Thorium‐Doped Lithium Fluoride Single Crystal: A Potential Promising Candidate for Solid State Nuclear Optical Clock Materials

Abstract

AbstractThe solid‐state nuclear optical clock based on 229Th‐doped crystal has great advantages in frequency stability, excitation and detection of nuclear transition, miniaturization, commercialization, and spaceborne ability of nuclear optical clock. Here, the potential of LiF crystal as a host for Th ions is predicted by theoretical calculation, and on this basis, the Th:LiF crystal is successfully grown experimentally for the first time. The theoretical results demonstrate that although the challenges of charge nonconservation and ion radius mismatch between Li+ and Th4+ ions exist, effective doping of thorium can still be achieved via energetically favorable charge compensation mechanisms in an F‐rich environment, and the transmittance of Th:LiF crystal in nuclear transition band will only have a slight decrease, smaller than that of pure LiF crystal. The experimental results prove that the doping concentration of Th:LiF crystal can reach about 8.3 × 1018 cm−3 and the transmittances of 1 mm thick Th:LiF and pure LiF crystal samples grown in similar conditions are ≈68% and 72% at 152.7 nm, respectively. The Th:LiF crystal with high doping concentration, high transmittance, and low background luminescence is expected to be a promising candidate for solid‐state nuclear optical clock materials.