Visible and near infrared up-conversion luminescence in Yb3+/Tm3+ co-doped yttria-alumino-silicate glass based optical fibers

We report blue light up-conversion (UC) emission in Yb-Tm co-doped nano-phase separated yttria-alumino-silicate (YAS) glass based D-shaped with low-index cladding optical fibers. Y2O3 creates an environment of nano structured YAS glass phases with Yb and Tm rich zone into the core glass which confirmed from TEM analyses. This kind of glass host assists in distributing of Yb and Tm rich zone uniformly throughout the core region. Yb and Tm doped regions exist mainly into nano YAS phases, defined as RE rich nano YAS-RE phases. All samples exhibit UC luminescence peaks at 483 nm, 650 nm and 817 nm for Tm3+ and 1044 nm for Yb3+ under excitation by 975 nm laser light. In such type of nano-engineered glass-ceramic based host, almost all the Yb ions transferred its energy to the nearer Tm ions. In particular 483 nm emission is attributed to 1G4→3H6 transition through a three step resonance energy transfer (ET) from excited Yb3+. The highest emission intensity is obtained with a concentration of 0.5 wt% Tm3+ and 2.0 wt% Yb3+. The ET between Yb3+ and Tm3+ is increased with increase of Yb3+ concentration with respect to Tm3+. The experimental fluorescence life-times of Tm3+ upconversion emission at visible wavelengths into such kind of fiber is reported under 975 nm pump excitation. The present study is important for development of an efficient tunable 483 nm fluorescence light source.