A series of single crystals of Eu³⁺ doped lutetium oxide, Lu_2-2xEu_2xO₃(x = 0.001, 0.002, 0.005, 0.01, 0.025 and 0.05), were grown by the floating zone method. Correlated measurements of afterglow curves, photoluminescence excitation and photoluminescence, photoluminescence decay curves and thermoluminescence curves were performed. Afterglow intensity evidently decreases above 2.5% europium doping concentration. It is discussed in the light of the influence of Eu(S₆)→Eu(C₂) energy transfer and trap states in Lu₂O₃:Eu. Thermoluminescence analysis reveals that the trap states in Lu₂O₃:Eu samples are almost the same and the afterglow difference mainly is due to the profound Eu(S₆)→Eu(C₂) energy transfer efficiency above 2.5% Eu.