Investigation of the upconversion processes in nanocrystalline Gd3Ga5O12:Ho3+

Intense upconversion luminescence is reported for the first time in a Ho3+-doped nanocrystalline material. Anti-Stokes blue and green luminescence was noted in nanocrystalline Gd3Ga5O12:Ho3+ after excitation into the 5F5 level with 647 nm radiation. Excitation at 756 nm into the 5I4 level resulted in green and red anti-Stokes emission. In both cases, an excited state adsorption mechanism is thought responsible for the observed upconversion luminescence. The temporal dependence of the upconverted luminescence for the two excitation wavelengths revealed that the 5I7 level was the intermediate level in both two-photon processes.