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).