Measurements of the band gap of ThF4 by electron spectroscopy techniques

We present an experimental determination of the band gap of ThF4 performed by two different techniques. The first measurement was performed by combining x-ray photoemission spectroscopy and bremsstrahlung isochromat spectroscopy. The second measurement exploited the position of the inelastic threshold in reflection electron energy loss spectroscopy. Both measurements gave compatible values of the band gap, with the average E = 10.2(2) eV. This value was found to be in excellent agreement with theoretical calculations. The measured band gap is significantly larger than the 229mTh excitation energy, making ThF4 a possible candidate material for a solid-state nuclear clock based on the vacuum ultraviolet γ decay.