| 1. |
- Balmes, Olivier, et al.
(författare)
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Cryo-TEM observation of 3-dimensionally ordered aggregates of 5-nm gold particles in organic solvents
- 2004
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Ingår i: Journal of Nanoparticle Research. - : Springer Science and Business Media LLC. - 1572-896X .- 1388-0764. ; 6:6, s. 569-576
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we show evidence for the assembly of ordered 3-dimensional aggregates of 5-nm gold particles in toluene, 1-octanol, n-decane, and chloroform. The use of plunge-freezing allows to freeze the solution containing the aggregates at a rate which does not allow reorganisation of the particles during sample preparation. The samples were then observed using cryo-transmission electron microscopy (cryo-TEM) showing that most of the particles were part of ordered aggregates, thus proving that organisation already exists in solution. In some cases, the stability of the sample under the electron beam made it possible to record several pictures of the same aggregate at different angles and build animated tilt series.
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| 2. |
- Balmes, Olivier, et al.
(författare)
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Homogeneous surface-enhanced Raman scattering observed from self-assembled gold nanoparticle films deposited from the liquid-liquid interface
- 2005
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Ingår i: Vibrational Spectroscopy. - : Elsevier BV. - 0924-2031. ; 37:2, s. 189-193
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Tidskriftsartikel (refereegranskat)abstract
- The self-assembled gold nanoparticle film deposited from the liquid-liquid interface has been fabricated, and homogeneous surfaceenhanced Raman scattering (SERS) of R6G molecules on the film has been observed. The SERS enhancement factor of the film is estimated to be in the range 10(8)-10(10). Occasionally, there are some sudden jumps in the Raman signal, where the signal is increased a few times. Such jumps are probably caused by single-molecule SERS in some extremely "hot" sites. (c) 2004 Elsevier B.V. All rights reserved.
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| 3. |
- Balmes, Olivier, et al.
(författare)
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Imaging atomic structure in metal nanoparticles using high-resolution cryo-TEM
- 2006
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Ingår i: Microscopy and Microanalysis. - 1435-8115. ; 12:2, s. 145-150
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Tidskriftsartikel (refereegranskat)abstract
- It has been shown, by imaging gold (200) planes, that it is possible to achieve better than 0.20-nm structural resolution in cryo-transmission electron microscopy (cryo-TEM). This has been done using commercially available cryo equipment and using a 300-kV field emission gun (FEG) TEM. The images of 15-nm gold particles embedded in amorphous frozen water clearly show the (111) planes (separated by 0.235 nm) in gold. Fourier transform demonstrates the presence of (200) planes in the image, proving a resolution of better than 0.20 nm. The experimental results are Supported by image simulations using the multislice method. These simulations suggest that it should be possible to achieve the same resolution even in smaller particles and particles of lighter elements. The crucial experimental problem to overcome is keeping the thickness of the amorphous film low and to work at low electron dose conditions.
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| 4. |
- Balmes, Olivier, et al.
(författare)
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Self-healing and self-organized gold nanoparticle films at a water/organic solvent interface
- 2006
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 0000-0000. ; 6:1, s. 130-134
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Tidskriftsartikel (refereegranskat)abstract
- Gold nanoparticles (5 nm and 20 nm) have been synthesized and stabilized with mercaptoundecanol. These particles, although insoluble in water or common organic solvents, spread as a thin film at the liquid-liquid interface between a water phase and an organic phase. Films of these gold nanoparticles have been observed both by conventional transmission electron microscopy of deposited samples and by cryo-transmission electron microscopy of plunge-frozen samples. The film can be monolayered and extend over centimeter-sized areas. The particle films spontaneously re-assemble and self-organize at the interface when disrupted. This self-healing capacity of the film should make it possible to build a device for continuous production and deposition of the film.
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| 5. |
- Carlsson, A, et al.
