Tailoring the Properties of Europium-Doped Potassium Calcium Iodide Scintillators Through Defect Engineering

Codoping is an effective approach for precise control of point defects in many advanced materials, and can be used to optimize their function. This paper reports an effort toward tailoring the scintillation properties of metal halides through defect engineering. A study of aliovalent codoping of the KCaI₃:Eu²⁺ single-crystalline scintillators is performed, through which it is discovered that a simultaneous suppression of X-ray induced afterglow and improvement of gamma-ray energy resolution can be successfully achieved via Zr⁴⁺ codoping. The afterglow level is reduced by more than twofold with Zr⁴⁺ codoping. The energy resolution of a 5 mm cubic KCaI₃:Eu²⁺ sample is improved from 3.25 to 2.7% at 662 keV, and 6.5 to 5.73% at 122 keV upon Zr⁴⁺ codoping. Physical explanations for the improvements are revealed from our investigations into both the electronic structure and thermodynamics of the defects by using thermoluminescence techniques and density functional theory calculations. The codoped Zr⁴⁺ ions prefer to form interstitials acting as shallow electron traps. The {Zr_Ca+V_Ca} complex can co-exist with Zr_i interstitials as shallow hole traps under certain condition, which are able to trap holes temporarily.