[1] [1] Sandrock T, Scheife H, Heumann E et al.. High-power continuous-wave upconversion fiber laser at room temperature. Opt. Lett., 1997, 22(11):808～810

[2] [2] Xie P, Gosnell T R. Room-temperature upconversion fiber laser tunable in the red, orange, green, and blue spectral regions. Opt. Lett., 1995, 20(9):1014～1016

[3] [3] Zou X L, Toratani H. Dynamics and mechanisms of up-conversion processes in Yb3+ sensitized Tm3+- and Ho3+-doped fluorozircoaluminate glasses. J. Non-Cryst. Solids, 1995, 181(1, 2):87～99

[4] [4] Auzel F. Materials and devices using double-pumped phosphors with energy transfer. Proc. IEEE, 1973, 61:758～786

[5] [5] Mita Y, Yamamoto H, Katayanagi K et al.. Energy transfer processes in Er3+- and Yb3+-doped infrared upconversion materials. J. Appl. Phys., 1995, 78(2):1219～1223

[7] [7] Zhang X X, Hong P, Bass M et al.. Blue upconversion with excitation into Tm ions at 780 nm in Yb- and Tm-codoped fluoride crystals. Phys. Rev. (B), 1994, 51(14):9298～9301

[8] [8] Reisfeld R, Jorgensen C K. Lasers and Excited States of Rare Earths. Berlin, Heidelberg: Springer Verlag, 1977. 169～172