Defect physics in $Yb^{3+}$-doped $CaF_2$ from first-principles calculation

TL;DR

This study uses first-principles calculations to analyze defect physics in Yb-doped CaF2, revealing how growth conditions influence defect clustering and luminescence efficiency, and providing guidelines for optimizing device performance.

Contribution

It provides the first theoretical insights into defect energetics and clustering in Yb-doped CaF2, guiding defect control for improved luminescence.

Findings

Fluorine-rich conditions promote Yb clustering.

Yb clustering enhances luminescence efficiency.

Defect energetics suggest doping strategies for defect control.

Abstract

Calcium fluoride has been widely used for light up-/down-conversion luminescence by accommodating lanthanide ions as sensitizers or activators. Especially, Yb-doped \ce{CaF2} exhibits unique defect physics, causing various effects on the luminescence. This makes it vital for high efficiency of devices to control the defect-clustering, but theoretically principal guidelines for this are rarely provided. Here we perform the first-principles study on defect physics in Yb-doped \ce{CaF2} to reveal the thermodynamic transition levels and formation energies of possible defects. We suggest that the fluorine rich growth condition can play a key role in enhancing the luminescence efficiency by facilitating the Yb-clustering and suppressing the defect quenchers in bulk. Detailed energetics of defect aggregation not only well explains the experimentally favored Yb-clustering but also presents $n$- or $p$-type doping method for the cluster control.