The application of advanced theory and modeling techniques has become an essential component to understand material properties and hasten the design and discovery of new ones. This is true for diverse applications. Therefore, current efforts aimed towards finding new scintillator materials are also aligned with this general predictive approach. The need for large scale deployment of efficient radiation detectors requires discovery and development of high-performance, yet low-cost, scintillators. While Tl-doped NaI and CsI are still some of the widely used scintillators, there are promising new developments, for example, Eu-doped SrI2 and Ce-doped LaBr3. The newer candidates have excellent light yield and good energy resolution, but challenges persist in the growth of large single crystals. We will discuss a theoretical basis for anticipating improved proportionality as well as light yield in solid solutions of certain systems, particularly alkali iodides, based on considerations of hot-electron group velocity and thermalization. Solid solutions based on NaI and similar alkali halides are attractive to consider in more detail because the end point compositions are inexpensive and easy to grow. If some of this quality can be preserved while reaping improved light yield and possibly improved proportionality of the mixture, the goal of better performance at the low price of NaI:Tl might be attainable by such a route. Within this context, we will discuss a density functional theory (DFT) based study of two prototype systems: mixed anion NaIxBr1-x and mixed cation NaxK1-xI. Results obtained from these two prototype candidates will lead to further targeted theoretical and experimental search and discovery of new scintillator hosts.
There are thousands of halides that are potentially useful as scintillator hosts. Establishing understanding of trends and
fundamental mechanisms for energy transport is important for identifying those that are most likely to be useful. We
report calculations of electronic structures in relation to energy transport and optical properties in halide scintillators.
These include hybrid functional studies of rare earth activator energy levels, calculations of self-trapping energies of
carriers, and electronic structures in relation to energy transport in elpasolites. We use the relationship between
electronic structure and energy transport to suggest a path for identifying new high light output elpasolite scintillators.
We also present the electronic structure for TlPbI3, which with activation is a potential low band gap scintillator.
In this paper, we report theoretical studies of native defects and dopants in a number of room-temperature semiconductor
radiation detection materials, i.e., CdTe, TlBr, and Tl6SeI4. We address several important questions, such as what causes
high resistivity in these materials, what explains good μτ product (carrier mobility-lifetime product) in soft-lattice ionic
compounds that have high defect density, and how to obtain high resistivity and low carrier trapping simultaneously. Our
main results are: (1) shallow donors rather than deep ones are responsible for high resistivity in high-quality detectorgrade
CdTe; (2) large dielectric screening and the lack of deep levels from low-energy native defects may contribute to
the good μτ products for both electrons and holes in TlBr; (3) the polarization phenomenon in Tl6SeI4 is expected to be
much reduced compared to that in TlBr.
Conference Committee Involvement (4)
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XX
20 August 2018 | San Diego, California, United States
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIX
7 August 2017 | San Diego, California, United States
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XVIII
29 August 2016 | San Diego, California, United States
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XVII
10 August 2015 | San Diego, California, United States
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