The conversion of the energy absorbed by cubic Gd_2O_3 nanocrystals doped with Er^3+ and codoped with Yb^3+ and Zn^2+ 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 Gd^3+ ions or the matrix towards the Er^3+ ions. The population of upper excited states in the Er^3+ 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 Zn^2+ ions. The temperature dependences of the upconversion luminescence yield for emission lines of 560 and 660 nm are found to be different.