Influence of Annealing on the Optical and Scintillation Properties of CaWO${}_4$ Single Crystals

Abstract

We investigate the influence of oxygen annealing on the room temperature optical and scintillation properties of CaWO${}_4$ single crystals that are being produced for direct Dark Matter search experiments. The applied annealing procedure reduces the absorption coefficient at the peak position of the scintillation spectrum ($\sim 430$ nm) by a factor of $\sim 6$ and leads to an even larger reduction of the scattering coefficient. Furthermore, the annealing has no significant influence on the \emph{intrinsic} light yield. An additional absorption occurring at $\sim 400$ nm suggests the formation of O${}^{-}$ hole centers. Light-yield measurements at room temperature where one crystal surface was mechanically roughened showed an increase of the \emph{measured} light yield by $\sim 40$ and an improvement of the energy resolution at 59.5 keV by $\sim 12$ for the annealed crystal. We ascribe this result to the reduction of the absorption coefficient while the surface roughening is needed to compensate for the also observed reduction of the scattering coefficient after annealing.

References in corpus (2)

• Results from 730 kg days of the CRESST-II Dark Matter Search
• Electron performance measurements with the ATLAS detector using the 2010 LHC proton-proton collision data

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• Precision Multi-Mode Microwave Spectroscopy of Paramagnetic and Rare-Earth Ion Spin Defects in Single Crystal Calcium Tungstate