Temperature dependence of 4fn−15d1→4fn luminescence of Ce3+ and Pr3+ ions in Sr2GeO4 host

Photoluminescence of Ce3+- and Pr3+-activated Sr2GeO4 powders 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 the 3P0 luminescence at first and 1D2 emission at even higher temperatures. Both these 4fn→4fn emissions 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.