1. Godlewski M, Gryczynski I, Tomsia K, et al. Fluorescence upconversion in Sm-doped Gd2O3. Appl Phys Lett, 2006, 88: 011906-1–3
2. Beurer E, Grimm J, Gerner P, et al. New type of near-infrared to visible photon upconversion in Tm2+-doped CsCaI3. J Am Chem Soc, 2006, 128(10): 3110–3111
3. De la Posa E, Salas P, Desirena H, et al. Strong green upconversion emission in ZrO2:Yb3+-Ho3+ nanocrystals. Appl Phys Lett, 2005, 87: 241912-1–3
4. Dong B, Liu D P, Wang X J, et al. Optical thermometry through infrared excited green upconversion emissions in Er3+-Yb3+ codoped Al2O3. Appl Phys Lett, 2007, 90: 181117-1–3
5. Silver J, Martinez-Rubio M I, Ireland T G, et al. The effect of particle morphology and crystallite size on the upconversion luminescence properties of erbium and ytterbium co-doped yttrium oxide phosphors. J Phys Chem B, 2001, 105(5): 948–953