INFLUENCE OF TEMPERATURE ON INFRARED TO VISIBLE CONVERSION IN TELLURITE GLASS DOPED WITH ERBIUM AND YTTERBIUM

The process contributing to the stepwise excitation of visible luminescence in tellurite glass doped with erbium and ytterbium have been studied experimentally in the 300-500 K temperature region and interpreted using a rate equation model. The Stokes' shift between excited levels of donors and acceptors involved in energy transfer is negligibly small in this matrix, excitation energy is transferred in both directions and the determination of donor-acceptor transfer rates is difficult. Analysis of the time dependence of infrared excited visible luminescence indicates that the rates of energy transfer from Yb3+ to Er3+ are large compared to intrinsic decay rates of donors and acceptors for donor concentrations of about 2 x 10(21) ions cm-3. When the donor concentration is lowered to 1.3 x 10(21) ion cm-3 this relation is no longer valid. The tellurite glass doped with erbium and ytterbium may be an interesting material for the i.r. visible conversion experiments at high temperatures, provided the donor concentration is kept low.