Nonexponential relaxation dynamics of localized carrier densities in oxide crystals without structural or energetic disorder

Merschjann, Christoph; Imlau, Mirco; Brüning, H.; Schoke, B.; Torbrügge, Stefan

doi:10.1103/physrevb.84.052302

Cited by 14 publications

(16 citation statements)

References 24 publications

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“…11 However, a general analytical description of hopping transport is in most cases impossible, and one has to turn to numerical approaches, e.g., random-walk simulations. 22,29 These analyses depend crucially on the assumptions made and a thorough investigation is beyond the scope of this initial work. One commonly used model is that of an exponentially decreasing transfer rate with increasing distance between hopping sites, in our case the monomer units.…”

Section: Time Dependence and Transport Phenomenamentioning

confidence: 99%

“…27,28,33 (3) Possible transport of the excitation via resonant energy transfer or hopping of excitons results in a strongly nonexponential decay of the PL signal. 22,29,31 The transition rate for hopping transport is likely to be proportional to the (exponentially decreasing) overlap of the π orbitals of cofacial aromatic systems. 29 In consequence, the lifetime of the PL decay grows exponentially with larger interplanar stacking distances in the polymer.…”

Section: Process-temperature Dependence and A Qualitative Modelmentioning

confidence: 99%

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Photophysics of polymeric carbon nitride: An optical quasimonomer

et al. 2013

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A comprehensive investigation of the luminescent properties of carbon nitride polymers, based on tri-s-triazine units, has been conducted. Steady-state temperature-and excitation-power-dependent as well as time-resolved measurements with near-UV excitation (λ = 325 nm and 405 nm) yield strong photoluminescence, covering the visible spectrum. The spectral, thermal, and temporal features of the photoluminescence can be satisfactorily described by the excitation and radiative recombination of molecular excitons, localized at single tri-s-triazine units. The discussed model is in accordance with the recently reported absorption features of carbon nitride polymers. Thus, from the point of view of optical spectroscopy, the material effectively behaves as a monomer.

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Section: Time Dependence and Transport Phenomenamentioning

confidence: 99%

Section: Process-temperature Dependence and A Qualitative Modelmentioning

confidence: 99%

Photophysics of polymeric carbon nitride: An optical quasimonomer

et al. 2013

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“…The measured decay and disappearance of the polaron state, and the absence of any new spectral features such as a trap-state or chargetransfer state absorption, confirms that the excited carriers are recombining while self-trapped in the polaron. The measured long-timescale dynamics are best-fitted using the stretched exponential theory for polaron hopping between trap states 46,47 ,…”

mentioning

confidence: 99%

“…3a). The stretching factor β in the exponential represents the sum over all possible hopping paths to a terminal defect site 46,47 . When β is one, the stretched exponential reduces to an exponential decay and the excited carrier decays almost on-site with a defect-state-determined lifetime of τ .…”

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confidence: 99%

Excitation-wavelength-dependent small polaron trapping of photoexcited carriers in α-Fe2O3

et al. 2017

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Small polaron formation is known to limit ground-state mobilities in metal oxide photocatalysts. However, the role of small polaron formation in the photoexcited state and how this affects the photoconversion efficiency has yet to be determined. Here, transient femtosecond extreme-ultraviolet measurements suggest that small polaron localization is responsible for the ultrafast trapping of photoexcited carriers in haematite (α-FeO). Small polaron formation is evidenced by a sub-100 fs splitting of the Fe 3p core orbitals in the Fe M edge. The small polaron formation kinetics reproduces the triple-exponential relaxation frequently attributed to trap states. However, the measured spectral signature resembles only the spectral predictions of a small polaron and not the pre-edge features expected for mid-gap trap states. The small polaron formation probability, hopping radius and lifetime varies with excitation wavelength, decreasing with increasing energy in the t conduction band. The excitation-wavelength-dependent localization of carriers by small polaron formation is potentially a limiting factor in haematite's photoconversion efficiency.

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“…This is a purely phenomenological representation and is used to interpret experimental results in many fields of physical science ,. There are four adjustable parameters for each recovery curve; M (∞), M (0), R *, and β. R * is the “characteristic relaxation rate” and β is the “stretching parameter”.…”

Section: Discussionmentioning

confidence: 99%

Proton Spin‐Lattice Relaxation in Organic Molecular Solids: Polymorphism and the Dependence on Sample Preparation

et al. 2018

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We report solid-state nuclear magnetic resonance H spin-lattice relaxation, single-crystal X-ray diffraction, powder X-ray diffraction, field emission scanning electron microscopy, and differential scanning calorimetry in solid samples of 2-ethylanthracene (EA) and 2-ethylanthraquinone (EAQ) that have been physically purified in different ways from the same commercial starting compounds. The solid-state H spin-lattice relaxation is always non-exponential at high temperatures as expected when CH rotation is responsible for the relaxation. The H spin-lattice relaxation experiments are very sensitive to the "several-molecule" (clusters) structure of these van der Waals molecular solids. In the three differently prepared samples of EAQ, the relaxation also becomes very non-exponential at low temperatures. This is very unusual and the decay of the nuclear magnetization can be fitted with both a stretched exponential and a double exponential. This unusual result correlates with the powder X-ray diffractometry results and suggests that the anomalous relaxation is due to crystallites of two (or more) different polymorphs (concomitant polymorphism).

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Nonexponential relaxation dynamics of localized carrier densities in oxide crystals without structural or energetic disorder

Cited by 14 publications

References 24 publications

Photophysics of polymeric carbon nitride: An optical quasimonomer

Photophysics of polymeric carbon nitride: An optical quasimonomer

Excitation-wavelength-dependent small polaron trapping of photoexcited carriers in α-Fe2O3

Proton Spin‐Lattice Relaxation in Organic Molecular Solids: Polymorphism and the Dependence on Sample Preparation

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