Single-dot absorption spectroscopy and theory of silicon nanocrystals

Sychugov, Ilya; Pevere, Federico; Luo, Jun-Wei; Zunger, Alex; Linnros, Jan

doi:10.1103/physrevb.93.161413

Cited by 42 publications

(46 citation statements)

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“…Under blue/UV excitation the resulting 2 × 2 × 0.2 cm slabs exhibited diffused red and green luminescence arising from the embedded Si and CdSe QDs, respectively. Structures containing Si QDs offer a unique opportunity to evaluate scattering losses because the optically active Si QDs have negligible reabsorption at the emission wavelength . The scattering strength of the luminescence was found to be dependent on the wood fiber direction, consistent with the original wood structure being preserved.…”

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confidence: 58%

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Luminescent Transparent Wood

Veinot

et al. 2016

Advanced Optical Materials

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(1 of 5) 1600834 transition, where different nanocrystal materials were tested. Under blue/UV excitation the resulting 2 × 2 × 0.2 cm slabs exhibited diffused red and green luminescence arising from the embedded Si and CdSe QDs, respectively. Structures containing Si QDs offer a unique opportunity to evaluate scattering losses because the optically active Si QDs have negligible reabsorption at the emission wavelength. [15] The scattering strength of the luminescence was found to be dependent on the wood fiber direction, consistent with the original wood structure being preserved. High scattering values (i.e., up to ≈ 10 dB cm −1 ) indicate strong suppression of the total internal reflection required for emitted light propagation. This luminescent transparent wood nanocomposite offers interesting possibilities for applications, which can benefit from its unique structural and optical properties. Examples would be furniture for general lighting or luminescent solar concentrators for building integration, [16][17][18][19] where the proven mechanical strength of this transparent wood [11] is a clear advantage. The nontoxicity and material abundance of Si QDs further enables sustainable and large scale manufacturing of this new luminescent material.Silicon QDs were synthesized upon processing of hydrogen silsesquioxane by thermal annealing. [20] The resulting nanocrystal-containing silicon oxide composites were treated with ethanolic hydrofluoric acid to extract hydride terminated nanocrystals. It was followed by surface passivation using wellestablished hydrosilylation procedures described elsewhere. [21,22] Toluene dispersions of the resulting alkyl-passivated Si QDs feature external photoluminescence quantum yields in the range 30%-60%. [23] Samples used here had peak positions in the red (720 nm) and near infrared (870 nm) spectral range. To demons trate the possibility of incorporating different types of QDs commercially available CdSe/ZnS core/shell quantum dots with green emission (540 nm, Evident Technologies) were used.The wood template was obtained by delignification of wood veneer (balsa, Ochroma pyramidale, purchased from Wentzels Co. Ltd, Sweden) with dimension of 2 × 2 × 0.2 cm to remove the main light-absorbing component. [24] The thickness direction of the veneer is the tangential direction of the cross-section of the tree stem. Specifically, wood veneer was treated using 1 wt% of sodium chlorite (NaClO 2 , Sigma-Aldrich) in acetate buffer solution (pH 4.6) at 80 °C. The reaction was stopped when the wood appeared almost uniformly white. The delignified samples were washed with deionized water and kept in water until further use. Prior to polymer infiltration, wood samples were dehydrated upon sequential exposure to ethanol and acetone with each solvent exchange step repeated three times. The MMA monomer was pre-polymerized before mixing with QDs. The prepolymerization was completed by heating the MMA at 75 °C for 15 min with 0.3 wt% 2,2′-azobis (2-methylpropionitrile) followed by cooling to room temp...

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confidence: 58%

“…The use of Si QDs with an appreciable apparent Stokes shift ensures the measured extinction is mainly contributed by scattering. It is known that light‐emitting states of these Si QDs remain largely of indirect bandgap character leading to long (≈µs) luminescence lifetimes and strongly suppressed reabsorption at the emission wavelength …”

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confidence: 99%

Luminescent Transparent Wood

Veinot

et al. 2016

Advanced Optical Materials

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137

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“…[165] These findings led Luo and coworkers to the conclusion that early explanations on the "anticonfinement" effect were not supported by atomistic calculations. [166] Toward the utilization of electronic spins in Si for qubits and the circumvention of intrinsic limitations of this material for spin quantum computing, a numerically inverse designed Si quantum well for the isolation of a single electron valley state in Si by a "magic sequence" of Ge/Si barrier layers was reported. [167] In terms of optoelectronic applications of silicon, highperformance photodetectors had been recently developed through heavy-boron (B) doping in Si nanocrystals (Figure 7).…”

