Upconversion Luminescence Transients

Inhomogeneous active-ion distributions in laser materials lead to strong deviations of upconversion versus direct luminescence transients from the quadratic law of energy-transfer upconversion. Measured luminescence decay curves in $LaSc_{3}(BO_{3})_{4}:Nd^{3+}$ and $GdVO_{4}:Nd^{3+}$ confirm experimentally the predicted deviations. Differences in energy migration within the metastable level of $Nd^{3+}$ are indentified.