In recent years, the development of new semiconductor photodetectors, e.g., avalanche photodiodes (APD), silicon photomultipliers (SiPM), and TFT (thin-film transistor), lead to an increased interest in red and infrared emitting scintillators. These photodetectors allow the construction of more compact and robust scintillation detection units, are compatible with magnetic fields, and exhibit generally higher quantum efficiency than photomultipliers. Moreover, red/IR emitting scintillators of smaller band-gap are theoretically able to outperform more common UV/blue emitting scintillators in terms of light yield and energy resolution.
Czech Technical University has built a new APD-based amplitude spectrometry setup for red/IR emitting scintillator characterization. The performance of the setup was tested using high quality GGAG:Ce,Mg (Gd3Ga2Al3O12:Ce,Mg) crystal. Measurements of light yield, energy resolution, proportionality, timing characteristics were carried out. Independently, the light yield of the GGAG:Ce,Mg sample was determined by HPMT-based setup for verification purposes. Also, setup performance dependence on bias voltage was studied.
Two sets of samples with different dopant concentration were characterized by an amplitude spectrometry setup based on APD: Cs3Cu2I5:In and CsEuBr:Sm. Light yield and energy resolution were determined. The best sample Cs3Cu2I5:In(0.2 %) exhibited light yield 43 600 photons/MeV and 5.0 % FWHM under 137Cs irradiation. The response of a black scintillator Cs4EuBr6:Sm samples is much less promising: light yield 5740 ph/MeV at best and FWHM is above 20 %.
With light yield 43 600 ph/MeV and good optical quality of Cs3Cu2I5:In(0.2 %) single crystal, good performance in intended application, i.e. x-ray imaging, was expected. Indeed, Cs3Cu2I5-based imaging system exhibit resolution 16 lp/mm.