M. Kochanowicz, W. Mazerski, J. Żmojda, K. Czajkowski, and D. Dorosz, “Green upconversion emission in tellurite optical fibre codoped with Yb3+/Er3+”, Photonics Lett. Pol., vol. 5, no. 1, pp. pp. 35–37, Mar. 2013.