Scintillating and optical spectroscopy of Al2O3:Ti for dark matter searches

In order to optimize sapphire as a cryogenic scintillation-phonon detector for dark matter, Al2O3:Ti crystals with different concentrations of doping have been studied using continuous X-ray excitation in the 30-300 K temperature range. Light yields vary by 20% for Ti concentrations between 10 and 1000 ppm at room temperature; they roughly double as the crystals are cooled from room temperature to 45 K. From the analysis of the change in the X-ray luminescence spectra of Al2O3 with the concentration of Ti, it is concluded that the well-known blue emission of Ti-doped Al2O3 is due to the radiative decay of F-centers. Recommendations are given for improving the performance of Al2O3 scintillators.