Search for New Molybdenum-Based Crystal Scintillators for the Neutrino-Less Double Beta Decay Search Experiment

Studies of Li₂O–MoO₃, Cs₂MoO₄–MoO₃, and Na₂O–MoO₃ phases have helped us to develop several new crystals such as Li₂MoO₄, Li₄Mo₅O₁₇, Li₂Mo₄O₁₃ Cs₂MoO₄, Cs₂Mo₂O₇, Cs₂Mo₃O₁₀ Na₂Mo₂O₇, and Na₆Mo₁₁O₃₆ grown by a Czochralski method. Syntheses of the polycrystalline materials are discussed based on the thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) analysis and the crystals’ structures are reported based on the X-ray powder diffraction (XRD) analysis. Luminescence properties of the crystals from room temperature to 10 K are studied by exciting the crystal with a 280 nm light emitting diode (LED). The scintillation light yields of the crystals at different low temperatures are studied by exciting the crystal with strontium-90 (⁹⁰Sr) beta source. The developed crystals are not luminescent at room temperature. At cryogenic temperature, however, they become luminescent with longer decay times. This work also reports on the luminescence and scintillation properties of ZnMoO₄, PbMoO₄, Pb₂MoO₅, and CaMoO₄ crystals which have been grown at other institutes. The newly developed crystals’ results are compared with the result of a standard CaMoO₄ crystal. Among the new Mo-based crystals, the Na₂Mo₂O₇ crystal shows the most promising properties for the neutrino-less double beta decay (0νββ) search experiments at cryogenic temperature.