Intense green upconversion emission in Tb3+/Yb3+ codoped alumino-germano-silicate optical fibers

We observed intense green upconversion emission from Tb3+ centered at 546 nm due to transition D-5(4) --> F-7(5) in Tb3+/Yb3+ codoped alumino-germano-silicate optical fibers by direct excitation of Yb3+ ions with a laser diode at 976 nm. A two-photon cooperative energy transfer upconversion among a pair of Yb3+ donor ions and a Tb3+ acceptor ion are responsible for the observed green emission. Appropriately increasing the concentration of Tb3+ relative to Yb3+ was found to facilitate the energy transfer upconversion process from Yb3+ to Tb3+, while an excess of Tb3+ ions inversely introduced more of the concentration quenching effect and phonon-assistant backward energy transfer from Tb3+ to Yb3+ and, therefore, damaged the observed green emission. The intensity of the observed green emission was found optimum for a concentration ratio of Tb3+ to Yb3+ of 2 : 1 in alumino-germano-silicate optical glass fibers. (C) 2010 Optical Society of America