Spectroscopic investigations of Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+ co-doped germanate glasses and optical fibers. - Marcin Kochanowicz; Jacek M. Zmojda; Piotr Miluski; P. Jelen; Maciej Sitarz; Dominik Dorosz (ICTON, 2016)