Multi-wavelength visible up-converted luminescence in novel heavily doped Ytterbium-Holmium silica fiber under low-power IR diode pumping

Fabrication of novel silica fiber heavily doped with ytterbium (Yb3+) and holmium (Ho3+) for the use as a potentially lasing and amplifying fiber-optic material is reported. Luminescent properties of the fiber are studied in the visible and near-IR spectral ranges under the low-power IR diode pumping. Analysis of the fiber luminescence and absorption spectra allows one to conclude that, at concentration of Ho3+ of one-order lower than that of Yb3+ (∼0.5% and ∼6%, respectively), an effective energy migration and up-conversion within the Yb3+-Ho3+ mixed system take place, leading to the visible luminescence. An avalanche-like character of the up-conversion process and possible impact of Yb3+ ion pairs' formation on an energy transfer from Yb3+ to Ho3+ are discussed