasing Yb3+ concentration was found to increase the share of dominant emission (green) in downconversion, but decreased the share of dominant emission (red) in upconversion. (C) 2015 Elsevier B.V. All rights reserved.