A Comparison of Photoluminescence and Decay Time for LYSO:Ce Crystals at 22, -35 and -60 °C

Bright and fast LYSO:Ce crystals with SiPM readout are used for the barrel timing layer of the CMS MIP timing detector project at the HL-LHC. A thermal electric cooler is mounted on SiPMs to mitigate the expected high dark counting rate. The SiPM temperature will be controlled at -35 °C (238 K) during beam on to reduce the dark counting rate, and at a high temperature, such as 25 °C (298 K) during beam off to facilitate thermal annealing. We report photo-luminescence spectra measured at 213, 238, and 295 K for four LYSO bars from different vendors. No significant variation in both intensity and decay time was observed. The results demonstrate that LYSO:Ce crystals work well down to -60 °C.