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Triplet-Triplet Exciton Annihiliation for Pulse Shape Discrimination in Scintillator Detectors (collaboration with J. Siegrist, LBNL)

Triplet-Triplet Exciton Annihiliation for Pulse Shape Discrimination in Scintillator Detectors (collaboration with J. Siegrist, LBNL)

The underlying mechanism enabling pulse shape discrimination of differing particle types in scintillating materials is the production of delayed fluorescence photons.  The intensity ratio of delayed to prompt florescence can be correlated to the energy density deposited by the detected particle with higher energy density resulting in larger delayed florescence intensity.  The observation of prompt and delayed florescence is the result of an allowed transition of the first excited singlet (S=0) quantum state to the ground singlet quantum state or the scintillating molecule.  In addition to the excited singlet states, a number of triplet states (S=1) are populated from the initial energy deposition.  These transition of triplet to singlet ground states is a first forbidden transition and thus occur at a much slower rate making these triplet states metastable to the order of milliseconds.  Within the lifetime of the triplet states, it is possible for the excited state to transfer from one spatial location to another by means of exciton transport mechanisms.  During this period, triplet states may transfer to singlet states by inter-system transfer or may annihilate with other triplet states producing a ground singlet and excited singlet states.  The resulting excited singlet states will de-excite to the ground state producing a delayed fluorescence photon.  Inter-system transfer should not vary with the energy density but triplet-triplet annihilation (TTA) should show higher rates given higher initial energy deposition.  Particle discrimination using pulse shape techniques rely on the understanding of the transport and annihilation of triplet excitons. The goal of this project is to investigate the triplet exciton transport properties under varying amounts of hydrostatic pressure and temperature with the aim of developing a general model for exciton transport. (collaboration with J. Siegrist, LBNL)
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