Scintillation and Optical Characterization of CsCuI Single Crystals from 10 to 400 K.

Currently only Eu-based scintillators have approached the light yield needed to improve the 2% energy resolution at 662 keV of LaBr:Ce,Sr. Their major limitation, however, is the significant self-absorption due to Eu. CsCuI is an interesting new small band gap scintillator. It is nonhygroscopic and nontoxic, melts congruently, and has an extremely low afterglow, a density of 5.01 g/cm, and an effective atomic number of 50.6. It shows self-trapped exciton emission at room temperature. The large Stokes shift of this emission ensures that this material is not sensitive to self-absorption, tackling one of the major problems of Eu-based scintillators. An avalanche photo diode, whose optimal detection efficiency matches the 570 nm mean emission wavelength of CsCuI, was used to measure pulse height spectra. From the latter, a light yield of 36 000 photons/MeV and energy resolution of 4.82% were obtained. The scintillation proportionality of CsCuI was found to be on par with that of SrI:Eu. Based on temperature-dependent emission and decay measurements, it was demonstrated that CsCuI emission is already about 50% quenched at room temperature. Using temperature-dependent pulse height measurements, it is shown that the light yield can be increased up to 60 000 photons/MeV by cooling to 200 K, experimentally demonstrating the scintillation potential of CsCuI. Below this temperature, the light yield starts to decrease, which can be linked to the unusually large increase in the band gap energy of CsCuI.