**Acknowledgements**

The author sincerely acknowledges the following people, contributing in the researches highlighted above: Dr. N.S. Kozlova (National University of Science and Technology (MISIS), Moscow, Russia)—for assistance in electron irradiation of all fibers; Drs. M.C. Paul and S. Ghosh (Central Glass & Ceramic Research Institute, Kolkata, India)—for providing samples of Ce and Ce(Au)-doped fibers and for discussions; Drs. V.V. Dvoyrin, V.M. Mashinsky, and E.M. Dianov (Fiber Optics Research Center of the Russian Academy of Sciences, Moscow, Russia)—for providing samples of Bi-doped fibers and valuable discussions; Dr. Yu.O. Barmenkov (Centro de Investigaciones en Optica, Leon, Mexico)—for participating in experi‐ ments with Ce and Ce(Au)-doped fibers and useful discussions. The author also thanks support from the Ministry of Education and Science of the Russian Federation under the "Increase Competitiveness Program of NUST «MISiS»" (Grant К3-2015-056).
