Decay curves of Ho3+. For (a) 5 F3 → 5I8, (b) 5 F4, 5S2 → 5I8, and (c) 5 F5 → 5I8 emissions under excitation of 450 nm. The inset shows the average decay lifetime and energy transfer efficiency as a function of Yb3+ doping concentration. (d) Energy level diagram of Ho3+ and Yb3+ showing mechanisms for NIR QC processes.
Guo et al. Nanoscale Research Letters 2012 7:636 doi:10.1186/1556-276X-7-636