Transient photoluminescence enhancement as a probe of the structure of impurity-trapped excitons in CaF$_2$:Yb$^{2+}$

TL;DR

This paper introduces a method to directly measure impurity-trapped exciton energy levels in CaF$_2$:Yb$^{2+}$ using transient photoluminescence enhancement, revealing detailed electronic state information.

Contribution

It provides the first direct measurement of impurity-trapped exciton energy levels in CaF$_2$:Yb$^{2+}$, utilizing a novel two-step excitation technique.

Findings

Identification of sharp transitions from localized electron states

Detection of broad bands from delocalized electron state changes

Observation of trap liberation-related broad bands

Abstract

We demonstrate a direct measurement of the energy levels of impurity-trapped excitons in CaF$_2$:Yb$^{2+}$. The radically different radiative decay rates of the lowest exciton state and higher excited states enable the generation of a transient photoluminescence enhancement measured via a two-step excitation process. We observe sharp transitions arising from changes of state of localized electrons, broad bands associated with changes of state of delocalized electrons, and broad bands arising from trap liberation.