Th4+ ion cluster structures and electric field gradients in 229Th:CaF2
Abstract
The low-energy nuclear isomeric transition of 229Th is a promising frequency reference for a solid-state nuclear optical clock. Wide-band-gap fluoride crystals such as CaF2 offer transparent hosts for embedding Th nuclei at high density. Substitution of Th4+ for Ca2+ requires charge compensation, linking the local defect structure to nuclear quadrupole splitting. We use first-principles calculations to examine neutral Th dimers compensated by four interstitial F ions (Fi−). Screening different compensation geometries by their relative formation energies identifies a family of low-energy configurations with closely similar local structures. These configurations share large electric field gradients and small asymmetry parameters, consistent with the experimental high-EFG site 3. Their calculated quadrupole splittings are further compared with the measured C13 spectra. Together, the energetic and spectroscopic results support Fi−-compensated Th dimers as candidate microscopic structures for site 3 in Th:CaF2.
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BibTeX
@misc{li2026cluster,
title = {{Th$^4+$ ion cluster structures and electric field gradients in $^229$Th:CaF$_2$}},
author = {Yuxiang Li and Lin Li and Qiaorui Gong and Shanming Li and Chengchun Zhao and Lu Deng and Peixiong Zhang and Yin Hang and Longsheng Ma and Shining Zhu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.39288},
eprint = {2610.39288},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.39288},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Th^4+ ion cluster structures and electric field gradients in ^229Th:CaF_2
AU - Yuxiang Li
AU - Lin Li
AU - Qiaorui Gong
AU - Shanming Li
AU - Chengchun Zhao
AU - Lu Deng
AU - Peixiong Zhang
AU - Yin Hang
AU - Longsheng Ma
AU - Shining Zhu
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.39288
UR - https://arxiv.org/abs/2610.39288
AB - The low-energy nuclear isomeric transition of ^229Th is a promising frequency reference for a solid-state nuclear optical clock. Wide-band-gap fluoride crystals such as CaF_2 offer transparent hosts for embedding Th nuclei at high density. Substitution of Th^4+ for Ca^2+ requires charge compensation, linking the local defect structure to nuclear quadrupole splitting. We use first-principles calculations to examine neutral Th dimers compensated by four interstitial F ions (F_i^−). Screening different compensation geometries by their relative formation energies identifies a family of low-energy configurations with closely similar local structures. These configurations share large electric field gradients and small asymmetry parameters, consistent with the experimental high-EFG site 3. Their calculated quadrupole splittings are further compared with the measured C13 spectra. Together, the energetic and spectroscopic results support F_i^−-compensated Th dimers as candidate microscopic structures for site 3 in Th:CaF_2.
ER -