Temporal dynamics of the frequency non-degenerate transient photoluminescence enhancement observed following excitation of inter-configurational f→d transitions in CaF2:Yb2+

We present a detailed investigation of the dynamics of impurity-trapped excitons in CaF2:Yb2+ using transient photoluminescence enhancement induced via a two-frequency, sequential excitation process employing a UV optical parametric amplifier (OPA) synchronized to an infrared free electron laser (FEL). The temporal behaviour is well approximated by a multi-level rate equation model as relaxation between excited states of the exciton as well as a small contribution from local lattice heating by the FEL which becomes evident due to the 40 cm−1 splitting of the exciton excited states giving rise to the transient photoluminescence enhancement itself.