dx.doi.org/10.1063/1.1565697
J. Appl. Phys.
Photonic Materials

Kik, P.G, & Polman, A. (2003). Cooperative upconversion as the gain-limiting factor in Er doped miniature Al2O3 optical waveguide amplifiers. J. Appl. Phys., 93, 5008–5012. doi:10.1063/1.1565697