We have demonstrated that the population feeding from the I11/24 level to the 1.5 μm fluorescence emitting I13/24 level of Er3+ ions in low phonon energy glass hosts can be enhanced by codoping with Ce3+ under optical pumping at 980 nm. The nonradiative energy transfer Er3+: 4I11/2; Ce3+: 2F5/2→Er3+: 4I13/2; Ce3+: 2F7/2, occurs in the form of phonon-assisted energy transfer, and therefore the feeding rates are faster in the tellurite glasses, which have a comparatively higher phonon energy than in the sulfide glasses. The cross-relaxation process for I13/24: 4I13/2→4I15/2: 4I9/2, which lowers the population density of the I13/24 manifold and causes a deleterious effect in the 1.5 μm fluorescence intensity, is more severe in the sulfide glasses. Population feeding rate from the I11/24 to the I13/24 level is significantly enhanced by way of cerium codoping into tellurite glasses, which promises an efficient 980 nm pumped broadband Er3+-doped fiber amplifier.
The photoluminescence behavior of (Y 1Ϫx Tb x )PO 4 phosphor was investigated by measuring emission and excitation spectra, and decay curves. The relative emission intensity and the decay time have been monitored as a function of Tb 3ϩ concentration for both 5 D 4 Ϫ 7 F j and 5 D 3 Ϫ 7 F j transitions. The decay behavior of 5 D 3 -7 F j transition, for which well known cross-relaxation has been accepted as a main factor, was analyzed by direct quenching mechanism on the basis of dipole-dipole interaction. It is, however, impossible to characterize the 5 D 4 Ϫ 7 F j transition using the direct quenching scheme. In fact, the decay curves of 5 D 4 Ϫ 7 F j transition could be analyzed by intercenter energy migration. Another type of cross-relaxation was suggested to explain the quenching of 5 D 4 Ϫ 7 F j transition.
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