F-Interstitial passivation preserves host-like optoelectronic properties in ²²⁹Th:YLF nuclear-clock platforms

Area of Science:

• Solid State Physics
• Materials Science
• Computational Chemistry

Background:

• Charge compensation is crucial for stabilizing defects in doped crystals like ²²⁹Th:LiYF₄.
• Understanding defect impact on optoelectronic properties is key for material applications.

Purpose of the Study:

• To investigate charge compensation mechanisms in ²²⁹Th:LiYF₄ using density-functional theory.
• To analyze the impact of different compensation strategies (Li-vacancy vs. F interstitial) on optoelectronic response.

Main Methods:

• Density-functional theory (DFT) calculations were employed.
• Formation energies of Li-vacancy configurations (near, mid, far) and fluorine interstitials (F_i) were compared.
• Local density of states (PDOS) and optical conductivity (ε₂(ω)) were computed, including spin-orbit coupling.

Main Results:

• The near Li-vacancy configuration showed the lowest formation energy, but F_i was energetically competitive.
• Vacancy-based compensation altered the local electrostatic field and narrowed the band gap.
• Fluorine interstitials (F_i) effectively screened the Th center, preserving a host-like band gap without midgap states.

Conclusions:

• Fluorine interstitials (F_i) represent an energetically favorable and effective charge compensation mechanism in ²²⁹Th:LiYF₄.
• The F_i route maintains the host-like optoelectronic behavior, crucial for applications utilizing the nuclear transition energy.