Section: Silicon Nanomaterialsmentioning

confidence: 99%

Advances in Functional Nanomaterials Science

Rahimi‐Iman

2020

Annalen der Physik

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Technologies employing nanomaterials, such as electronics, optoelectronics, nanobiotechnologies, quantum optics, and nanophotonics, are perceived as the key drivers of investigations on novel and functional materials and their nanostructures for various applications. It is well understood that the study of such materials and structures has been of great importance for the optimization and development of electrical and optical devices. From such devices, one does not only expect higher efficiencies, but also access to the development of completely new concepts, which are strongly demanded by modern information‐processing, quantum, or medical technologies, and sensing applications. In this context, a wide range of aspects such as the physics of novel materials, as well as materials engineering, characterization, and applications are summarized here. Novel materials, which can be used, for instance, for energy harvesting or light generation, as well as for future logic devices; material engineering, which can lead to improved device functionality and performance in optoelectronics; material physics, the study of which allows insight to be gained into optical and electrical properties of nanostructured systems and quantum materials; and technologies/devices, addressing progress on the application side of sophisticated material systems and quantum structures, are highlighted using representative examples.

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“…[42] In that way the enhanced PL QY in the energy range of the "special" points would evidence the onset of the SSQC, whose positive contribution to the overall PL QY could subsequently be suppressed by the negative effect of, e.g., increased carrier trapping simultaneously promoted by the high excitation energy. [43][44][45] In any case, the variation of the Γ 25 → Γ 15 transition energy with the NC size makes its correlation with the PL QY dependence dubious. In the present study, no general correlation of PL QY characteristics with any specific energy values has been found.…”

Section: Additional Remarksmentioning

confidence: 99%

“…3. the experiment suggests that the Γ 25 → Γ 15 transition should down-shift upon quantum confinement, [1] the theoretical modeling of this effect, and even the degree to which it can be identified for Si NCs, is a matter of debate between different theoretical approaches. [43][44][45] In any case, the variation of the Γ 25 → Γ 15 transition energy with the NC size makes its correlation with the PL QY dependence dubious. 4.…”

Section: Additional Remarksmentioning

confidence: 99%

Photoluminescence Quantum Yield in Ensembles of Si Nanocrystals

Chung

Limpens

Gregorkiewicz

2017

Advanced Optical Materials

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energy exchange with defects. [2,12] The strength of the cooperative processes and their effect on the optical properties of an NC ensemble depend on the characteristics of the individual NCs themselves as well as on the ensemble properties, such as NC density and proximity, [13] confining potential of the embedding matrix [14] and its quality, etc. [6] The cooperative processes typically involve an energy barrier for their activation, and therefore will change with the excitation energy. On the other hand, it is well known that the Kasha-Vavilov rule, [15] which states that the PL QY is independent of the excitation energy, is frequently violated for colloidal semiconductor NCs, [16] since carriers that are photogenerated higher in the conduction/ valence bands experience an increased probability of capturing at defect states and/or escape to the outside of an NC, leading to its ionization [10] and a temporal loss of optical activity. In result, the PL QY of the NCs decreases typically at short pump wavelengths. In this study, we investigate the excitation energy dependence of the PL QY for Si NC layers and find that it varies strongly in different samples. We investigate and discuss possible physical mechanisms influencing the PL QY at different excitation energies and conclude on an important role of impact excitation and parasitic absorption. Sample PreparationThe samples used in this study were produced by a co-sputtering method in the form of multilayer (ML) structures, featuring multiple stacks (up to 100) of 3.5 nm thin active layers of Si NCs separated by SiO 2 barriers. In this process, two sputtering guns, with Si and SiO 2 targets, are used. By operating both guns simultaneously, an Si-rich substoichiometric SiO x "active" layer can be grown, while solely the gun with silicon dioxide is applied to develop a barrier layer of pure SiO 2 . The atomic composition of the active layer can be tuned by adjusting the power of the guns, and the layer thickness is controlled by the exposure time. For the samples investigated in this study, the silicon excess of 15%, 25%, and 30% was used in the active layer. The barrier thickness between two adjacent active layers was set at 5 nm to avoid exciton diffusion between these layers. [17] Extensive past research [18,19] has shown that, in contrast to thick homogeneous layers of Si NCs in SiO 2 , ML structures allow for a better size control and therefore yield ensembles with a more narrow size distribution.This study investigates the photoluminescence quantum yield for cosputtered solid-state dispersions of Si nanocrystals in SiO 2 with different size and density, and concludes that the absolute value of the photoluminescence quantum yield shows a varied dependence on the excitation energy. Physical mechanisms influencing the photoluminescence quantum yield at different excitation energy ranges are considered. Based on the experimental evidence, this study proposes a generalized description of the excitation dependence of photoluminescence quantum yield of Si nanocrys...

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Single-dot absorption spectroscopy and theory of silicon nanocrystals

Abstract: Single-dot absorption spectroscopy and theory of silicon nanocrystals. Phys. Rev. B, 93http://dx

Cited by 42 publications

References 35 publications

Luminescent Transparent Wood

Luminescent Transparent Wood

Advances in Functional Nanomaterials Science

Photoluminescence Quantum Yield in Ensembles of Si Nanocrystals

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