(författare)
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The first structure determination of nanosized colloidal particles of Pd3P by high-resolution electron microscopy
- 1998
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Ingår i: Angewandte Chemie (International edition). - 1433-7851. ; 37:9
-
Tidskriftsartikel (refereegranskat)abstract
- The exact three-dimensional structure of a nanosized colloidal particle of Pd3P was determined directly from high-resolution transmission electron microscopy (HRTEM) images that were recorded in several crystallographic directions. An HRTEM image recorded along [011] is shown on the right. The cores of the particles were excluded from the analysis because of severe multiple diffraction.
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| 6. |
- Chen, Wei, et al.
(författare)
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Crystal field, phonon coupling and emission shift of Mn2+ in ZnS:Mn nanoparticles
- 2001
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89, s. 1120-1129
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Tidskriftsartikel (refereegranskat)abstract
- The Mn2+ emission wavelengths are at 591, 588, 581 and 570 nm, respectively, for the similar to 10, similar to4.5, similar to3.5 nm sized nanoparticles and the ZnS:Mn nanoparticles formed in an ultrastable zeolite-Y. To reveal the cause for the shift, the crystal field and phonon coupling were investigated. The results show that the predominant factor for the shift is the phonon coupling, whose strength is size dependent and is determined by both the size confinement and the surface modification of the nanoparticles. Although the crystal field strength decreases with the decreasing of the particle size, its change has little contribution to the emission shift of Mn2+ in ZnS:Mn nanoparticles. (C) 2001 American Institute of Physics.
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| 7. |
- Chen, Wei, et al.
(författare)
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Energy structure and fluorescence of Eu2+ in ZnS:Eu nanoparticles
- 2000
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Ingår i: Physical Review B. - 1098-0121. ; 61:16, s. 11021-11024
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Tidskriftsartikel (refereegranskat)abstract
- Eu2+-doped ZnS nanoparticles with an average size of around 3 nm were prepared, and an emission band around 530 nm was observed. By heating in air at 150 degrees C, this emission decreased, while the typical sharp line emission of Eu3+ increased. This suggests that the emission around 530 nm is from intraion transition of Eu2+: In bulk ZnS:Eu2+, no intraion transition of Eu2+ was observed because the excited states of Eu2+ are degenerate with the continuum of the ZnS conduction band. We show that the band gap in ZnS:Eu2+ nanoparticles opens up due to quantum confinement, such that the conduction band of ZnS is higher than the first excited state of Eu2+, thus enabling the intraion transition of Eu2+ to occur.
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| 8. |
- Chen, W, et al.
(författare)
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Full-Color Emission and Temperature Dependence of the Luminescence in Poly-P-phenylene ethynylene-ZnS/Mn2+ Composite Particles
- 2003
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 107:27, s. 6544-6551
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of a nanocomposite material composed of anionic poly(phenylene ethynylene) (aPPE) polymer particles and ZnS/Mn2+ nanoparticles is described, and its luminescence properties are investigated. aPPE particles have two emissions, one in the blue (460 nm) and the other in the green (490 nm), that are assigned to the 0-0 transition and an excimer, respectively. ZnS/Mn2+ nanoparticles have an emission at 596 nm that is due to the T-4(1)-(6)A(1) transition of Mn2+ and an emission at 706 nm that is ascribed to defect-related luminescence. The blue, green, yellow, and red emissions make the composite a potential material for full-color displays. More interestingly, the relative intensities of the different emissions may be varied by changing the excitation energy. Infrared spectra reveal that interactions exist between the two particles; however, photoluminescence excitation and emission spectra as well as observations of luminescence lifetimes indicate that there is negligible energy transfer from the polymer particles to the ZnS/Mn2+ nanoparticles. Temperature studies reveal that the ZnS/Mn2+ particles in the nanocomposite have a significantly reduced thermal quenching energy relative to that of bare ZnS/Mn2+ nanoparticles. In addition, between room temperature and 90 degreesC, the luminescence of the ZnS/Mn2+ nanoparticles at 596 nm increases in intensity with increasing temperature. This surprising phenomenon is attributed to thermoluminescence and thermal curing of the particle surface upon heating.
