| 1. |
- Fares, Hssen, et al.
(författare)
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Tuning multicolor emission in AgNCs/Tm3+/Mn2+-doped fluorophosphate glasses
- 2020
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093. ; 535
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Tidskriftsartikel (refereegranskat)abstract
- Herein we report the synthesis of highly-doped silver nanocluster in fluorophosphate glasses through the melting-quenching method in order to achieve sensitization with Tm3+ and Mn2+ ions. Blue and red emission belonging to Tm3+ (470 to 490 nm) and Mn2+ (550 to 750 nm) ions could be obtained via non-resonant excitation of Tm3+ and Mn2+. Slight decrease of the fluorescence decay times confirmed an energy transfer as a possible mechanism to explain the Tm3+ and Mn2+ emission. The composition of 5 mol% of AgNO3, 0.4 mol% of Tm2O3 and 0.2 mol% of MnF2 in our sample leads to distance between donor (silver nanoclusters) and acceptor (Tm3+-Mn2+) as short as 11 Å, which suggests that the main mechanism for blue and red emission from Tm3+ and Mn2+ is Förster Resonance Energy Transfer (FRET). The results presented here show that the studied material has potential application for multicolor generation as luminophore in white light emitting diodes (W-LED).
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| 2. |
- Fucikova, Anna, et al.
(författare)
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The shell matters : one step synthesis of core-shell silicon nanoparticles with room temperature ultranarrow emission linewidth
- 2020
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 222:0, s. 135-148
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Tidskriftsartikel (refereegranskat)abstract
- Here we present a one-step synthesis that provides silicon nanocrystals with a thin shell composed of a ceramic-like carbonyl based compound, embedded in a porous organosilicon film. The silicon nanocrystals were synthesised from hydrogen silsesquioxane molecules, modified with organic molecules containing carbonyl groups, which were annealed at 1000 degrees C in a slightly reducing 5% H-2 : 95% Ar atmosphere. The organic character of the shell was preserved after annealing due to trapping of organic molecules inside the HSQ-derived oxide matrix that forms during the annealing. The individual silicon nanocrystals, studied by single dot spectroscopy, exhibited a significantly narrower emission peak at room temperature (lowest linewidth similar to 17 meV) compared to silicon nanocrystals embedded in a silicon oxide shell (150 meV). Their emission linewidths are even significantly narrower than those of single CdSe quantum dots (>50 meV). It is hypothesized that the Si-core-thin shell structure of the nanoparticle is responsible for the unique optical properties. Its formation within one synthesis step opens new opportunities for silicon-based quantum dots. The luminescence from the produced nanocrystals covers a broad spectral range from 530-720 nm (1.7-2.3 eV) suggesting strong application potential for solar cells and LEDs, following the development of a suitable mass-fabrication protocol.
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| 3. |
- Pevere, Federico, et al.
(författare)
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Biexciton Emission as a Probe of Auger Recombination in Individual Silicon Nanocrystals
- 2015
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:13, s. 7499-7505
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Tidskriftsartikel (refereegranskat)abstract
- Biexciton emission from individual silicon nanocrystals was detected at room temperature by time-resolved, single-particle luminescence measurements. The efficiency of this process, however, was found to be very low, about 10-20 times less than the single exciton emission efficiency. It decreases even further at low temperature, explaining the lack of biexciton emission line observations in silicon nanocrystal single-dot spectroscopy under high excitation. The poor efficiency of the biexciton emission is attributed to the dominant nonradiative Auger process. Corresponding measured biexciton decay times then represent Auger lifetimes, and the values obtained here, from tens to hundreds of nanoseconds, reveal strong dot-to-dot variations, while the range compares well with recent calculations taking into account the resonant nature of the Auger process in semiconductor nanocrystals.
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| 4. |
- Straskova, Adela, et al.
(författare)
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Proteome analysis of an attenuated Francisella tularensis dsbA mutant : identification of potential DsbA substrate proteins
- 2009
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Ingår i: Journal of Proteome Research. - : American Chemical Society (ACS). - 1535-3893 .- 1535-3907. ; 8:11, s. 5336-5346
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Tidskriftsartikel (refereegranskat)abstract
- Francisella tularensis (F. tularensis) is highly infectious for humans via aerosol route and untreated infections with the highly virulent subsp. tularensis can be fatal. Our knowledge regarding key virulence determinants has increased recently but is still somewhat limited. Surface proteins are potential virulence factors and therapeutic targets, and in this study, we decided to target three genes encoding putative membrane lipoproteins in F. tularensis LVS. One of the genes encoded a protein with high homology to the protein family of disulfide oxidoreductases DsbA. The two other genes encoded proteins with homology to the VacJ, a virulence determinant of Shigella flexneri. The gene encoding the DsbA homologue was verified to be required for survival and replication in macrophages and importantly also for in vivo virulence in the mouse infection model for tularemia. Using a combination of classical and shotgun proteome analyses, we were able to identify several proteins that accumulated in fractions enriched for membrane-associated proteins in the dsbA mutant. These proteins are substrate candidates for the DsbA disulfide oxidoreductase as well as being responsible for the virulence attenuation of the dsbA mutant.
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| 5. |
- Sychugov, Ilya, et al.
(författare)
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Ultranarrow Luminescence Linewidth of Silicon Nanocrystals and Influence of Matrix
- 2014
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 1:10, s. 998-1005
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Tidskriftsartikel (refereegranskat)abstract
- The luminescence linewidth of individual silicon nanocrystals was characterized by single-dot spectroscopy, and an ultranarrow linewidth of similar to 200 mu eV at 10 K was found. This value is, in fact, limited by system resolution and represents only the upper limit of the homogeneous linewidth. In addition, the effect of the matrix was investigated for nanocrystals coated with organic ligands, embedded in silicon dioxide, as well as for nanocrystals with only a thin passivating layer. It was found that, depending on the matrix, the room-temperature bandwidth may vary by an order of magnitude, where values as small as similar to 12 meV (similar to 5 nm) at 300 K were detected for nanocrystals with a thin passivation. The observed values for silicon nanocrystals are similar and even surpass some of those for direct-band-gap quantum dots. The narrow linewidth at room temperature enables the use of silicon nanocrystals for nontoxic narrow-band labeling of biomolecules and for application as phosphors in white-light-emitting devices.
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| 6. |
- Valenta, Jan, et al.
(författare)
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Light-Emission Performance of Silicon Nanocrystals Deduced from Single Quantum Dot Spectroscopy
- 2008
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 18:18, s. 2666-2672
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Tidskriftsartikel (refereegranskat)abstract
- Spectra of individual silicon nanocrystals within porous Si grains are studied by the wide-field imaging microspectroscopy and their ON-OFF, blinking is detected by the confocal single-photon-counting microscopy. Observed spectral and blinking properties comprise all features reported before in differently prepared single Si nanocrystals (SiNCs). Former apparently contradictory results are shown to be due to different experimental conditions. When the effect of dark periods (OFF switching) is removed the common ultimate photoluminescence properties Of SiO2 passivated SiNCs are found, namely the quantum efficiency (QE) of about 10-20% up to the pumping rate corresponding to one exciton average excitation per quantum dot. At higher pump rates the QE is slowly decreasing as the 0.7th power of excitation. This is most likely due to Auger recombination which, however, seems to be weakened compared with measurements of nanocrystal assemblies. We conclude that SiNCs may be pumped above one exciton occupancy to yield a higher light emission, being advantageous for applications.
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