Observation by ESR of electrons localized at intrinsic shallow traps in silver halide systems

Eachus, R. S.; Olm, M. T.; Janes, Robert R.; Symons, Martyn C. R.

doi:10.1002/pssb.2221520220

Cited by 21 publications

(12 citation statements)

References 13 publications

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“…It was suggested that the intrinsic binding core consists of an interstitial silver ion [5], but other models include a substitutional silver ion at a surface kink or an internal jog [2]. The intrinsic shallow electron centers have also been observed by EPR spectroscopy and they give an isotrupic, structureless line at g -1.88 in AgC1 [6] and g -1.49 in AgBr [7]. Until now, both optical and EPR spectroscopy have been unable to establish the structure of the binding core.…”

Section: Structure Of the Intrinsic Shallow Electron Center In Agcl Smentioning

confidence: 97%

“…The ENDOR transitions of silver nuclei are shown in Fig. 1(a) where the nuclear Zeeman frequencies of ' Ag (I = 1/2, 52%) and '" Ag (I = 1/2, 48%) are observable as dips at 6.224 and 7.156 MHz, respectively. Figure 1(b) shows the chlorine ENDOR transitions and the dips at 12.537 and 15.057 MHz indicate the nuclear Zeeman frequencies of 35C1 (I = 3/2, 76%) and 37Cl (I = 3/2, 24%), respectively.…”

Section: Structure Of the Intrinsic Shallow Electron Center In Agcl Smentioning

confidence: 99%

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Structure of the Intrinsic Shallow Electron Center in AgCl Studied by Pulsed Electron Nuclear Double Resonance Spectroscopy at 95 GHz

et al. 1995

Phys. Rev. Lett.

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In this Letter we report the first direct determination of the wave function of the intrinsic shallow electron center in silver chloride. A model is suggested in which an electron is shallowly trapped by two adjacent silver ions on a single cationic site. The information has been obtained by pulsed electron nuclear double resonance at 95 GHz and illustrates the potential of high-frequency EPR techniques for the study of defects in semiconductors.Intrinsic defect centers in inorganic crystals have attracted considerable attention, because of their importance for material science. In particular, the F center in alkali halides has occupied a central place. The identification of its structure was eventually solved by electron nuclear double resonance (ENDOR) spectroscopy.The results proved that this center consists of an electron trapped in the Coulombic field of a (substitutional) anion vacancy and that the alternative model, which assumed the presence of an electron bound to an interstitial cation, had to be rejected [1].The identification of the structure of the intrinsic shallow electron center in silver halides resembles the problem concerning the F center. Shallow electron centers are created upon uv excitation and are believed to play an important role in the latent image formation process [2,3]. They can be studied at low temperatures and were first observed in 1969 by Brandt and Brown using uv-induced infrared absorption spectroscopy [4]. It was suggested that the intrinsic binding core consists of an interstitial silver ion [5], but other models include a substitutional silver ion at a surface kink or an internal jog [2]. The intrinsic shallow electron centers have also been observed by EPR spectroscopy and they give an isotrupic, structureless line at g -1.88 in AgC1 [6] and g -1.49 in AgBr [7]. Until now, both optical and EPR spectroscopy have been unable to establish the structure of the binding core. In this Letter we report the first ENDOR spectra of intrinsic shallow electron centers in AgCl. They allow us to determine the spatial delocalization of the loosely bound electron and to propose a model for the binding core. The conclusions are supported by similar ENDOR results on the self-trapped exciton (STE) and on electrons shallowly bound to divalent cationic impurities. The ENDOR spectra were obtained via a method which is based on the stimulated echo (SE) pulse sequence [8]. Here a vr/2 r vr/2 T vr/2 micro-w-ave p-ul-se sequence is applied resonant with the EPR signal of the shallow electron center at g = 1.878. The SE signal is produced at time r after the third 7r/2 pulse. A radio frequency (RF) pulse between the second and third vr/2 pulse induces the nuclear transitions and its effect is monitored as a decrease of the SE intensity. The ENDOR spectra were recorded at 1.2 K with a spectrometer operating at a microwave frequency of 95 GHz. The spectrometer and its specific advantages for this work will be described in detail elsewhere [9]. The main experiment has been performed on an undoped AgC...

