Bright infrared scintillators for gamma spectroscopy

Despite years of impressive progress in development of new scintillators for gamma spectroscopy, energy resolution offered is still lagging direct detection solid state devices. Even the best scintillators do not convert more than about 30% of the initial energy into photons, and this introduces the Poisson component in the photodetector, which can become a limiting factor. On top of that, the efficiency of scintillation is strongly dependent on excitation density, so not only the number of generated photons is smaller than the initial number of electron-hole pairs, but the conversion process is subjected to additional fluctuations due to ionization density fluctuation (nonproportionality on average and pulse-to-pulse fluctuations). This stochastic pulse-to-pulse variation contributes to resolution limitation. Further progress in improving energy resolution requires to address all these issues at the same time: starting from high electron-hole production efficiency, through energy conversion into light, and ending on matching scintillation emission with superior sensitivity and noise characteristic of a photodetector. One route points to small bandgap materials (such as “black scintillators”) which have potential for obtaining extremely high light yields and match well high quantum efficiency of silicon-based photodetectors. In recent works we showed that europium-doped scintillators can be converted into near infrared emitters by samarium co-doping and provide high energy resolution in gamma spectroscopy. Alternatively, novel metal halide perovskites may become the way to higher energy resolution goal, but there are some significant problems to be solved. The ideas developed with “black scintillators” may alleviate some of obstacles found in perovskites.