Abstract
Visible to near infrared down-conversion has been studied in Tm3+/Yb3+-codoped fluorozirconate glasses, namely ZBLA (57ZrF4-34BaF2-5LaF3-4AlF3 in mol%) and ZLAG (70.2ZrF4-23.4LaF3−0.6AlF3-5.8GaF3 in mol%). Upon blue excitation at 467nm, Tm3+ doped glasses yield weak red at 650nm and strong luminescence around 800nm. With the addition of Yb3+, emission between 950 and 1100nm from the Yb3+: 2F5/2 → 2F7/2 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 ηETE was 64.5% in ZBLA glasses doped with 0.75Tm3+/10Yb3+; this efficiency was mainly limited by the strong Yb3+ to Tm3+ back energy transfer. ηETE 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+.
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