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| 9. |
- Chen, W, et al.
(författare)
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Size dependence of Eu2+ fluorescence in ZnS:Eu2+ nanoparticles
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89:5, s. 2671-2675
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Tidskriftsartikel (refereegranskat)abstract
- The emission bands of the 4.2, 3.2 and 2.6 nm sized ZnS:Eu2+ nanoparticles are peaking at 670, 580 and 520 nm, respectively. The emission of the 4.2 nm sized nanoparticles originates from the recombination of the Eu2+-bound exciton, while the emission of the 3.2 and 2.6 nm sized nanoparticles is from the Eu2+ intra-ion transition of 4f(6)5d(1)(t(2g))-4f(7). Possible mechanisms for the size dependence of the 4f(6)5d(1)(t(2g))-4f(7) transition of Eu2+ in ZnS:Eu2+ nanoparticles were investigated, and it was concluded that the decreases in the electron-phonon coupling and in crystal field strength upon a decrease in size are the two major factors responsible for the shift. (C) 2001 American Institute of Physics.
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| 10. |
- Chen, W, et al.
(författare)
-
Structure, luminescence, and dynamics of Eu2O3 nanoparticles in MCM-41
- 2002
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 106:28, s. 7034-7041
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Tidskriftsartikel (refereegranskat)abstract
- The structure, luminescence spectroscopy, and lifetime decay dynamics of Eu2O3 nanoparticles formed in MCM-41 have been investigated. Both X-ray diffraction and high-resolution transmission electron microscopic observations indicate that Eu2O3 nanoparticles of monoclinic structure are formed inside channels of MCM-41 by heating at 140 degreesC. However, heat treatment at 600 or 700 degreesC causes migration of Eu2O3 from the MCM-41 channels, forming nanoparticles of cubic structure outside the MCM-41 channels. After heating to 900 degreesC, some of the cubic Eu2O3 particles change to monoclinic Eu2O3, and the MCM-41 structure breaks down and a different or disordered phase is formed. The feature of the hypersensitive D-5(0) --> F-7(2) emission profile of Eu3+ is used to follow the structural changes. In the luminescence spectrum of the sample prepared at 140 degreesC, the emission spectrum is dominated by peaks at 615 and 623 nm, while in the other samples a peak at 612 nm is prevalent. Photoluminescence lifetimes show the existence of short (<1 mus) and long (microsecond to millisecond) components for each sample. The fast decay is attributed to quenching by surface states of the nanoparticles or energy transfer to the MCM-41, while the longer time decays show the effects of concentration quenching. The monoclinic sample prepared at 140 degreesC shows a higher luminescence intensity than the cubic samples or the bulk powder. These observations indicate that MCM-41 as a template can be used for making and stabilizing monoclinic rare earth oxides, which normally are stable only at high temperatures and high pressures. More importantly, the nanophase Eu2O3/MCM-41 composite materials formed at low temperatures might represent a new type of efficient luminescence material with fast response, with potential applications in lighting and displays.
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| 11. |
- Chen, W, et al.
