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

We observed intense green upconversion emission from Tb(3+) centered at 546 nm due to transition D(4)5-->F(5)7 in Tb(3+)/Yb(3+) codoped alumino-germano-silicate optical fibers by direct excitation of Yb(3+) ions with a laser diode at 976 nm. A two-photon cooperative energy transfer upconversion among a pair of Yb(3+) donor ions and a Tb(3+) acceptor ion are responsible for the observed green emission. Appropriately increasing the concentration of Tb(3+) relative to Yb(3+) was found to facilitate the energy transfer upconversion process from Yb(3+) to Tb(3+), while an excess of Tb(3+) ions inversely introduced more of the concentration quenching effect and phonon-assistant backward energy transfer from Tb(3+) to Yb(3+) and, therefore, damaged the observed green emission. The intensity of the observed green emission was found optimum for a concentration ratio of Tb(3+) to Yb(3+) of 2:1 in alumino-germano-silicate optical glass fibers.