Intensity of the bands of upconversion luminescence of β-NaYF4 : Yb3+/Tm3+ nanopowders in DMSO suspensions vs intensity of exciting radiation were analyzed. Ranges of changes in the intensity of excitation have been established, in which either the processes of energy transfer from the sensitizer ion to the activator ion or the decay of intermediate levels of activator ions dominate. Keywords: rare earth ions, upconversion luminescence, nanoparticle suspensions, sensitizer, activator.