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.
@article{arxiv.1909.02397,
title = {Defect physics in $Yb^{3+}$-doped $CaF_2$ from first-principles calculation},
author = {Yun-Hyok Kye and Chol-Jun Yu and Un-Gi Jong and Chol-Nam Sin and Weiping Qin},
journal= {arXiv preprint arXiv:1909.02397},
year = {2019}
}