Growth and Optical Properties of a Cs₂Mo₂O₇ Single Crystal

A Cs₂Mo₂O₇ single crystal, a molybdenum-based crystal as research and development scintillation material for future neutrinoless double beta decay experiments under milli-Kelvin temperatures, was grown by the Czochralski method. The grown crystal was prepared as a sample for measurements of its optical properties. The sample was cooled down from room temperature to 10 K, and temperature dependence of emission spectrum and decay time were measured. We used a light emitting diode as an excitation source for the emission spectra measurements and a pulsed-type laser for the decay time due to its high intensity. The intensity of emission spectrum and the decay time increased as the temperature decreased. We estimated the optical energy bandgap via a transmittance measurement at room temperature. As far as we know, it is the first time to grow a large Cs₂Mo₂O₇ crystal and to study its luminescence properties. Moreover, we grew a well-studied Li₂MoO₄ crystal as a reference to compare the light output of the Cs₂Mo₂O₇ at 10 K. Through these results, the Cs₂Mo₂O₇ crystal found to be a candidate scintillator for the future neutrinoless double beta decay experiments.