Zheng, C.B., Xia, Y.Q., Qin, F., Yu, Y., Miao, J.P., Zhang, Z.G. and Cao, W.W. (2010) Femtosecond Pulsed Laser Induced Synthesis of Ultrafine Y2O3: Pr3+, Yb3+ Nanoparticles with Improved Upconversion Efficiency. Chemical Physics Letters, 496, 316-320.