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

Abstract

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 KCaI 3 :Eu 2þ 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 Zr 4þ codoping. The afterglow level is reduced by more than twofold with Zr 4þ codoping. The energy resolution of a 5 mm cubic KCaI 3 :Eu 2þ sample is improved from 3.25 to 2.7% at 662 keV, and 6.5 to 5.73% at 122 keV upon Zr 4þ 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 Zr 4þ ions prefer to form interstitials acting as shallow electron traps. The {Zr Ca þV Ca } complex can co-exist with Zr i interstitials as shallow hole traps under certain condition, which are able to trap holes temporarily.Scintillators coupled with photodetectors are widely used for radiation detection applications such as homeland security, medical imaging, high energy physics, and oil well logging. Driven by the increasing requirements of practical applications, many high-performance inorganic scintillators, including oxides and metal halides, have been discovered and developed during recent decades. [1] For the homeland security applications, radioisotope identification is implemented by passive nuclear detection systems through high-resolution gamma spectroscopy measurements. To achieve high confidence and high specificity detection of nuclear threats with a low rate of false alarms the detector used must have excellent energy resolution. This is also important for the single photon emission computed tomography application as it helps to screen out the scattered gamma rays that carry false positioning information. Several recently developed halide scintillators can have energy resolutions of 3% at 662 keV, such as LaBr 3 :Ce 3þ , [2] SrI 2 : Eu 2þ , [3] CsBa 2 I 5 :Eu 2þ , [4] KSr 2 I 5 :Eu 2þ , [5] KCaI 3 :Eu 2þ , [6] and KCa 0.8 Sr 0.2 I 3 :Eu 2þ . [7] Codoping has become an increasingly popular strategy to engineer inorganic scintillators toward optimal function for targeted applications for the past 20 years. [1,8] Nonetheless, very few studies reported successful improvement of energy resolution of metal halides by codoping, only the binary halides have been improved by aliovalent codoping. [9][10][11] The energy resolution of LaBr 3 :Ce 3þ and CeBr 3 single crystals can be optimized to %2 and 3% at 662 keV, respectively, by Sr 2þ or Ca 2þ codoping. [9,10] This improvement has been ascribed to the reduction of the non-radiative Auger quenching effect by formation of energetically shallower electron traps....

Czochralski Growth, Optical, Scintillation, and Defect Properties of Cu2+ Codoped Lu2SiO5:Ce3+ Single Crystals

“…Tetravalent cation codoping, such as Zr 4+ , Hf 4+ , and Ge 4+ , can enhance the scintillation yield of Gd 2 SiO 5 :Ce due to the reduction in Ce 4+ concentration . Sr 2+ codoping can improve the gamma-ray spectral resolution of LaBr 3 :Ce 3+ to 2.0% at 662 keV, and Zr 4+ codoping can enhance the spectral resolution of SrI 2 :Eu 2+ and KCaI 3 :Eu 2+ to 2.5% and 2.7% at 662 keV, because of a more proportional light yield response. − Aluminate garnets, such as Lu 3 Al 5 O 12 :Ce (LuAG:Ce) and (Lu 0.75 Y 0.25 ) 3 Al 5 O 12 :Pr (LuYAG:Pr), can approach an excellent energy resolution of 4% at 662 keV by Mg 2+ and Li + codoping, respectively, owing to an improvement in counting statistics resulting from the enhancement of light yield. , The 5d-4f emission of stable Ce 4+ is as efficient as stable Ce 3+ under ionization irradiation, but with a faster lifetime due to the bypass of the first step of the stable Ce 3+ scintillation emission, namely capturing a hole from the valence band. Aliovalent codoping was proven to shorten the decay time of Ce doped oxides by introducing stable Ce 4+ , for example, a 36% shortening of the fast component for Gd 3 Ga 3 Al 2 O 12 :Ce (GGAG:Ce) and 7% for LuAG:Ce by Mg 2+ codoping. , For bulk single-crystal scintillators grown using the Czochralski method, a codopant may not only influence the performance, but also the crystallization behavior.…”

Advanced Halide Scintillators: From the Bulk to Nano

“…[166,167] Moreover, codoping with RE 3þ results in significant suppression of the afterglow, [168] while Zr 4þ codoping results in improvement of energy resolution. [169] Growth of large volume crystals (up to Ø50 mm) is possible without significant deterioration of the scintillation performance. [61] The Yb 2þ -doped ACaCl 3 (A ═ Cs, Rb, K) crystals show emission bands centered at %445 nm with two decay time constants of %10 and 200 μs in the PL and scintillation decays attributed to fast (LS) and slow (HS) 5d-4f transition of Yb 2þ , respectively.…”

An active and stable multifunctional catalyst with defective UiO-66 as a support for Pd over the continuous catalytic conversion of acetone and hydrogen

“…In common, the defects in UiO-66 can be tailored via adjusting the synthesis conditions, including incorporation of modulators, [27][28][29] thermal activation/dehydration, 30 metal cation substitution 31 and linker modication. 32 In this paper, the utilizing of the mixture Zr-precursor of ZrOCl 2 $8H 2 O and ZrCl 4 was rstly developed to create defect-rich UiO-66 and then Pd was loaded thereon to fabricate the multifunctional catalyst for acetone hydrogenation reaction. As expected, the catalytic performance results exhibited that a high active and stable catalyst was achieved, with the at least 1000 h stability with MIBK + MIBC selectivity of 84.87-93.07% and acetone conversion of 45.26-53.22%.…”

“…In common, the defects in UiO-66 can be tailored via adjusting the synthesis conditions, including incorporation of modulators, 27–29 thermal activation/dehydration, 30 metal cation substitution 31 and linker modification. 32 …”