Abstract
Tetragonal zircon-type codoped Yb, Ln–GdVO4 (Ln=Tm, Ho, Er) upconverting nanocrystals with square and rectangular sections were prepared through an efficient low-temperature hydrothermal synthesis. Further processing that combined annealing at 600 °C followed by coating of the surface with a uniform 5 nm-shell of SiO2 resulted in a significant improvement of the intensity of the upconverted emitted visible light following near-infrared (∼980 nm) diode laser excitation with respect to raw hydrothermal nanocrystals. Strong tunable color and bright visible light composed of red–green, blue and green emissions from Ho3+, Tm3+ and Er3+, respectively, were generated by adjusting the Yb–Ln composition of these silica-coated nanocrystals. Based on calculations of CIE color coordinates, nearly ideal white upconversion light was achieved for samples of composition Gd0.829Yb0.15Tm0.01Ho0.009Er0.002VO4.
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