Progresses on Th-doped materials for solid-state nuclear clock

The isomeric transition of thorium-229 (²²⁹Th), as the only known laser-accessible nuclear transition, offers the possibility for the development of a new generation of optical clocks. Solid-state nuclear optical clock based on ²²⁹Th-doped crystals or thin films has attracted much attention due to its potential advantages in high stability, miniaturization, and robustness. This paper reviews the research progress of solid-state nuclear optical clock materials, analyzes the preparation, defects, and properties of the candidate solid material systems for ²²⁹Th, explores the influence of the local crystal environment on the nuclear transition, focuses on introducing the latest research results of crystal materials such as Th-doped CaF₂ and LiSrAlF₆, and looks forward to the future development direction of this field. It could provide a reference for the material selection and optimization of solid-state nuclear optical clocks.