This work reports on the structural characterization and on the low-temperature upconversion spectroscopy of the ${\mathrm{Y}}_2{\mathrm{O}}_3:2\%\mathrm{Er},1\%\mathrm{Yb}$ nanophosphor prepared by thermal decomposition of a polymeric resin (Pechini’s method [U.S. Patent No. 3,330,697 (July 11 1967)]). The average particle size evaluated from transmission electron microscopy lies in the range of $05–25\mathrm{nm}$ . The high-resolution upconversion luminescence spectrum at $10\mathrm{K}$ in the ultraviolet to near infrared (UV-NIR) spectral regions shows narrow lines, characteristic of ${\mathrm{Er}}^{3+}$ transitions occupying both ${\mathrm{Y}}^{3+}$ sites with point symmetries $C_2$ and $C_{3i}$ in the oxide cubic system. The excitation spectrum at $10\mathrm{K}$ in the IR region was used to monitor the green upconversion and IR luminescences and it displayed Er and Yb lines. Power dependence measurements at 298 and $10\mathrm{K}$ indicate that the main upconversion mechanism is a two-photon excitation process. The temperature dependence of the upconversion luminescence shows a decrease in the emission intensity with increasing temperature, and such decrease is much more evident for the emission in the violet than in the green and the red regions.