Low temperature luminescence and scintillation properties of NaLa(MoO4)2 crystal grown by the vertical Bridgman method

Abstract

Scheelite related rare-earth double molybdate with the formula of NaLa(MoO4)2 is a promising scintillator for investigating the neutrinoless double beta decay process. In this study, NaLa(MoO4)2 crystal was grown by the vertical Bridgman method using spontaneous crystallization. The as-grown NaLa(MoO4)2 crystal exhibited yellow and dark blue in color (from top to the bottom). The powder x-ray diffraction and optical transmission spectra of the crystal were measured at room temperature. The temperature dependence of the luminescence and scintillation properties were measured under the excitations of 4.42 eV UV light from a LED source and β-particles from a90Sr source in 10–300 K range, respectively. The transmittance of the annealed NaLa(MoO4)2 crystal sample with the thickness of 10 mm was about 65–72% above the fundamental absorption edge. The light yield under UV and β-particles excitations were found to be enhanced upon cooling and exhibited maximum intensity at 10 K. The luminescence light yield of NaLa(MoO4)2 crystal was estimated to be about half of that of CaMoO4 crystal and 18 times as much as that of Li2MoO4 crystal at 10 K. The scintillation light yield of NaLa(MoO4)2 crystal reached the maximum at 10 K and was 70% of Li2MoO4 crystal. The shortest average decay time of 6.12 μs was obtained at 250 K, which was further slowed down upon cooling of the crystal and the longest average decay time of 442.77 μs was found to be at 10 K. Considering the possibility of crystal growth with large volume and high quality, the luminescence and scintillation properties of NaLa(MoO4)2 crystal revealed that this scintillation material may be a promising candidate as a cryogenic detector for investigating the neutrinoless double beta decay (0νββ) search.