The conversion of the energy absorbed by cubic Gd2O3 nanocrystals doped with Er3+ and codoped with Yb3+ and Zn2+ ions in a temperature range of 95–425 K is studied at various concentrations of dopants. The photoluminescence spectra confirm the ability of excitation energy transfer from the Gd3+ ions or the matrix towards the Er3+ ions. The population of upper excited states in the Er3+ ions depends on the way of excitation, which cause the alterations in the probability of multiphonon relaxation from the excited states to the radiative levels. The kinetics of photoluminescence decay exhibit the possible energy transfer from anionic defects created by extra doping with Zn2+ ions. The temperature dependences of the upconversion luminescence yield for emission lines of 560 and 660 nm are found to be different.