Suppression of afterglow in CsI:Tl by codoping with Eu2+—II: Theoretical model

Bartram, R.H.; Kappers, L.A.; Hamilton, Douglas S.; Łempicki, A.; Brecher, C.; Głodo, J.; Gaysinskiy, V.; Ovechkina, E.E.

doi:10.1016/j.nima.2005.11.051

Cited by 42 publications

(23 citation statements)

References 18 publications

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“…As indicated earlier, our recent work [5,6] has identified Eu 2+ as the first codopant ion capable of achieving major reduction of the afterglow in CsI:Tl crystal scintillators. In short pulse excitation, its influence is felt as early as 10 µs after the end of the pulse, and lasts as long as 50 ms later.…”

Section: Afterglow Suppressionmentioning

confidence: 58%

“…These calculations require experimental input from two related types of measurement: afterglow, which describes the rate of escape of carriers from lattice traps, at ambient temperature; and thermoluminescence, which uses the temperature dependence of such escape to probe the depth and abundance of those traps. Such a modeling effort was particularly successful in the case of the CsI:Tl,Eu material system [5,6], and while the details of the mathematical computations are too lengthy to present here, we can briefly summarize the relevant points:…”

Section: Mechanism Of the Phenomenonmentioning

confidence: 99%

“…We have found [5] that by codoping the CsI:Tl with appropriately chosen dipositive rare earth ions, the afterglow can be lowered by almost two orders of magnitude. This unusual effect is attributed to the introduction of deep electron traps at the codopant sites, which divert electrons that had thermally escaped from shallow traps associated with thallium, thereby suppressing the delayed radiative recombination responsible for afterglow [6,7]. But the details of the suppressant effect are very much dependent on the identity of the codopant ion.…”

Section: Introductionmentioning

confidence: 99%

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Scintillation properties and applications of reduced-afterglow co-doped CsI:Tl

et al. 2007

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While a wide variety of new scintillators are now available, CsI:Tl remains a highly desired material for medical and industrial applications due to its excellent properties, low cost, and easy availability. Despite its advantages, however, its use in high-speed imaging applications has been hindered by an undesirably high afterglow component in its scintillation decay. To address this specific issue and to make the material suitable for applications such as volumetric CT and high-speed radiography, we have discovered that codoping the material with certain dipositive rare earth ions is particularly effective for such afterglow suppression. We have extensively studied the manner in which one such ion, Eu 2+ , alters the spectroscopic and kinetic properties of the scintillation, and have developed a coherent mathematical model consistent with the experimental results.Unfortunately, the beneficial effect of Eu 2+ appears to be restricted only to relatively short times (say < _ 200 ms) after the end of the excitation pulse. At longer times, the carriers whose diversion into deep traps is responsible for suppression of the short-term afterglow begin to escape those traps, resulting in enhancement of the low-level persistence on a time scale of seconds or minutes. What is needed is to provide some nonradiative means to annihilate the trapped carriers before their escape can enhance the low-level long-term emission. And, as predicted by the mathematical model, this is exactly what Sm 2+ does.In this paper we compare the respective effects of the two additives on the afterglow and hysteresis characteristics of the host CsI:Tl material system. We find that while Eu begins to exert its afterglow-suppressive effect sooner after termination of excitation, the influence of Sm lasts much longer. Moreover, the suppressive effect of the latter is always found, regardless of the conditions of excitation, and becomes more profound the greater the duration of the exciting pulse. Various aspects of these effects and some their consequences for imaging performance are also discussed.

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Section: Afterglow Suppressionmentioning

confidence: 58%

Section: Mechanism Of the Phenomenonmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Scintillation properties and applications of reduced-afterglow co-doped CsI:Tl

et al. 2007

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“…We discovered that the addition of a second dopant, Eu 2+ , was capable of substantially reducing the afterglow exhibited by CsI:Tl crystal scintillators. Our observations [7] and theoretical analysis [8] indicated that Eu 2+ ions introduce deep electron traps at the codopant sites, which divert electrons that had thermally escaped from shallow traps associated with thallium, thereby suppressing the delayed radiative recombination responsible for afterglow. This immediately made the material useful for applications such as high-speed radiography, from which it had earlier been excluded.…”

Section: Introductionmentioning

confidence: 98%

Suppression of Afterglow in Microcolumnar CsI:Tl by Codoping With Sm$^{2+}$: Recent Advances

Nagarkar

Thacker

Gaysinskiy

et al. 2009

IEEE Trans. Nucl. Sci.

