Enhanced upconversion multicolor and white light luminescence in SiO _2-coated lanthanide-doped GdVO_4 hydrothermal nanocrystals

摘要

Tetragonal zircon-type codoped Yb, Ln-GdVO_4 (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 SiO_2 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 Ho~(3+), Tm~(3+) and Er~(3+), 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 Gd_(0.829)Yb_(0.15)Tm_(0.01)Ho _(0.009)Er_(0.002)VO_4.