SrO:Mn as EPR Marker and Intensity Standard

Rosenthal, Jenny E.; Yarmus, L.

doi:10.1063/1.1720196

Cited by 27 publications

(12 citation statements)

References 1 publication

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“…Samples were checked for background EPR signals before and after illumination. The g factors were calibrated for homogeneity and accuracy by comparison to a Mn 2+ standard in a SrO matrix ( g = 2.0012 ± 0.0002) and by using coal samples with g = 2.00285 ± 0.00005, respectively.…”

Section: Methodsmentioning

confidence: 99%

Surface Restructuring of Nanoparticles: An Efficient Route for Ligand−Metal Oxide Crosstalk

et al. 2002

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Surface modification of nanocrystalline metal oxide particles with enediol ligands was found to result in altered optical properties of nanoparticles. The surface modification results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites. The optical shift is correlated to the dipole moment of the Ti-ligand complexes at the particle surface and decreases with the ligand size. The binding was found to be exclusively characteristic of colloids in the nanocrystalline domain(<20 nm). X-ray near-edge structure measurements at Ti K edge indicate that in this size domain the surface Ti atoms adjust their coordination environment to form undercoordinated sites. These five-coordinated defect sites are the source of novel enhanced and selective reactivity of the nanoparticle toward bidentate ligand binding as observed using IR spectroscopy. Enediol ligands have the optimal geometry for chelating surface Ti atoms, resulting in a five-membered ring coordination complex and restored six-coordinated octahedral geometry of surface Ti atoms. The binding of enediol ligands is enhanced because of the stability gained from adsorption-induced restructuring of the nanoparticle surface. Consistent behavior was found for the three different nanocrystalline metal oxide systems: TiO 2 , Fe 2 O 3 , and ZrO 2 .

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Section: Methodsmentioning

confidence: 99%

Surface Restructuring of Nanoparticles: An Efficient Route for Ligand−Metal Oxide Crosstalk

et al. 2002

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“…The sample was equilibrated for 20 min at the specified temperature before the spectrum was recorded at the temperature indicated on the figure. The g factors were calibrated by comparison to a Mn 2+ standard in a SrO matrix (g ) 2.0012 ( 0.0002) 11 and with a 1,1-diphenyl-2-picrylhydrazyl (DPPH) standard (g ) 2.0036 ( 0.0003). A high concentration of particles (concentration of particles 10 -5 -10 -4 M) in 2,2,4-trimethylpentane solution and 0.05% TOPO that formed an optically clear organic glass at cryogenic temperatures was used to improve the quality of detection, as described previously.…”

Section: Methodsmentioning

confidence: 99%

Electron and Hole Adducts Formed in Illuminated InP Colloidal Quantum Dots Studied by Electron Paramagnetic Resonance

et al. 2002

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An electron paramagnetic resonance (EPR) study of photoexcited colloidal InP quantum dots (QD) shows the formation of electron and hole adducts. An EPR signal at g ) 0.58 is assigned to a nonradiative hole trap that does not form immediately upon illumination, but forms only after the illuminated sample ages and becomes stabilized at room temperature; it then becomes permanent at the InP QD surface. This signal completely disappears upon electron injection into the QD from a reducing agent (sodium biphenyl). Light immediately quenches the signal at g ) 0.58, and it re-forms reversibly when the light is turned off. A signal at g ) 2.055 is assigned to electron surface traps, and it appears in nonetched QD samples; it completely disappears after etching with HF. A signal at g ) 2.001 has a very narrow line width and is assigned to delocalized mobile holes that are located in the QD core. A defect model for InP QDs is proposed based on the EPR results reported here plus results from optically detected magnetic resonance experiments reported separately.

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“…Samples were checked for background EPR signals before irradiation. The g -factors were calibrated by comparison to a Mn 2+ standard in SrO matrix ( g = 2.0012 ± 0.0002) . Lead ions were added as Pb(CH 3 COO) 2 .…”

Section: Methodsmentioning

confidence: 99%

“…The g-factors were calibrated by comparison to a Mn 2+ standard in SrO matrix (g ) 2.0012 ( 0.0002). 13 Lead ions were added as Pb(CH 3 COO) 2 . FTIR: Measurements were performed on a Nicolet 510 Fourier transform infrared spectrometer equipped with a Spectra-Tech Inc. diffuse reflectance accessory.…”

Section: Tio 2 98mentioning

confidence: 99%

Surface Modification of Small Particle TiO₂ Colloids with Cysteine for Enhanced Photochemical Reduction: An EPR Study

et al. 1996

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Surface complexation of colloidal titanium dioxide nanoparticles (40−60 Å) with cysteine was investigated by electron paramagnetic resonance (EPR) and infrared (diffuse reflectance infrared Fourier transform−DRIFT) spectroscopies. Cysteine was found to bind strongly to the TiO2 surface, resulting in formation of new trapping sites where photogenerated electrons and holes are localized. Illumination of cysteine-modified TiO2 at 77 K resulted in formation of cysteine radicals with the unpaired electron localized on the carboxyl group. Upon warming to 150 K, these radicals are transformed into sulfur-centered radicals as observed by EPR spectroscopy. We have demonstrated the existence of two surface Ti(III) centers on cysteine-modified TiO2 particles having different extents of tetragonal distortion of the octahedral crystal field. Upon addition of lead ions, a new complex of cysteine that bridges surface titanium atoms and lead ions was detected by IR spectroscopy. Illumination of lead/cysteine-modified TiO2 did not result in the formation of sulfur-centered radicals. Instead, a symmetrical, lattice defect type EPR signal for trapped holes was observed. Addition of methanol to this system resulted in the formation of a ·CH2OH radical at 8.2 K. After the temperature was raised to 120 K, doubling of the signal associated with electrons trapped at the particle surface (Ti(III)surf) was observed. On further increase of the temperature to 200 K, the EPR signal for trapped electrons disappeared due to the reduction of Pb2+ ions, and metallic lead precipitated at room temperature. Conversion of photogenerated holes in the presence of methanol into trapped electrons can lead to the doubled quantum efficiency of metallic lead precipitation.

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SrO:Mn as EPR Marker and Intensity Standard

Cited by 27 publications

References 1 publication

Surface Restructuring of Nanoparticles: An Efficient Route for Ligand−Metal Oxide Crosstalk

Surface Restructuring of Nanoparticles: An Efficient Route for Ligand−Metal Oxide Crosstalk

Electron and Hole Adducts Formed in Illuminated InP Colloidal Quantum Dots Studied by Electron Paramagnetic Resonance

Surface Modification of Small Particle TiO₂ Colloids with Cysteine for Enhanced Photochemical Reduction: An EPR Study

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SrO:Mn as EPR Marker and Intensity Standard

Cited by 27 publications

References 1 publication

Surface Restructuring of Nanoparticles: An Efficient Route for Ligand−Metal Oxide Crosstalk

Surface Restructuring of Nanoparticles: An Efficient Route for Ligand−Metal Oxide Crosstalk

Electron and Hole Adducts Formed in Illuminated InP Colloidal Quantum Dots Studied by Electron Paramagnetic Resonance

Surface Modification of Small Particle TiO2 Colloids with Cysteine for Enhanced Photochemical Reduction: An EPR Study

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Surface Modification of Small Particle TiO₂ Colloids with Cysteine for Enhanced Photochemical Reduction: An EPR Study