Electronic Structure and optical properties of Th doped MgF₂

The Thorium isotope 229Th features a long-lived isomer state, 229mTh, which lies extremely close to the ground state at 7.8 eV. It is therefore proposed to be used as an atomic clock with extraordinary precision. Additionally, it might be used in studies of material properties by means of Mössbauer spectroscopy and it may be used for building a laser.
Due to the scarcity of the material and the large density needed, it is suggested to be doped into a crystal. As a host crystal we investigated MgF2, that shows a band gap of 10.8 eV, with ab-initio calculations performed in VASP. It is shown that Th occupies a Mg site but considering that Th and Mg have a different valence of 4+ and 2+ respectively, two compensation charges must be present. We examined different possibilities for the atoms and positions of the compensation charges to determine if the band gap stays larger than the energy of 229mTh. The results presented include a comparison of the compensations investigated with their respective band gap.