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Microcolumnar CsI:Tl remains a highly desirable sensor for digital X-ray imaging due to its superior spatial resolution, bright emission, high absorption efficiency, and ready availability. Despite such obvious advantages, two characteristic properties of CsI:Tl undermine their use in clinical and high speed imaging: a persistent afterglow in its scintillation decay, and a hysteresis effect that distorts the scintillation yield after exposure to high radiation doses.In our earlier work we have discovered that the addition of 0.05 to 0.5 mol percent of Sm 2+ to crystals of CsI:Tl suppresses their afterglow by a factor of up to 50, even when subjected to a very high exposure of 120 R. This additive also diminishes hysteresis by an order of magnitude, which is a major accomplishment. Consequent-ly, our work is now focused on developing codoped microcolumnar CsI:Tl, Sm films that can potentially combine excellent properties of the current state-of-the-art CsI:Tl films with the reduced afterglow and hysteresis observed in codoped crystals. While our earlier attempts in CsI:Tl, Sm film fabrication, reported at the previous IEEE meeting, demonstrated obvious advantages of the approach, the recent work has succeeded in producing films that show improvement by at least a factor of 7 in afterglow and 150% in brightness compared to the standard CsI:Tl films. We report these important results in this paper, along with other recent advances in film growth and new imaging results.

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“…We have found that by codoping the CsI:Tl with Eu 2+ , the afterglow in the time range of 10 μs-100 ms can be lowered by almost two orders of magnitude. We have conducted an extensive investigation of this unusual effect [5], and have derived a detailed mathematical model that explains the underlying kinetic processes [6]. It is the purpose of this paper to discuss some of these results, outline recent developments in terms of fabricating CsI:Tl,Eu microcolumnar films for X-ray imaging applications, and to present their imaging characteristics.…”

Section: Introductionmentioning

confidence: 99%

Low-afterglow CsI:Tl microcolumnar films for small animal high-speed microCT

Thacker

Singh

Gaysinskiy

et al. 2009

Nuclear Instruments and Methods in Physics Research Section A:

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Dedicated high-speed microCT systems are being developed for noninvasive screening of small animals. Such systems require scintillators with high spatial resolution, high light yield, and minimal persistence to ensure ghost free imaging. Unfortunately, the afterglow associated with conventional CsI:Tl microcolumnar films used in current high-speed systems introduces image lag, leading to substantial artifacts in reconstructed images, especially when the detector is operated at several hundreds of frames per second. At RMD, we have discovered that the addition of a second dopant, Eu 2+ , to CsI:Tl crystals suppresses the afterglow by as much as a factor of 40 at 2 ms after a short excitation pulse of 20 ns, and by as much as a factor of 15 at 2 ms after a long excitation pulse of 100 ms. Our observations, supported by theoretical modeling, indicate that Eu 2+ ions introduce deep electron traps that alter the decay kinetics of the material, making it suitable for many high-speed imaging applications. Here we report on the fabrication and characterization of CsI:Tl,Eu microcolumnar films to determine if the remarkable afterglow properties of CsI:Tl,Eu crystals are preserved in the CsI:Tl,Eu microcolumnar films. Preliminary results indicate that the codoped microcolumnar films show a factor of 3.5 improvement in the afterglow compared to the standard CsI:Tl films.

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Suppression of afterglow in CsI:Tl by codoping with Eu2+—II: Theoretical model

Cited by 42 publications

References 18 publications

Scintillation properties and applications of reduced-afterglow co-doped CsI:Tl

Scintillation properties and applications of reduced-afterglow co-doped CsI:Tl

Suppression of Afterglow in Microcolumnar CsI:Tl by Codoping With Sm$^{2+}$: Recent Advances

Low-afterglow CsI:Tl microcolumnar films for small animal high-speed microCT

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