Surface State Analysis of Photobrightening in CdSe Nanocrystal Thin Films

Asami, Harumi; Abe, Yasuyuki; Ohtsu, Takeshi; Kamiya, Itaru; Hara, Michikazu

doi:10.1021/jp035484a

Cited by 86 publications

(99 citation statements)

References 9 publications

(18 reference statements)

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“…Furthermore, the photooxidation that is the mechanism for photodarkening is avoided because the experiment occurs under high vacuum (10 À5 mTorr). [36][37][38] This stability 39 is also demonstrated in Figure 2, and typical stabilities were observed over three days of separate experiments.…”

Section: B Fluorophore Selectionsupporting

confidence: 61%

CdSe/ZnS quantum dot fluorescence spectra shape-based thermometry via neural network reconstruction

Munro

Liu

Glorieux

et al. 2016

Journal of Applied Physics

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Articles you may be interested in Fluorescence resonance energy transfer measured by spatial photon migration in CdSe-ZnS quantum dots colloidal systems as a function of concentration Appl. Phys. Lett. 105, 203108 (2014) As a system of interest gets small, due to the influence of the sensor mass and heat leaks through the sensor contacts, thermal characterization by means of contact temperature measurements becomes cumbersome. Non-contact temperature measurement offers a suitable alternative, provided a reliable relationship between the temperature and the detected signal is available. In this work, exploiting the temperature dependence of their fluorescence spectrum, the use of quantum dots as thermomarkers on the surface of a fiber of interest is demonstrated. The performance is assessed of a series of neural networks that use different spectral shape characteristics as inputs (peak-based-peak intensity, peak wavelength; shape-based-integrated intensity, their ratio, full-width half maximum, peak normalized intensity at certain wavelengths, and summation of intensity over several spectral bands) and that yield at their output the fiber temperature in the optically probed area on a spider silk fiber. Starting from neural networks trained on fluorescence spectra acquired in steady state temperature conditions, numerical simulations are performed to assess the quality of the reconstruction of dynamical temperature changes that are photothermally induced by illuminating the fiber with periodically intensitymodulated light. Comparison of the five neural networks investigated to multiple types of curve fits showed that using neural networks trained on a combination of the spectral characteristics improves the accuracy over use of a single independent input, with the greatest accuracy observed for inputs that included both intensity-based measurements (peak intensity) and shape-based measurements (normalized intensity at multiple wavelengths), with an ultimate accuracy of 0.29 K via numerical simulation based on experimental observations. The implications are that quantum dots can be used as a more stable and accurate fluorescence thermometer for solid materials and that use of neural networks for temperature reconstruction improves the accuracy of the measurement. Published by AIP Publishing.

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Section: B Fluorophore Selectionsupporting

confidence: 61%

CdSe/ZnS quantum dot fluorescence spectra shape-based thermometry via neural network reconstruction

Munro

Liu

Glorieux

et al. 2016

Journal of Applied Physics

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“…1,2 One of the most intriguing phenomena observed with NCs is the enhancement of their photoluminescence ͑PL͒ over time during continuous illumination. [3][4][5][6][7][8][9][10][11][12][13][14] This effect was reported so far mostly for CdSe and CdSe/ ZnS NCs and has induced extensive discussion in literature. Recently it was observed also for PbS NCs embedded in thin polymer films 14 and for PbS NCs in glasses.…”

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confidence: 99%

“…Recently it was observed also for PbS NCs embedded in thin polymer films 14 and for PbS NCs in glasses. 7 Different mechanisms were proposed to explain the PL enhancement but its nature still remains controversial due to the strong dependence of the NCs emissive properties on their surface quality, [3][4][5] as well as on the excitation intensity, 5-8 film morphology, 4,8,9 substrate-NCs interactions, 4,10 and environmental conditions. [11][12][13][14][15] The PL enhancement ͑PLE͒ has not been reported previously for PbSe NCs.…”

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confidence: 99%

“…In fact, our results show the opposite-the PL increase is highest in vacuum. The PL enhancement in vacuum can be understood in terms of two of the proposed mechanisms for PL increase in NCs films-photoinduced surface transformation 3,5,12,14 and photoelectrification. 4,20,21 In the first case, upon illumination of the NCs, optimization of surface-ligand passivation occurs, which neutralizes the existing surface defects.…”

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confidence: 99%

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Photoluminescence enhancement in thin films of PbSe nanocrystals

Christova

Stouwdam

Eijkemans

et al. 2008

Applied Physics Letters

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Remarkable photoluminescence enhancement (PLE) in submonolayer films of PbSe nanocrystals (NCs) upon continuous illumination was observed. The intensity increase from films on InP substrates was highest in vacuum, while for films on Si/SiO2 substrates the PLE was stronger in air. The magnitude of the PLE was found to depend on the excitation intensity, being higher for a weaker irradiation power. The possible mechanisms behind the phenomenon of the PLE are discussed and it is suggested to originate mainly from charge trapping outside the NCs core.

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“…Previous studies reported that the oxidation of the CdSe surface could cause a PL shift and QE decrease, which could be accelerated during the exposure to UV. [28][29][30] Core/shell NCs exhibited enhanced photostability compared to the core NCs, but the QE of core/shell NCs continuously decreased under UV exposure in a certain period of time. When the ZnS shell is thick, QE decreases faster because the thick shell causes large strain between the core and shell, caused by lattice mismatch.…”

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confidence: 99%