Strong blue upconversion emission has been observed from Y2O3:Tm3+ phosphors under 632.8-nm excitation, in addition to weaker green and red emissions. All of these emissions, including the red, showed a two-photon intensity dependence on the incident 632.8-nm laser power. The emissions that showed only a one-photon intensity dependence occurred in the near-IR region of the spectrum. The mechanism for the origins of these emissions was derived from temperature studies over the range of 0 to - 190 degreesC and their dependence on the laser power at room temperature. Energy values are derived for all of the Tm3+ levels in the cubic Y2O3 lattice between the H-3(6) ground state and the D-1(2) excited state at ca. 27 500 cm(-1) from the positions of the emission bands.