Besides the known energy levels of Eu3+ at lattice sites of symmetryC 2 in Y2O3, some transitions of this ion at lattice sites of symmetryC 3i in the same host crystal have been found and it was possible to construct the energy level scheme in part. Evidence for an energy transfer from Eu3+(C 3i ) to Eu3+(C 2) is given, the strength of which is measured as a function of the Eu2O3 concentration. The results lead to the assumption of a fixed distanceR 0 for the interaction responsible for the energy transfer. A temperature-independent value ofR 0=8.7 A was found. The full explanation of the underlying quantum mechanical mechanism requires further experiments.