(författare)
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Temperature and pressure dependences of the Mn2+ and donor-acceptor emissions in ZnS : Mn2+ nanoparticles
- 2002
-
Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 92:4, s. 1950-1955
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Tidskriftsartikel (refereegranskat)abstract
- Temperature and pressure dependent measurements have been performed on 3.5 nm ZnS:Mn2+ nanoparticles. As temperature increases, the donor-acceptor (DA) emission of ZnS:Mn2+ nanoparticles at 440 nm shifts to longer wavelengths while the Mn2+ emission (T-4(1)-(6)A(1)) shifts to shorter wavelengths. Both the DA and Mn2+ emission intensities decrease with temperature with the intensity decrease of the DA emission being much more pronounced. The intensity decreases are fit well with the theory of thermal quenching. As pressure increases, the Mn2+ emission shifts to longer wavelengths while the DA emission wavelength remains almost constant. The pressure coefficient of the DA emission in ZnS:Mn2+ nanoparticles is approximately -3.2 meV/GPa, which is significantly smaller than that measured for bulk materials. The relatively weak pressure dependence of the DA emission is attributed to the increase of the binding energies and the localization of the defect wave functions in nanoparticles. The pressure coefficient of Mn2+ emission in ZnS:Mn2+ nanoparticles is roughly -34.3 meV/GPa, consistent with crystal field theory. The results indicate that the energy transfer from the ZnS host to Mn2+ ions is mainly from the recombination of carriers localized at Mn2+ ions. (C) 2002 American Institute of Physics.
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| 12. |
- Chen, W, et al.
(författare)
-
The origin of x-ray luminescence from CdTe nanoparticles in CdTe/BaFBr : Eu2+ nanocomposite phosphors
- 2006
-
Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 99:3
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray luminescence from CdTe nanoparticles is observed when CdTe nanoparticles are encapsulated into BaFBr:Eu2+ phosphors. In contrast, negligible x-ray luminescence is observed from the unencapsulated nanoparticles, either in solution or in solid form. The origin of the x-ray luminescence is attributed to the effective energy transfer from Eu2+ ions to CdTe nanoparticles in the nanocomposite materials. The x-ray luminescence of these nanocomposites is dose dependent and the emission wavelength is size adjustable which may allow use as a type of dosimeter for both in vitro and in vivo applications. (c) 2006 American Institute of Physics.
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| 13. |
- Chen, W, et al.
(författare)
-
Upconversion luminescence of Eu3+ and Mn2+ in ZnS : Mn2+, Eu3+ codoped nanoparticles
- 2004
-
Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 95:2, s. 667-672
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Tidskriftsartikel (refereegranskat)abstract
- Strong upconversion luminescence of both Mn2+ and Eu3+ is observed in ZnS:Mn2+, Eu3+ codoped nanoparticles. Laser power dependencies and spectroscopic data show that the upconversion emission is due to two-photon excitation of each specific dopant ion. The relative differences in two-photon excitation cross section result in different relative intensities for the Eu3+ and Mn2+ upconversion at different wavelengths. Spectroscopic data and luminescence lifetime data indicate no evidence of energy transfer between the Mn2+ and Eu3+ ions. (C) 2004 American Institute of Physics.
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| 14. |
- Deppert, Knut, et al.
(författare)
-
Aerosol fabrication of nanocrystals of InP
- 1999
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Ingår i: Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers. - 0021-4922. ; 38:2 B, s. 1056-1059
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystals of indium phosphide, with diameters of around 10nm, have been produced via an aerosol route. The method is based on the formation of monodisperse indium droplets and the subsequent reaction with phosphine at elevated temperature. The size of the final InP nanocrystal is self-limited by the size of the introduced size-selected In droplet. This size can be tuned carefully, thus this method allows a narrow size distribution of the nanocrystals. The kinetics of the reaction of In to produce InP depends on the temperature and the phosphine flow. Extensive high resolution transmission electron microscopy studies lead to a consistent picture of the process. Our approach opens the possibility for efficient production of size-selected semiconductor nanocrystals and it will allow new types of self-assembly and control of quantum dots.
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| 15. |
- Deppert, Knut, et al.
