Scintillation: mechanisms and new crystals

The physical mechanisms active in inorganic scintillators used for medical imaging are reviewed briefly. These include relaxation of electronic excitation following initial absorption of high-energy radiation, thermalization of electrons and holes, formation of excitons , charge carrier trapping on defects and self-trapping, transfer of excitation to luminescence centers, and emission of detectable light. Materials include intrinsic and activated insulating crystals and semiconductors involving several different luminescent centers and radiative processes. Fundamental limitations of scintillator performance and nonradiative processes arising from native defects and impurities that can limit scintillation light output are discussed. The properties of several recently reported scintillating crystals are also presented.