Self-trapped hole in silver chloride crystals: A pulsed EPR/ENDOR study at 95 GHz

Bennebroek, M.; Duijn-Arnold, A. van; Schmidt, Jan; Poluektov, Oleg G.; Баранов, П. Г.

doi:10.1103/physrevb.66.054305

Cited by 10 publications

(18 citation statements)

References 16 publications

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“…8,9 Recent low-temperature ENDOR studies on the isolated self-trapped hole ͑STH͒ in AgCl have suggested that it is localized over a central silver 4d x 2 −y 2 orbital and four surrounding chloride orbitals, forming a ͓AgCl 4 ͔ 2− unit. 10 Within the bulk, it is thought that the electron can become trapped at an interstitial silver ion at low temperatures, 11 which has been verified by more recent experiments, with the trap having been found to be very shallow. 12,13 Consequently, under normal operating conditions the mobility of the electrons will be unaffected by these centers, allowing them to reach surface traps rapidly.…”

Section: Introductionmentioning

confidence: 88%

Defect structures in the silver halides

et al. 2008

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We report a state of the art density functional theory study of the intrinsic defects within the rocksaltstructured silver halides. These materials are well known to favor Frenkel defect pairs over Schottky pairs-a key factor in their use as photographic materials. We report the defect structures and formation energies of the elementary point defects obtained using the supercell approximation. In agreement with recent experimental results, we find that the interstitial cation adopts a split-interstitial configuration, centered on a lattice site. The effects of electron or hole trapping on the defect centers in AgCl and AgBr are reported, including the formation energetics, structures, and spin localizations. Although limitations in the supercell method are evident, we have nevertheless obtained valuable new insights into the properties of these fascinating materials.

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Section: Introductionmentioning

confidence: 88%

Defect structures in the silver halides

et al. 2008

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“…In Fig. 7 a, the low-temperature ESE-detected EPR spectrum of the STH in AgCl crystal at 94.9 GHz recorded with the magnetic field oriented along the cubic axis 〈100〉 and under continuous UV irradiation is shown [ 27 ]. The EPR signals of the STH are indicated in the figure.…”

Section: Self-trapped Holesmentioning

confidence: 99%

Self-Trapped Excitons in Ionic-Covalent Silver Halide Crystals and Nanostructures: High-Frequency EPR, ESE, ENDOR and ODMR Studies

et al. 2010

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Silver halides have unique features in solid state physics because their properties are considered to be of borderline nature between ionic and covalent bonding. In AgCl, the self-trapped hole (STH) is centered and partly trapped in the cationic sublattice, forming an Ag2+ ion inside of a (AgCl6)4− complex as a result of the Jahn–Teller distortion. The STH in AgCl can capture an electron from the conduction band forming the self-trapped exciton (STE). Recent results of a study of STE by means of high-frequency electron paramagnetic resonance, electron spin echo, electron–nuclear double resonance (ENDOR) and optically detected magnetic resonance (ODMR) are reviewed. The properties of the STE in AgCl crystals, such as exchange coupling, the ordering of the triplet and singlet sublevels, the dynamical properties of the singlet and triplet states, and the hyperfine interaction with the Ag and Cl (Br) nuclei are discussed. Direct information about the spatial distribution of the wave function of STE unpaired electrons was obtained by ENDOR. From a comparison with the results of an ENDOR study of the shallow electron center and STH, it is concluded that the electron is mainly contained in a hydrogen-like 1s orbital with a Bohr radius of 15.1 ± 0.6 Å, but near its center the electron density reflects the charge distribution of the hole. The hole of the STE is virtually identical to an isolated STH center. For AgCl nanocrystals embedded into the KCl crystalline matrix, the anisotropy of the g-factor of STE and STH was found to be substantially reduced compared with that of bulk AgCl crystals, which can be explained by a considerable suppression of the Jahn–Teller effect in nanoparticles. A study of ODMR in AgBr nanocrystals in KBr revealed spatial confinement effects and allowed estimating the nanocrystal size from the shape of the ODMR spectra.

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“…2b) had non-zero magnetic moment of 0.013 , which is again in excellent agreement with experimental values of a d-orbital contribution to the spin density per nucleus of 0.014 . 19,35 This fact thus stresses the existence of unpaired electron charge lying beyond the domain associated with the AgCl6 4-complex. A detailed analysis of the present calculations leads to a total electronic charge of  8% lying outside the complex region.…”

Section: Stability Of Self-trapped Holes In Agclmentioning

confidence: 99%

“…In the particular case of AgCl, it has been experimentally shown that approximately 63% of the STH is localized in the p orbitals of the 6 Cl -ions surrounding the Ag 2+ ion 35 . On the other hand, numerous theoretical works have demonstrated the 5s(Ag) nature of the conduction band of AgCl and AgBr.…”

Section: Methodsmentioning

confidence: 99%

“…A detailed analysis of the present calculations leads to a total electronic charge of  8% lying outside the complex region. This figure can be compared with the value (15%) estimated from the analysis of ENDOR data 19,35 . Along this line the present results on AgCl also point out that the fraction of electronic charge on silver would be smaller than for AgCl6 4-formed in KCl:Ag 2+ .…”

Section: Stability Of Self-trapped Holes In Agclmentioning

confidence: 99%

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Stability and Polaronic Motion of Self-Trapped Holes in Silver Halides: Insight through DFT+UCalculations

et al. 2016

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Polarons and their associated transport properties are a field of great current interest both in chemistry and physics. In order to further our understanding of these quasi-particles, we have carried out first-principles calculations of self-trapped holes (STH) in the model compounds AgCl and AgBr, where extensive experimental information exists. Our calculations confirm that the STH solely stabilizes in AgCl but with a binding energy of only 165 meV, an order of magnitude smaller than that found for the Vk center in KCl. Key contributions to this stabilization energy come from the local relaxation along breathing (a1g) and Jahn-Teller (eg) modes in the AgCl6 4-unit. In order to study the transfer of the STH among silver sites we (i) use first-principles calculations to obtain the hopping barrier of the STH to first and second neighbors, involving eight distinct paths, using firstprinciples and (ii) construct a simple model, based on Slater-Koster parameters, that highlights the similarity of polaron transfer with magnetic superexchange. This allows one understanding why the movement of STH to second neighbors is highly enhanced with respect to closer ones. In agreement with experimental data and the model, the present calculations prove the existence of a dominant mechanism of polaronic motion that corresponds to the displacement of the STH to the next nearest sites in the <100> direction and a small barrier of 37 meV. This mechanism is dominated by the covalency inside a AgX6 4-complex (X:Cl;Br) thus explaining why the STH is not stabilized in AgBr following the increase of covalency due to the ClBr substitution. The present calculations confirm that ~10% of the charge associated with the STH in AgCl is lying outside the AgCl6 4-complex. This fact is behind the differences between optical and magnetic properties of the STH in AgCl and those observed in KCl:Ag 2+ .2

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Self-trapped hole in silver chloride crystals: A pulsed EPR/ENDOR study at 95 GHz

Cited by 10 publications

References 16 publications

Defect structures in the silver halides

Defect structures in the silver halides

Self-Trapped Excitons in Ionic-Covalent Silver Halide Crystals and Nanostructures: High-Frequency EPR, ESE, ENDOR and ODMR Studies

Stability and Polaronic Motion of Self-Trapped Holes in Silver Halides: Insight through DFT+UCalculations

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