CsI:Tl+,Yb2+: ultra-high light yield scintillator with reduced afterglow

Abstract

The afterglow problem has been preventing CsI:Tl single crystal scintillators from being used for applications in the field of computer tomography and high-speed imaging. We show that Yb²⁺ codoping in CsI:Tl can reduce it at least by one order of magnitude after 50 ms from X-ray cut-off compared to ordinary CsI:Tl. After optimization of the Yb²⁺ and Tl⁺ concentrations, the doubly doped CsI:Tl,Yb crystal exhibits an ultra-high light yield of 90 000 ± 6000 photons MeV⁻¹, energy resolution 7.9%@511 keV and low afterglow level of about 0.035% at 80 ms. Simultaneous improvement in afterglow, light yield and energy resolution in CsI:Tl-based scintillators paves the way to its application in computer tomography and high-speed imaging. The physical mechanism and role of ytterbium ions in afterglow suppression are proposed.