Picosecond Studies of Transient Absorption Induced by BandGap Excitation of CsI and CsI:Tl at Room Temperature

Williams, Richard; Üçer, K. B.; Grim, Joel Q.; Lipke, Kyle C.; Trefilova, L.; Moses, W.W.

doi:10.1109/tns.2009.2033184

Cited by 28 publications

(17 citation statements)

References 13 publications

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“…Since the time for electron thermalization by LO phonons in iodide crystals has been calculated [4,5,7,14] to be on the order of a few picoseconds, the above line of reasoning indicates that the main nonlinear quenching is complete within a few picoseconds. This conclusion is consistent with previous time-resolved data directly [25] and indirectly [17] related to nonlinear quenching in CsI. The bottom line for the decision is that free carriers dominate the nonlinear quenching process in the right branch of Fig.…”

Section: Discussionsupporting

confidence: 93%

“…The rapid drop in free carrier absorption could be due to shallow capture of electrons in high Rydberg states around holes, transferring oscillator strength dominantly to the deep infrared spectrum out of our experimental spectral range, and to self trapping of holes which could transfer hole oscillator strength to the ultraviolet. The re-growth of absorption having a spectrum previously attributed to self-trapped excitons in CsI at room temperature [17] could represent relaxation of self-trapped excitons to their metastable radiative state. The time for that process is seen in Fig.…”

Section: η Eh (T E T); Born Excitons; Thermalization and Capture Of mentioning

confidence: 86%

“…[15] However for the time being, we assume that the trapping and bimolecular exciton formation channels turn on after a hot electron thermalization time approximated as 6 ps in iodide crystals. This estimate of 6 ps is chosen as representative of the 7 ps maximum thermalization time in CsI [4] and the 6 ps capture time of electrons on Tl + in CsI:Tl(0.3%) [17]. The free-carrier Auger recombination is similarly modeled as turning off when the carriers thermalize and trap on spatially separated sites (in CsI:Tl and similar activated scintillators, especially halides).…”

Section: Hot Free-carrier Kinetics and Associated Light Yield Modelmentioning

confidence: 99%

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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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Section: Discussionsupporting

confidence: 93%

Section: η Eh (T E T); Born Excitons; Thermalization and Capture Of mentioning

confidence: 86%

Section: Hot Free-carrier Kinetics and Associated Light Yield Modelmentioning

confidence: 99%

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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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“…The visible luminescence bands in CsI:Tl þ , which consist of two bands peaking at 2.55 and 2.25 eV, are attributed to the self-trapped exciton (STE) perturbed by a Tl þ ion [35][36][37] and/or the radiative recombination of an electron in a Tl 0 center with a neighboring V K center. 38,39) Reflecting the origin, the visible luminescence bands in CsI:Tl þ are efficiently induced by excitation at the Tl þrelated absorption bands located in the energy region higher than the A absorption band. In contrast, the visible luminescence bands in the Au À centers in cesium halides are efficiently excited at the energy position of the A and/or C absorption bands.…”

Section: Origin Of Visible Luminescence Bands In Au à Centers In Cesimentioning

confidence: 99%

Optical Properties of Au^-Centers in CsBr and CsI Single Crystals

Kawai

2012

J. Phys. Soc. Jpn.

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The temperature dependence of the absorption and luminescence spectra has been investigated for Au À centers in CsBr and CsI single crystals with the CsCl structure. In addition to the A, B, C, and D absorption bands, the A 0 and B 0 luminescence bands caused by the intraionic transitions in the Au À ion are observed at 12 K. The luminescence bands are characterized by a small Stokes shift and a narrow halfwidth, reflecting a weak electron-phonon interaction. Furthermore, the photoexcitation at the energies corresponding to the A, B, and C absorption bands induces luminescence bands in the visible energy region. The A 0 , B 0 , and visible luminescence bands change with temperature while complementing each other. The features of the Au À centers in cesium halides and the nonradiative transitions between the relaxed excited states are discussed.

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“…It is simply a competition in whether excitations will more quickly reduce their concentration n by the quenching itself (a loss of light emission) or by diffusion to larger radius (preserving possibility of light emission later at lower concentration). The time for nonlinear quenching, t NLQ , in which this competition effectively occurs has been measured in the range of 6–10 ps in CsI:Tl and NaI:Tl 1, 4. Recent work has pointed out that carriers may not be fully thermalized within this time scale of nonlinear quenching, and thus hot electron transport should be considered as well 5–8.…”

Section: Introductionmentioning

confidence: 99%

The roles of thermalized and hot carrier diffusion in determining light yield and proportionality of scintillators

Grim

Üçer

et al. 2012

Physica Status Solidi (a)

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Numerical modeling and comparison to experiment in the materials for which suitable parameters have been measured confirm that three of the most important material parameters for predicting proportionality and the related host‐dependent light yield (LY) of scintillators are (i) the carrier diffusion coefficients (including hole self‐trapping if present, and hot‐electron diffusion if unthermalized), (ii) the kinetic order and associated rate constant of nonlinear quenching, and (iii) deep‐trapping probability. Thermalized carrier diffusion appears sufficient to describe the main trends in oxides and semiconductors. For heavier halide hosts, it appears necessary to take account of hot‐electron diffusion to explain several important host‐dependent trends.

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Picosecond Studies of Transient Absorption Induced by BandGap Excitation of CsI and CsI:Tl at Room Temperature

Cited by 28 publications

References 13 publications

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

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

Optical Properties of Au^-Centers in CsBr and CsI Single Crystals

The roles of thermalized and hot carrier diffusion in determining light yield and proportionality of scintillators

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Picosecond Studies of Transient Absorption Induced by BandGap Excitation of CsI and CsI:Tl at Room Temperature

Cited by 28 publications

References 13 publications

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

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

Optical Properties of Au-Centers in CsBr and CsI Single Crystals

The roles of thermalized and hot carrier diffusion in determining light yield and proportionality of scintillators

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Optical Properties of Au^-Centers in CsBr and CsI Single Crystals