Scintillation and Optical Characterization of CsCu₂I₃ Single Crystals from 10 to 400 K

Currently only Eu²⁺-based scintillators have approached the light yield needed to improve the 2% energy resolution at 662 keV of LaBr₃:Ce³⁺,Sr²⁺. Their major limitation, however, is the significant self-absorption due to Eu²⁺. CsCu₂I₃ 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/cm³, 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 Eu²⁺-based scintillators. An avalanche photo diode, whose optimal detection efficiency matches the 570 nm mean emission wavelength of CsCu₂I₃, 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 CsCu₂I₃ was found to be on par with that of SrI₂:Eu²⁺. Based on temperature-dependent emission and decay measurements, it was demonstrated that CsCu₂I₃ 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 CsCu₂I₃. Below this temperature, the light yield starts to decrease, which can be linked to the unusually large increase in the band gap energy of CsCu₂I₃.