Kinetic Monte Carlo simulations of excitation density dependent scintillation in Cs<scp>I</scp> and Cs<scp>I</scp>(<scp>T</scp>l)

Wang, Zhiguo; Williams, Richard; Grim, Joel Q.; Gao, Fei; Kerisit, Sebastien N.

doi:10.1002/pssb.201248587

Cited by 33 publications

(19 citation statements)

References 48 publications

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“…The thermal velocities estimated from jump rate times average jump length for STH and STE in alkali iodides are about the same. 50,61 The parameter S 1E has little effect in fitting proportionality because the population of STEs free of thallium is very small in Tl-doped CsI, mainly due to the enormous trapping rate S 1e of electrons on thallium as measured in ps absorption experiments.…”

Section: Materials Parameters and Proportionalitymentioning

confidence: 99%

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

Bizarri

et al. 2015

Phys. Rev. B

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A high-energy electron in condensed matter deposits energy by creation of electron-hole pairs whose density generally increases as the electron slows, reaching the order of 10 20 eh/cm 3 near the end of its track. The subsequent interactions of the electrons and holes include nonlinear rate terms and transport as first hot and then thermalized carriers in the nanometer-scale radial dimension of the track. Charge separation and strong radial electric fields occur in a material such as CsI with contrasting diffusion rates of self-trapped holes and hot electrons. Eventual radiative recombination has a nonlinear relation to the primary electron energy because of these interactions. This socalled intrinsic nonproportionality of electron response limits achievable energy resolution of a given scintillation radiation detector material. We use a system of coupled transport and rate equations to describe a pure host (3 equations) and one dopant (4 more equations per dopant). Applying it first to the experimentally well-characterized system of CsI and CsI:Tl in this work, we use results of picosecond absorption spectroscopy, interband z-scan measurements of nonlinear rate constants, and other experiments and calculations to determine most of the more than 20 rate and transport coefficients required for modeling. The model is solved in a track environment approximated as cylindrical and is compared to the proportionality curve and total light yield of undoped CsI at temperatures of 295 K and 100 K, as well as thallium dopant in CsI:Tl at 295 K. With this degree of validation, the space-and time-distributions of carriers and excitons, both untrapped and trapped, are examined within the model to gain an understanding of the main competitions controlling the nonproportionality of response.

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Section: Materials Parameters and Proportionalitymentioning

confidence: 99%

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

Bizarri

et al. 2015

Phys. Rev. B

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“…Superimposed in Fig. 9 is the Kinetic Monte Carlo (KMC) simulation of 2 nd order quenching [18,19], fitted to the laser PDR data [9]. As mentioned in the Introduction, the PDR experiment is measured without the complex track structure and associated gradients driving diffusion that occur in gamma-ray or electron excited luminescence.…”

Section: Mixed Kinetic Order In Nai and Kinetic Monte Carlo Simulatiomentioning

confidence: 99%

“…SLYNCI) and K-dip. [18,19] with experimental PDR results (solid circles) [9] for NaI(0.1% Tl) excited by 5.9-eV photons as a function of the position of the beam waist (z-position) and excitation density. Figure 8 Photon density response of NaI:Tl excited at 6.1 eV and 5.9 eV.…”

Section: Mixed Kinetic Order In Nai and Kinetic Monte Carlo Simulatiomentioning

confidence: 99%

Experimental and computational results on exciton/free-carrier ratio, hot/thermalized carrier diffusion, and linear/nonlinear rate constants affecting scintillator proportionality

Williams

Grim

et al. 2013

SPIE Proceedings

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Models of nonproportional response in scintillators have highlighted the importance of parameters such as branching ratios, carrier thermalization times, diffusion, kinetic order of quenching, associated rate constants, and radius of the electron track. For example, the fraction η eh of excitations that are free carriers versus excitons was shown by Payne and coworkers to have strong correlation with the shape of electron energy response curves from Compton-coincidence studies. Rate constants for nonlinear quenching are implicit in almost all models of nonproportionality, and some assumption about track radius must invariably be made if one is to relate linear energy deposition dE/dx to volume-based excitation density n (eh/cm 3 ) in terms of which the rates are defined. Diffusion, affecting time-dependent track radius and thus density of excitations, has been implicated as an important factor in nonlinear light yield. Several groups have recently highlighted diffusion of hot electrons in addition to thermalized carriers and excitons in scintillators. However, experimental determination of many of these parameters in the insulating crystals used as scintillators has seemed difficult. Subpicosecond laser techniques including interband z scan light yield, fluence-dependent decay time, and transient optical absorption are now yielding experimental values for some of the missing rates and ratios needed for modeling scintillator response. First principles calculations and Monte Carlo simulations can fill in additional parameters still unavailable from experiment. As a result, quantitative modeling of scintillator electron energy response from independently determined material parameters is becoming possible on an increasingly firmer data base. This paper describes recent laser experiments, calculations, and numerical modeling of scintillator response.

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“…Existing models depend on external parameters, such as dielectric functions, stopping power, migration barriers, defect properties, polaron formation, and migration, as well as nonradiative recombination rates. [15][16][17][18][19][20][21] Another example is the Monte-Carlo model of gamma-ray response that requires accurate knowledge of the electron-energy loss function. 22 In principle, all these quantities can be deduced either from experiment or from first-principles modeling.…”

Section: Introductionmentioning

confidence: 99%

Excitons in scintillator materials: Optical properties and electron-energy loss spectra of NaI, LaBr₃, BaI₂, and SrI₂

Schleife

Zhang

et al. 2016

J. Mater. Res.

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Materials for scintillator radiation detectors need to fulfill a diverse set of requirements such as radiation hardness and highly specific response to incoming radiation, rendering them a target of current materials design efforts. Even though they are amenable to cutting-edge theoretical spectroscopy techniques, surprisingly many fundamental properties of scintillator materials are still unknown or not well explored. In this work, we use first-principles approaches to thoroughly study the optical properties of four scintillator materials: NaI, LaBr 3 , BaI 2 , and SrI 2 . By solving the Bethe-Salpeter equation for the optical polarization function we study the influence of excitonic effects on dielectric and electron-energy loss functions. This work sheds light into fundamental optical properties of these four scintillator materials and lays the ground-work for future work that is geared toward accurate modeling and computational materials design of advanced radiation detectors with unprecedented energy resolution.

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Kinetic Monte Carlo simulations of excitation density dependent scintillation in CsI and CsI(Tl)

Cited by 33 publications

References 48 publications

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

Experimental and computational results on exciton/free-carrier ratio, hot/thermalized carrier diffusion, and linear/nonlinear rate constants affecting scintillator proportionality

Excitons in scintillator materials: Optical properties and electron-energy loss spectra of NaI, LaBr₃, BaI₂, and SrI₂

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Kinetic Monte Carlo simulations of excitation density dependent scintillation in CsI and CsI(Tl)

Cited by 33 publications

References 48 publications

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

Experimental and computational results on exciton/free-carrier ratio, hot/thermalized carrier diffusion, and linear/nonlinear rate constants affecting scintillator proportionality

Excitons in scintillator materials: Optical properties and electron-energy loss spectra of NaI, LaBr3, BaI2, and SrI2

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Excitons in scintillator materials: Optical properties and electron-energy loss spectra of NaI, LaBr₃, BaI₂, and SrI₂