(författare)
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Size-selected nanocrystals of III-V semiconductor materials by the aerotaxy method
- 1998
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Ingår i: Journal of Aerosol Science. - 0021-8502. ; 29:5-6, s. 737-748
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a fabrication route to produce size-selected III-V semiconductor nanocrystals via a simple, reliable, and efficient aerosol route. Since this approach includes the reaction of aerosol particles and a self-organized growth of a new compound, all in the aerosol phase, we call this process aerotaxy. Size-selected nanocrystals of different III-V compounds in a diameter range below 20 nm were fabricated using this method. Through the reaction of arsine with gallium droplets or of phosphine with indium droplets, GaAs and InP clusters were formed. Our approach opens the possibility to produce contamination-free and size-selected nanocrystals of compound semiconductor materials with considerable freedom in composition and size.
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| 16. |
- Joly, A G, et al.
(författare)
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Upconversion luminescence of CdTe nanoparticles
- 2005
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 71:16, s. 1-165304
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Tidskriftsartikel (refereegranskat)abstract
- Efficient upconversion luminescence is observed from CdTe nanoparticles in solution and precipitated as solids. In the solids, the upconversion luminescence spectrum is significantly red shifted relative to the photoluminescence spectrum, whereas in solution, there is very little spectral shift. The upconversion luminescence exhibits a near-quadratic laser power dependence, both at room temperature and at 10 K. Both the upconversion and photoluminescence show similar decay dynamics with the solid samples showing shorter lifetimes compared to the solutions. This lifetime shortening is attributed to surface-state quenching. These results indicate that two-photon excitation is the likely upconversion excitation mechanism in these particles and that phonon-populated trap states do not contribute to the upconversion.
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| 17. |
- Magnusson, Martin H., et al.
(författare)
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Gold nanoparticles : Production, reshaping, and thermal charging
- 1999
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Ingår i: Journal of Nanoparticle Research. - 1388-0764. ; 1:2, s. 243-251
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Tidskriftsartikel (refereegranskat)abstract
- Gold nanoparticles are of great interest for various nanoelectronic applications, e.g., for making single electron transistors or very fine leads to molecular size entities. For this and other applications, it is important that all particles have controllable size and shape. In this paper, we describe the production of size-selected gold aerosol particles in the 20 nm range made by evaporation in a high-temperature tube furnace and subsequent size selection. To obtain spherical particles, it was necessary to reshape the particles at high temperature, which was investigated for temperatures between 25°C and 1200°C. High-resolution transmission electron microscopy showed that the degree of crystallinity became higher for higher reshaping temperature. During reshaping at high temperature, an anomalous charging behavior was discovered, whereby negatively as well as positively charged particles became multiply negatively charged. Possible mechanisms for explaining this thermally activated phenomenon are discussed.
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| 18. |
- Oku, Takeo, et al.
(författare)
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Digital HREM imaging of yttrium atoms in YB56 with YB66 structure
- 1998
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596. ; 135:2, s. 182-193
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Tidskriftsartikel (refereegranskat)abstract
- The arrangement of yttrium atoms in YB56with YB66structure was determined by high-resolution electron microscopy (HREM) using a slow-scan CCD camera. Digital HREM images recorded along the [100], [110], and [111] directions of the YB56crystals showed "averaged" yttrium atom positions in the boron clusters, which were also confirmed by image simulation. Digital HREM images recorded from thin regions (
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| 19. |
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| 20. |
- Arve, K, et al.
(författare)
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Analysis of the state and size of silver on alumina in effective removal of NOx from oxygen rich exhaust gas
- 2006
-
Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 0000-0000. ; 6:4, s. 1076-1083
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Tidskriftsartikel (refereegranskat)abstract
- Ag/alumina catalysts with different silver contents for octane-SCR were prepared by impregnation and incipient wetness methods. Activity tests revealed that the decisive factor for high activity is not only a high dispersion of silver, but also the ability of the system to redisperse clustered silver. Determination of dispersion by TEM/HAADF and O-2-chemisorption experiments resulted in values close to each other even if the results were not directly comparable. This is suggested to be due to not complete silver reduction below 700 degrees C and the samples being very heterogeneous in terms of particle size, e.g., having a bimodal size distribution. Small charged Ag-n(delta+) clusters containing 2-8 silver atoms highly prevailed in the samples containing < 2 wt% Ag and exhibiting high octane-SCR activity In highly loaded Ag/alumina samples or those reduced and reoxidized at high temperature (> 400 degrees C), large metallic particles are stabilized, resulting in poor conversion of NOx to N-2.
