The unusual temperature dependence of the Eu$^{2+}$ fluorescence lifetime in CaF$_2$ crystals

TL;DR

This paper investigates the unusual temperature dependence of Eu$^{2+}$ fluorescence lifetime in CaF$_2$ crystals, revealing a non-monotonic behavior explained by energy level simulations.

Contribution

It presents experimental measurements and a theoretical model explaining the atypical temperature dependence of Eu$^{2+}$ fluorescence lifetime.

Findings

Fluorescence lifetime increases between 100K and 300K

Lifetime decreases at temperatures below 100K and above 300K

Simulation matches experimental lifetime behavior

Abstract

Fluorescence lifetimes of Eu$^{2+}$ doped in CaF$_2$ are measured at various temperatures between 4K and 450K. The lifetime increases with between 100K and 300K, in contrast to the usual lifetime-temperature dependence. At higher or lower temperatures the lifetime decreases with increasing temperature. The phenomenon is explained by simulation of the energy levels and lifetimes of low-lying $4f^65d$ states involved in the fluorescence.