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Section: Structure Of the Intrinsic Shallow Electron Center In Agcl Smentioning

confidence: 97%

Section: Structure Of the Intrinsic Shallow Electron Center In Agcl Smentioning

confidence: 99%

Structure of the Intrinsic Shallow Electron Center in AgCl Studied by Pulsed Electron Nuclear Double Resonance Spectroscopy at 95 GHz

et al. 1995

Phys. Rev. Lett.

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“…The further enlargement of silver clusters can be understood to occur through transport of the mobile photoelectrons and interstitial silver ions and accumulation at one or at most a few growing centers. ESR experiments have also shown evidence for electron trapping in effective mass states that were extended lattice dislocations that penetrated the surface. Microwave photoconductivity experiments showed rapid electron trapping at sites thought to be surface kinks on a time scale of 10 ns at room temperature.…”

Section: Introductionmentioning

confidence: 99%

Properties of Silver Clusters Adsorbed to Silver Bromide

Baetzold

2001

J. Phys. Chem. B

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Density functional calculations of the structure and electronic properties of silver clusters interacting with a fragment of silver bromide that is embedded within a polarizable representation of the AgBr crystal are presented. Flat (001) surfaces and kinked surfaces are considered. The optimized geometry of the silver clusters is nearly planar for the clusters up to four atoms that are considered. We examined the degree to which different surface defect sites could modulate the properties of the adsorbed silver cluster. The positive kink site is unique in providing a location where the neutral cluster can capture photoelectrons. This effect can be rationalized by electrostatic arguments and is consistent with this site functioning as a location for photolytic silver formation. Other kink sites of neutral or partial negative charge do not permit electron trapping at neutral silver clusters. These sites could act as locations for chemically produced silver clusters. Calculations are presented showing that some geometries of Ag3 + adsorbed at the negative kink can trap electrons in accord with a proposal by Tani. The calculations are used to compare different mechanisms for photolytic formation of silver clusters. They can be compared to gas-phase calculations adjusted for the interaction with a polarizable surface to show that both calculations agree that cationic silver clusters are unstable with respect to dissociation except on the negative kink. The calculations show a deep electron trap depth for the silver atom consistent with its participation in the nucleation phase of silver cluster growth during photolysis. A sulfide ion substituted for bromide at a positive kink is shown to provide a means of coupling the electron to the crystal ions.

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“…18 Thus, the reduction and enhancement of the PC signal in the annealed and deformed crystal, respectively, can be explained in terms of the increased or decreased number of interstitial silver ions.…”

Section: Discussionmentioning

confidence: 99%

Photoinduced anomalous heat generation in AgCl and AgBr single crystals at liquid-helium temperature

1997

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Anomalous heat generation induced by band-gap light illumination was observed in AgCl and AgBr single crystals by a sensitive photocalorimetric method at liquid-helium temperature. The generated heat per second was estimated to be one to two orders of magnitude larger than the absorbed energy per second. This heat generation lasted for more than 10 h after termination of the band-gap light illumination, indicating that exothermic chain reactions were triggered by the absorbed photons. In a crystal which was not annealed, total emitted heat energy was estimated to be as high as 0.17 eV per unit cell. Consecutive nonradiative recombination of interstitial silver ions and vacancies mediated by the photoelectrons are tentatively proposed to be the responsible chain reactions. Although most of the features of the heat generation can be explained by the proposed mechanism, this mechanism requires an unrealistically high concentration of interstitial-vacancy pairs to explain the total emitted energy, leaving the observed anomalous phenomenon unexplained.

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Observation by ESR of electrons localized at intrinsic shallow traps in silver halide systems

Cited by 21 publications

References 13 publications

Structure of the Intrinsic Shallow Electron Center in AgCl Studied by Pulsed Electron Nuclear Double Resonance Spectroscopy at 95 GHz

Structure of the Intrinsic Shallow Electron Center in AgCl Studied by Pulsed Electron Nuclear Double Resonance Spectroscopy at 95 GHz

Properties of Silver Clusters Adsorbed to Silver Bromide

Photoinduced anomalous heat generation in AgCl and AgBr single crystals at liquid-helium temperature

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