The concentration and temperature dependences of the blue luminescence intensity of the Tm3+ ion in yttrium oxide under UV and IR excitation have been measured. We made a proposal that the main role in the formation of these dependences is played by the interionic cross relaxation of excited states of Tm3+; the presence of admixed secondary rare‐earth ions can strongly influence the shape of the temperature dependence of the anti‐Stokes luminescence intensity, displacing the position of its maximum. It is shown that the quenching action of admixtures under Stokes and anti‐Stokes excitation shows up differently because of the differences in the mechanisms of population of the luminescent level.