Yb3+-sensitized, Ln3+(Er3+, Pr3+)-doped Y6O5F8 micron-sized bundles of highly crystalline individual nanotubes have been prepared through hydrothermal syntheses at 185 ºC. The inhomogeneous broadening observed in their optical spectra is associated to the large distribution of crystal fields around Y3+(Ln3+) sites in the orthorhombic Pbcm Vernier-type Y6O5F8 host. Based on ratiometric analyses of the thermal evolution of intensities of near-infrared NIR (~978 nm)-excited green upconversion emissions corresponding to 2H11/2, 4S3/2→4I15/2 Er3+ transition, the temperature sensing behaviour of Er, Yb:Y6O5F8 was studied. This thermal sensor exhibits a very high sensitivity S = 0.0060 K-1 at physiological temperatures, that surpasses the S value found for Er, Yb:-NaYF4 at these temperatures, and a maximum S = 0.0082 K-1 at  500 K. Also under NIR diode laser excitation, the color of the upconverted light from codoped Pr, Er, Yb:Y6O5F8 nanotubes can be selected by the control of the Pr3+ concentration and by the excitation regime and power density. Samples with low Pr3+ concentration emit green light, and the selection between bluish-green light and white light has been demonstrated with large Pr3+ concentration (2 mol%), under pulsed or continuous wave excitation, respectively.