Photoluminescence characterization of scintillators for phoswich detectors

The challenge for advanced PET instrumentation is performance optimization in terms of spatial resolution and sensitivity. The phoswich approach, which leads to a better approximation of the interaction point, provides Depth-Of-Interaction information that can significantly reduce parallax error and improve image resolution. In some cases, the scintillator phoswich layers can have not only different decay times but also different characteristics such as light yields, emission spectra, densities, effective atomic numbers, and indices of refraction. Depending on these properties, light interactions between crystals are possible, which may either limit or enhance phoswich functionality. In this paper, we report experiments on the luminescence characteristics of some promising scintillator materials for PET which could be used in a phoswich detector, such as LaBr₃:Ce, LaCl₃:Ce, LSO:Ce, GSO:Ce, LPS:Ce, LuYAP:Ce, with an emphasis on investigating excitation/emission spectra, rise times and decay times. For each combination of front and back layer crystals, radioluminescence and photoluminescence spectra were obtained. A Bollinger-Thomas set-up was used to measure luminescence rise and luminescence decay characteristics. Light interactions between scintillator crystals in phoswich detectors were studied and the possibility of measuring convolved light as a result of absorption and re-emission by another crystal layer was experimentally evaluated.