Yb3+ ion as a sensitizer for the upconversion luminescence in nanocrystalline Gd3Ga5O12:Ho3+

The effect of Yb3+ co-doping on the upconversion luminescence in nanocrystalline Gd3Ga5O12:Ho3+ was examined. Strong and efficient NIR to green anti-Stokes luminescence was noted in nanocrystalline Gd3Ga5O12:Ho3+, Yb3+ after excitation into the 2F5/2 level of Yb3+ with 978 nm radiation. Weaker blue, red and NIR anti-Stokes luminescence was also observed after 978 nm excitation. An enhancement of the red 5F5 → 5I8 luminescence was observed in the anti-Stokes spectrum compared to the Stokes emission spectrum. This enhancement was attributed to two distinct energy transfer upconversion (ETU) mechanisms which preferentially populate the (5F4, 5S2) and 5F5 levels.