© 2018 Elsevier B.V. Photoluminescence of Ce3+- and Pr3+-activated Sr2GeO4powders was measured between 17 and 600 K. For both ions strong 4fn−15dn→4fn(d-f) emission is observed at low temperatures, around 410 nm (Ce3+) and 280 nm (Pr3+). The Ce3+d-f emission quenches starting at 150 K and disappearing completely just above room temperature. Pr3+d-f luminescence shows an onset of quenching also around 150 K and disappears completely between 250 and 300 K. For Pr3+quenching of the d-f emission was connected with an increasing intensity of the3P0luminescence at first and1D2emission at even higher temperatures. Both these 4fn→4fnemissions were observed up to 600 K. Based on the similar quenching temperatures, thermally stimulated photoionization of the 5d electrons from 5d level of Ce3+or Pr3+to the conduction band is proposed as the most probable mechanism for quenching of the d-f emissions.