Blue to NIR down-conversion in Tm3+/Yb3+-codoped fluorozirconate glasses compared to Pr3+/Yb3+ ion-pair

Visible to near infrared down-conversion has been studied in Tm3+/Yb3+-codoped fluorozirconate glasses, namely ZBLA (57ZrF(4)-34BaF(2)-5LaF(3)-4AlF(3) in mol%) and ZLAG (70.2ZrF(4)-23.4LaF(3)-0.6AlF(3)-5.8GaF(3) in mol%). Upon blue excitation at 467 nm, Tm3+ doped glasses yield weak red at 650 nm and strong luminescence around 800 nm. With the addition of Yb3+, emission between 950 and 1100 nm from the Yb3+: F-2(5/2) -> F-2(7/2) transition was observed. This emission well matched with the band gap of crystalline silicium. The mechanism responsible for down-conversion in the Tm3+/Yb3+ ion-pair is a down-shifting process. The highest energy transfer efficiency eta(ETE) was 64.5% in ZBLA glasses doped with 0.75Tm(3+)/10Yb(3+); this efficiency was mainly limited by the strong Yb3+ to Tm3+ back energy transfer. eta(ETE) appeared to increase more rapidly with the addition of Yb3+ in ZLAG glasses, as already observed for the energy transfer in Pr3+/Yb3+ ion-pair. The origin of the difference between the two hosts is probably related to the distribution of rare-earth ions in the host matrix, as shown by molecular dynamics simulation.@ The Tm3+/Yb3+ system is found much less efficient that the Pr3+/Yb3+ one, because of less efficient quantum efficiency together with lower blue absorption of Tm3+ compared to Pr3+.