Delayed stimulated afterglow from holmium ions in crystals with coactivators

Delayed stimulated afterglow from holmium ions in $\alpha\beta-SrF_2-YF_3$ crystals was observed and investigated. This took the form of several series of emission spikes separated by dark intervals after the action of a single pump pulse. The effect is attributed to some features of the mechanism for population of the upper active level of the lasing holmium ion in the presence of sensitizer ions. It is found that in order to observe the effect, the system must incorporate a metastable level from which energy transfer to the active level provides an independent “additional pumping” system for the holmium ions acting over times much longer than the pump pulse duration.