Ultralow-concentration Sm codoping in CsI:Tl scintillator: A case of little things can make a big difference

•The effects of ultralow-concentration Sm codoping on the scintillation characteristics of CsI:Tl were investigated.•Afterglow was dramatically lowered while maintaining the light yield and energy resolution values.•Application in CT medical imaging is discussed. CsI:Tl scintillators were hindered from computer tomography and high-speed imaging applications by a serious afterglow problem. In this study, the effects of ultralow-concentration Sm codoping on the scintillation characteristics of CsI:Tl were investigated. Pulsed X-ray excited afterglow after 50ms in 0.005mol% Sm-codoped CsI:Tl was lowered by over one order of magnitude in comparison with Sm-free one. The beneficial effects of ultralow-concentration Sm codoping also appeared to be maintaining the light yield and energy resolution. The light yield and energy resolution after 0.005mol% Sm codoping were 71,700±6000photons/MeV and 6.9% at 662keV, respectively.