Investigation of CaMoO4 single crystals with low residual absorption

Calcium molybdate enriched with the 100Mo isotope (40Ca100MoO4) is a promising material for use in cryogenic scintillation detectors. The main requirements of crystalline elements of the detector are absence of color and the attenuation coefficient (μ) not higher than 0.01cm−1 at 520nm wavelength. 40Ca100MoO4 and 40Ca100MoO4:Nb5+ single crystals have been investigated. The influence of isothermal annealing on the attenuation spectra in the 350 to 700nm wavelength range has been studied. A broad absorption band with a maximum at λ=460nm is observed in the attenuation spectra of the sample. The dichroism phenomenon which is associated with anisotropy of the color centers in the crystals is observed along directions perpendicular to the optical axis. Annealing of the enriched samples at 1250°C in an O2 atmosphere leads to a substantial reduction of the intensity of the band near 460nm. The attenuation coefficient of the 40Ca100MoO4:Nb5+ crystals meets the requirement, which is μ≪0.01cm−1 at λ=520nm. It is determined that absorption band near 460nm and dichroism are absent.