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| 21. |
- Arve, K, et al.
(författare)
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Structure-activity relationship in HC-SCR of NOx, by TEM, O-2-chemisorption, and EDXS study of Ag/Al2O3
- 2006
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 110:1, s. 420-427
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Tidskriftsartikel (refereegranskat)abstract
- Ag/alumina catalysts with different silver loading (1.28 - 6 wt %) for lean NO reduction activity were prepared by impregnation and the incipient wetness method. Complementary HRTEM, HAADF, O-2-chemisorption, and EDXS studies were applied to investigate the dependence between silver particle size and catalytic activities of the prepared materials. The catalyst with the lowest silver loading (1.28 wt %) was found to be the most active catalyst in terms of reacted NO molecules per mole of silver. On the basis of the HRTEM, HAADF, and O-2-chemisorption studies it could be concluded that the mean particle size or particle size distribution of the samples alone could not explain the big difference in the activities. EDXS analyses showed on the other hand that all of the samples were very heterogeneous in terms of particle size distribution, e.g., including both small and very big particles. Furthermore, both metallic silver and mainly hexagonal silver oxide (Ag2O) were found to be present in the samples. Despite the valuable information provided by ex situ characterization of the prepared samples, it needs to be emphasized that establishing a structure-reactivity relationship for this type of catalyst requires in situ characterization.
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| 22. |
- Borg, S, et al.
(författare)
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Structure study of Bi2.5Na0.5Ta2O9 and B2.5Nam-1.5NbmO3m+3 (m=2-4) by neutron powder diffraction and electron microscopy
- 2002
-
Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596. ; 167:1, s. 86-96
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structures of Bi2.5Na0.5Ta2O9 and Bi2.5Nam-1.5NbmO3m+3 (m = 3,4) have been investigated.ysis of their neutron powder diffraction by the Rietveld anal patterns (lambda = 1.470 Angstrom). These compounds belong to the Aurivillius phase family and are built up by (Bi2O2)(2+) fluorite layers and (A(m-1)BnO(3m+1))(2-) (m = 2-4) pseudo-perovskite slabs. Bi2.5Na0.5Ta2O9 (m = 2) and Bi2.5Na2.5Nb4O15 (m = 4) crystallize in the orthorhombic space group A2(1)am, Z = 4, with lattice constants of a = 5.4763(4), b = 5.4478(4), c 24.9710 (15) and a = 5.5095(5), b = 5.4783(5), c = 40.553(3) Angstrom, respectively. Bi2.5Na1.5Nb3O12 (m = 3) has been refined in the orthorhombic space group B2cb, Z = 4, with the unit-cell parameters a = 5.5024(7), b = 5.4622(7), and c = 32.735(4) Angstrom. In comparison with its isostructural Nb analogue, the structure of Bi2.5Na0.5Ta2O9 is less distorted and bond valence sum calculations indicate that the Ta-O bonds are somewhat stronger than the Nb-O bonds. The cell parameters a and h increase with increasing m for the compounds Bi2.5Nam-1.5NbmO3m+3 (m = 2-4), causing a greater strain in the structure. Electron microscopy studies verify that the intergrowth of mixed perovskite layers, caused by stacking faults, also increases with increasing m. (C) 2002 Elsevier Science (USA).
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| 23. |
- Chen, W, et al.
