A first-principles investigation of excitation and emission processes of CsI(Tl) under near-UV radiation

Based on the analyses of excitation paths in CsI(Tl) under near-UV light ( lambda min = 220 nm), all possible excited states are modeled. The emission paths are revealed by the first-principles calculations performed for each excited state. Based on the analyses of band structure, density of states (DOS), and transition dipole moment (TDM), the theoretical range of central emission wavelength is proposed as 517 similar to 538 nm for the Tl-center luminescence and 375 similar to 405 nm for the intrinsic luminescence. This prediction agrees well with the experimental emission spectra, which have a peak at 514.2 nm and a shoulder at 410.6 nm. This method can be applied to CsI(Tl) under higher-energy radiation and other halide scintillator materials.