Mn2 +-sensitized near-IR emission from Nd3 +-activated Sr,Mn-metaphosphate glasses

We report on photoluminescence down-shifting and near-IR emission from Nd3 + centers in 50P2O5–(50-x)SrO–xMnO metaphosphate glasses. In those glasses, manganese exists predominantly in its divalent state with a Mn3 + fraction of less than 0.1 % of total Mn. The Mn2 + ions are octahedrally coordinated so that a broad red emission band is observed after blue excitation. The emission peak red-shifts from 680 to 743 nm, the lifetime decreases from 14.5 to 1.7 ms and the internal quantum efficiency decreases from 36.5% to 2.5% with increasing Mn2 + concentration due to concentration quenching, but luminescence activity can still be observed in the pure manganese metaphosphate. The absorption bands of Mn2 + cover the broad region from 300 to 550 nm, which allows for the sensitization of Nd3 +. Energy transfer from Mn2 + to Nd3 + occurs through a multi-phonon assisted non-radiative down-shifting energy transfer process. A decrease of the emission intensity and lifetime for VIMn2 + is observed after doping with Nd3 + giving evidence for the energy transfer. A value of 89% is estimated for the maximum energy transfer efficiency.