(författare)
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Fabrication and luminescence of ZnS : Mn2+ nanoflowers
- 2005
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 0000-0000. ; 5:9, s. 1309-1322
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Tidskriftsartikel (refereegranskat)abstract
- Visually striking nanoflowers composed of ZnS:Mn2+ nanoparticles are prepared and characterized. The configurations of these fractal structures are very sensitive to both the pH values of the particle solutions from which they are precipitated and the substrates on which they are deposited. At pH 2.2, the fractal structures resemble trees without leaves; at pH 7.7, they are tree-like with four arms and at pH 11.0 they resemble trees with six arms. High resolution transmission microscopy reveals that the nanoflowers are composed of ZnS:Mn2+ nanoparticles of 2-5 nm in size. X-ray photoelectron spectral data indicate that the sample compositions of nitrogen, chlorine, and sulfur vary gradually with pH values of the solutions. These changes may have an impact on both the fractal configuration and the luminescence properties. The emission spectra of the particle solutions at pH values of 2.2 and 11.0 are similar with the emission maximum at 475 nm. As the pH value approaches 7.7, the emission spectral maximum shifts to longer wavelengths. At a pH value of 7.7, the emission peak wavelength is the reddest, 520 nm. The emission peak of the nanoflowers at a pH value of 9.3 is 510 nm, while the emission spectrum of the nanoflowers at 5.2 has two peaks at 500 nm and 440 nm, respectively. These blue-green emissions are attributed to defects and are the dominant luminescence from the nanoflowers. The emission from Mn2+ dopant is only observed in the delayed spectra of the fractal solid samples.
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| 24. |
- Chen, W, et al.
(författare)
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Full-color emission from In2S3 and ln(2)S(3): Eu3+ nanoparticles
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:32, s. 11927-11934
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Tidskriftsartikel (refereegranskat)abstract
- New observations on the luminescence Of In2S3 and europium-doped In2S3 nanoparticles show a green (5 10 nm) emission from In2S3 and In1.8Eu0.2S3 nanoparticles while a blue (425 nm) emission is observed from ln(1.6)Eu(0.4)S(3) nanoparticles. Both the blue and green emissions have large Stokes shifts of 62 and 110 nm, respectively. Excitation with longer-wavelength photons causes the blue emission to shift to a longer wavelength while the green emission wavelength remains unchanged. The lifetimes of both the green and blue emissions are similar to reported values for excitonic recombination. When doped with Eu3+, in addition to the broad blue and green emissions, a red emission near 615 nm attributed to Eu3+ is observed. Temperature dependences on nanoparticle thin films indicate that with increasing temperature, the green emission wavelength remains constant, however, the blue emission shifts toward longer wavelengths. Based on these observations, the blue emission is attributed to exciton recombination and the green emission to Indium interstitial defects. These nanoparticles show full-color emission with high efficiency, fast lifetime decays, and good stability; they are also relatively simple to prepare, thus making them a new type of phosphor with potential applications in lighting, flat-panel displays, and communications.
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| 25. |
- Chen, W, et al.
(författare)
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Utilizing nanofabrication to construct strong, luminescent materials
- 2006
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 17:10, s. 2595-2601
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Tidskriftsartikel (refereegranskat)abstract
- Luminescent materials have been utilized widely in applications from lighting to sensing. The new development of technologies based on luminescence requires the materials to have high luminescence efficiency and mechanical strength. In this paper, we report the fabrication of luminescent materials possessing high mechanical strength by nanofabrication with polyvinyl alcohol used as a stabilizer or coupling agent. X-ray diffraction and high-resolution transmission microscope observations reveal that the nanocomposite sample contains ZnS and ZnO nanoparticles as well as kozoite and sodium nitrate. The mechanical strength and hardness of these nanocomposites are reasonably high, higher than polycarbonate and some carbon nanotube reinforced nanocomposites. Strong luminescence is observed in the new nanocomposites and the luminescence intensity does not degrade following up to 30 min of x-ray irradiation. Our results indicate that nanofabrication may provide a good method to improve the mechanical strength of luminescent materials for some applications in which high-strength luminescent materials are needed.
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