Defect Engineering by Codoping in KCaI3:Eu2+ Single-Crystalline Scintillators

Abstract

Eu2+ doped alkali or alkali earth iodide scintillators with energy resolutions ≤3% at 662 keV promise the excellent discrimination ability for radioactive isotopes required for homeland security and nuclear non-proliferation applications. To extend their applications to X-ray imaging, such as computed tomography scans, the intense afterglow which delays the response time of such materials is an obstacle that needs to be overcome. However, a clear understanding of the origin of the afterglow and feasible solutions is still lacking. In this work, we present a combined experimental and theoretical combined investigation of the physical insights of codoping-based defect engineering which can reduce the afterglow effectively in

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

“…The absolute light yield of KCaI 3 :Eu 2+ ,Zr 4+ samples was estimated by using the single photoelectron method, and the data were plotted in Figure (a). The 0.03 and 0.5 mol.% Zr 4+ ‐codoped samples have almost the same light yield as the non‐codoped sample, about 72 000 ± 4000 photons/MeV, which differs from the decreased light yield observed in KCaI 3 :Eu 2+ codoped with trivalent ions (La, Gd, Y, and Sc) . The measured PL and scintillation decay curves could be fit well by single exponential function and double exponential functions, respectively.…”

“…TL analysis and DFT calculations indicate that the room temperature afterglow of KCaI 3 :Eu 2+ originates from iodine vacancies acting as deep electron traps with a depth of ≈1.0 eV below the conduction band minimum. The corresponding TL peaks are located between 300 and 450 K .…”

“…To achieve afterglow suppression in iodide scintillators can allow rapid data acquisition with significantly reduced persistence from previous sensed images, and improve the image quality. We recently proposed a defect engineering strategy by introducing cation interstitials to suppress the formation of iodine vacancy defects associated with the room temperature afterglow . In the current study, we first examine the effects of Zr 4+ codoping on the scintillation properties of KCaI 3 :Eu 2+ , including gamma‐ray energy resolution, X‐ray induced afterglow, absolute light yield, scintillation decay and non‐proportionality, and then clarify the relationship between defect structure and material properties by using thermoluminescence (TL) and density functional theory (DFT) calculations.…”

Role of Multiple Charge States of Ce in the Scintillation of ABO3 Perovskites

“…A number of past studies have focused on 5d-4f transitions for a range of lanthanide activators using bandstructure calculations [32][33][34][35][36][37]. A general consensus appears to be that for conventional local and semi-local exchange correlation functionals within DFT, such as the local-density approximation (LDA) or the generalized gradient approximation (GGA), the self-interaction error associated with the localized nature of the 4f electrons prohibits the calculation of accurate energy differences as well as the location of the energy bands.…”

“…A general consensus appears to be that for conventional local and semi-local exchange correlation functionals within DFT, such as the local-density approximation (LDA) or the generalized gradient approximation (GGA), the self-interaction error associated with the localized nature of the 4f electrons prohibits the calculation of accurate energy differences as well as the location of the energy bands. There have been attempts to overcome this problem either by using methods that go beyond DFT [30,33] or by performing electronic-structure calculations with the LDA+U or GGA+U approach [38,39] to get a better description of the localized 4f states of Ce compared to LDA or GGA [32,34,37]. However, it is needless to emphasize that care should be taken while approximating the exact 4f -5d excitation energies by the one-electron energies within the DFT framework.…”