Resonant Energy Transfer in Si Nanocrystal Solids

Limpens, Rens; Lesage, Arnon; Stallinga, Peter; Poddubny, Alexander N.; Fujii, Minoru; Gregorkiewicz, T.

doi:10.1021/acs.jpcc.5b06339

Cited by 29 publications

(29 citation statements)

References 31 publications

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“…2); this suggests that the observed excitation and concentration QY dependences are caused by the same effect. One might argue that, for semiconductor QDs, the process of emission and absorption is more complex than that for R6G, and therefore, the validity of the Kasha-Vavilov rule [31] might be weaker or not hold at all; this has led to various discussions of interesting novel physical phenomena in the recent literature [9][10][11][12][13][14][15][16][17][18]. The striking similarity in the behavior of R6G and the two types of QD materials indicates that the origin of the underestimation is the same, suggesting that a critical assessment and caution are required when interpreting such data, especially for samples absorbing below approximately 10%-15%.…”

Section: Resultsmentioning

confidence: 99%

“…where N and N * denote the integrated intensities (numbers of photons) at the excitation and emission wavelengths, respectively; I (λ) is the detected spectrum; and C is the correction factor for the spectral response of the detection system. The IS methodology is considered to be the most robust and reliable [1,8] and has been employed to study a wide variety of materials and for the discovery of novel photophysical effects [9][10][11][12][13][14][15][16][17][18]. The IS method is also utilized by the lighting industry, where commercial devices based on the IS method for QY measurements can be purchased from several spectroscopic companies [19,20].…”

Section: Introductionmentioning

confidence: 99%

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Quantum Yield Bias in Materials With Lower Absorptance

et al. 2019

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Photoluminescence (PL) quantum yield (QY), which is defined as the ratio of emitted to absorbed photons, is the central quantity that characterizes light-emitting materials. It is an important parameter to assess the light efficiency of new materials, as well as identify novel photophysical mechanisms. While QY measurements are performed as standard in research and industry, accurate measurements are challenging.Here, we show that, besides known inaccuracies, PL QY measurements exhibit a surprising systematic bias. QY values are underestimated by a factor of two or more for samples with lower absorption, which can even lead to misinterpretation of results. We combine PL QY measurements of diluted Rhodamine 6G and two different semiconductor quantum dot solutions, via the standard integrating sphere method, with analytical modeling and ray-tracing simulations and find that, independent of the setup and luminescence mechanism, all measurements suffer from the same systematic underestimation of the QY. Through statistical analysis of the measured emitted and absorbed photon numbers, we uncover the origin of this underestimation in the asymmetry of the ratio distribution for low absorption, together with setup-specific features, such as signal offsets and nonlinearities. We suggest a robust calibration procedure to correct for this bias for precise evaluation of the QY in materials used for bioimaging, biosensing, and optoelectronic or photovoltaic devices.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quantum Yield Bias in Materials With Lower Absorptance

et al. 2019

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“…[15,16] For the commercial use of siliconn anomaterialst ob erealized, acompleteunderstanding of their behavior and properties as well as the ability to control them reliably are essential. [17][18][19] Thus, am anifold of different studies have been performed on silicon nanomaterials, including studies on size-dependent emission, [19][20][21] low-temperature effects, [22][23][24][25][26] particle interactions, [27][28][29][30] and the influence of functionalization or oxidation. [24,[31][32][33][34] We present herein al ow-temperature study of functionalized silicon nanocrystals( SiNCs) that extends the so-far measured size range up to 9nmS iNCs.…”

Section: Introductionmentioning

confidence: 99%

Ensemble Effects in the Temperature‐Dependent Photoluminescence of Silicon Nanocrystals

Jakob

Javadi

Veinot

et al. 2019

Chemistry A European J

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In this work the temperature-dependent photoluminescence of alkyl-capped silicon nanocrystals with mean diameters of between 3a nd 9nmh as been investigated. The nanocrystals were characterizede xtensively by FTIR, TEM, powder XRD, and X-ray photoelectron spectroscopy prior to low-temperature and time-resolved photoluminescence spectroscopy experiments. The photoluminescence (PL) properties were evaluated in the temperature range of 41-300 K. We found that the well-known temperature-de-pendentb lueshift of the PL maximum decreases with increasingn anocrystal diameter and eventually becomes a redshift for nanocrystal diameters larger than 6nm. This implies that the observed shiftsc annotb ee xplained solely by band-gap widening, as is commonlya ssumed. We propose that the luminescence of drop-cast silicon nanocrystals is affectedby particlee nsemble effects,w hich can explain the otherwise surprising temperature dependence of the luminescencepeak.[a] M.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.

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“…Consequently, improvement of the PL QY has become a topic of intense research. These include, among other, an energy transfer and exciton diffusion between Si NCs of different characteristics ("bright" and "dark" NCs [5][6][7] ), multiple exciton generation by hot carriers, [8] sharing of excitation energy between proximal NCs, [9][10][11] and Indeed, the PL energy, absorption cross-section, as well as radiative and nonradiative recombination rates vary strongly with the NC diameter [2] and the optimal Si NC size.…”

Section: Introductionmentioning

confidence: 99%

“…[4] In general, the optical properties of solid-state dispersions of Si NCs are determined by those of individual NCs and by cooperative processes. These include, among other, an energy transfer and exciton diffusion between Si NCs of different characteristics ("bright" and "dark" NCs [5][6][7] ), multiple exciton generation by hot carriers, [8] sharing of excitation energy between proximal NCs, [9][10][11] and…”

Section: Introductionmentioning

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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Resonant Energy Transfer in Si Nanocrystal Solids

Cited by 29 publications

References 31 publications

Quantum Yield Bias in Materials With Lower Absorptance

Quantum Yield Bias in Materials With Lower Absorptance

Ensemble Effects in the Temperature‐Dependent Photoluminescence of Silicon Nanocrystals

Photoluminescence Quantum Yield in Ensembles of Si Nanocrystals

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