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Single crystals of Eu2+-activated SrI2, one of the most leading-edge scintillators for gamma-ray spectroscopy applications, have a low radioactive background, excellent energy resolution of 2.6%–3% at 662 keV, and high light yield of 80 000–120 000 photons/MeV. In this article, tetravalent ions codoping, namely, Hf4+ codoping, was used to enhance its scintillation performance. $\emptyset 12$ mm diameter SrI2:Eu2+ single crystals codoped with 0, 0.05, 0.1, and 0.2 at% Hf4+ were successfully grown by the multiampoule Bridgman method. All grown crystals are highly transparent, crack-free, and inclusion-free. The effects of Hf4+ codoping concentration on the optical and scintillation properties were studied. The gamma-ray energy resolutions of SrI2:Eu single crystals can be improved from 3.4% to 3.1% at 662 keV, and from 6.6% to 6.0% at 122 keV upon 0.05 at% Hf4+ codoping. [ABSTRACT FROM AUTHOR]

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 {ZrCa+VCa} complex can co‐exist with Zri interstitials as shallow hole traps under certain condition, which are able to trap holes temporarily. [ABSTRACT FROM AUTHOR]