Scintillation properties of Bi4Ge3O12 down to 3 K under γ rays

Bismuth germanate (BGO) has been widely used as a room-temperature scintillator in many applications for decades. Interest in it has recently increased as a low-temperature scintillator to be used in bolometers for rare-event detection. We present our time-resolved-scintillation studies of BGO down to 3 K under gamma-ray excitation. Our multiple-photon-counting-coincidence-based setup allows clear identification of gamma-line energies at least as low as 122 keV down to base temperature and the measurement of the light yield and decay-time constants as a function of temperature. We also discuss the time structure of the pulses and report a previously unappreciated but significant, very slow component assigned to afterglow. Finally, we demonstrate that nonlinearity of the light yield as a function of energy persists at low temperatures.