Concentration dependence of visible up-conversion luminescence in the laser crystal Gd3Ga5O12 doped with erbium

The concentration dependence of the near infrared to visible up-conversion (anti-Stokes) luminescence was investigated in the laser crystal Gd3Ga5O12 (GGG) doped with Er ions at three different concentrations, 1%, 10% and 30%. We found that when the crystals were pumped by an infrared (790 nm) diode laser, both the red and green up-conversion luminescence become much stronger with increasing Er concentration: the red emission becomes stronger by a greater factor. In fact, the red up-conversion luminescence was found to be weak in the 1%-Er-doped GGG and strong in the 30%-Er-doped GGG. The down-conversion (Stokes) luminescence shown by these crystals, when pumped by a blue argon laser, was also investigated and compared with the up-conversion luminescence. We believe that the main mechanism responsible for the up-conversion in Er-doped GGG is of the Energy Transfer Up-conversion (ETU) type, especially in 10% and 30%-Er-doped GGG. (C) 2000 Elsevier Science B.V. All rights reserved.