Time-resolved stimulated emission spectroscopy was employed to probe the local environment of DASPMI (<i>4-(4-(dimethylamino)styryl)-N-methyl-pyridinium iodide</i>) in binary solvents of different viscosity and in a sol-gel matrix. DASPMI is one of the molecules of choice to probe local environments, and the dependence of its fluorescence emission decay on viscosity has been previously used for this purpose in biological samples, solid matrices as well as in solution. The results presented in this paper show that time-resolved stimulated emission of DASPMI is a suitable means to probe the viscosity of local environments. Having the advantage of a higher time resolution, stimulated emission can provide information that is complementary to that obtained from fluorescence decay measurements, making it feasible to probe systems with lower viscosity.

Ana Rei

Graham Hungerford

Michael Belsley

M. Isabel C. Ferreira

Peter Schellenberg

Probing Local Environments by Time-Resolved Stimulated Emission Spectroscopy

Chromium(VI) salts are possible contaminants of the chromium(III) pigments used as colorants in eyeshadow preparations. The use of products containing these contaminants poses acute risks for sensitization and contact allergies. Chromium(VI) compounds are also classified as carcinogenic to humans (IARC group 1). An analytical method to analyse trace levels of chromium(VI) in eyeshadow was developed in this study. The method is based on an extraction of the chromium(VI) from the sample using a maximum extraction with alkali and additionally with synthetic lachrymal fluid to simulate physiological conditions. Following derivatization with 1,5-diphenylcarbazide, the extracted chromium(VI) is then quantified by spectrophotometry (540&#x2009;nm). Validation tests indicated a method standard deviation (inter- and intraday) of 8.7% and a linear range up to 25&#x2009;mg/kg. The average recovery was 107.9%, and the detection limit was 2.7&#x2009;mg/kg. The applicability of the procedure was confirmed by the analysis of pigments and authentic eyeshadow matrices.

Sarah Wurster

Evamaria Kratz

Dirk W. Lachenmeier

Gerd Mildau

Spectrophotometric Quantification of Toxicologically Relevant Concentrations of Chromium(VI) in Cosmetic Pigments and Eyeshadow Using Synthetic Lachrymal Fluid Extraction

Santanu Bera

Sandip Dhara

Alexander Milekhin

M. W. Chu

S. M. Shivaprasad

Spectroscopic and Structural Insight into the Size-Dependent Behavior of the Nanophase

We review recent experimental work to utilize the size dependence of the luminescence quenching of colloidal semiconductor quantum dots induced by functionalized porphyrin molecules attached to the surface to describe a photoluminescence (PL) quenching process which is different from usual models of charge transfer (CT) or Foerster resonant energy transfer (FRET). Steady-state and picosecond time-resolved measurements were carried out for nanocomposites based on colloidal CdSe/ZnS and CdSe quantum dots (QDs) of various sizes and surfacely attached tetra-mesopyridyl-substituted porphyrin molecules (&#x201c;Quantum Dot-Porphyrin&#x201d; nanocomposites), in toluene at 295&#x2009;K. It was found that the major part of the observed strong quenching of QD PL in &#x201c;QD-Porphyrin&#x201d; nanocomposites can neither be assigned to FRET nor to photoinduced charge transfer between the QD and the chromophore. This PL quenching depends on QD size and shell and is stronger for smaller quantum dots: QD PL quenching rate constants <svg style="vertical-align:-4.74141pt;width:14.6625px;" id="M1" height="16.475" version="1.1" viewBox="0 0 14.6625 16.475" width="14.6625"  xmlns="http://www.w3.org/2000/svg">
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</svg> scale inversely with the QD diameter. Based on the comparison of experimental data and quantum mechanical calculations, it has been concluded that QD PL quenching in &#x201c;QD-Porphyrin&#x201d; nanocomposites can be understood in terms of a tunneling of the electron (of the excited electron-hole pair) followed by a (self-) localization of the electron or formation of trap states. The major contribution to PL quenching is found to be proportional to the calculated quantum-confined exciton wave function at the QD surface. Our findings highlight that single functionalized molecules can be considered as one of the probes for the complex interface physics and dynamics of colloidal semiconductor QD.

Eduard I. Zenkevich

Thomas Blaudeck

Christian von Borczyskowski

Size-Dependent Non-FRET Photoluminescence Quenching in Nanocomposites Based on Semiconductor Quantum Dots CdSe/ZnS and Functionalized Porphyrin Ligands

A series of samples with quaternary CdS<inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow /><mml:mrow><mml:mn>1</mml:mn><mml:mo>&#x2212;</mml:mo><mml:mi>x</mml:mi><mml:mo>&#x2212;</mml:mo><mml:mi>y</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula>Se<inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow /><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>Te<inline-formula><mml:math id="M3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow /><mml:mi>y</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> nanocrystals with cations of three types distributed over nanocrystal lattice sites were grown in a borosilicate glass matrix by the diffusion-limited growth technique. Their Raman spectra confirm the three-mode compositional behaviour of CdS<inline-formula><mml:math id="M4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow /><mml:mrow><mml:mn>1</mml:mn><mml:mo>&#x2212;</mml:mo><mml:mi>x</mml:mi><mml:mo>&#x2212;</mml:mo><mml:mi>y</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula>Se<inline-formula><mml:math id="M5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow /><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>Te<inline-formula><mml:math id="M6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow /><mml:mi>y</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> phonon spectra. The compositional dependence of the LO phonon frequencies is analysed experimentally for a series of samples containing nanocrystals with <inline-formula><mml:math id="M7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>x</mml:mi><mml:mo>&#x2248;</mml:mo><mml:mi>y</mml:mi></mml:math></inline-formula>.

Yuriy M. Azhniuk

Yuriy I. Hutych

Vasyl V. Lopushansky

Mykola V. Prymak

Alexander V. Gomonnai

Dietrich R. T. Zahn

Raman Spectra of Quaternary CdS<sub><i>1&#x2212;x&#x2212;y</i></sub>Se<sub><i>x</i></sub>Te<sub><i>y</i></sub> Nanocrystals Embedded in Borosilicate Glass

ZnO nanorods prepared through chemical vapor deposition technique are characterized by microscopic and X-ray photoelectron spectroscopy (XPS) techniques to correlate the effects of size on the binding energy of Zn 2p<sub>3/2</sub> photoelectrons. A positive shift in Zn 2p<sub>3/2</sub>-binding energy as compared to that in bulk ZnO is assumed to be the effect of size of ZnO tips. The shift in binding energy has been explained in terms of relaxation energy in the photoemission process. Simultaneously, Auger parameter of the nanorods is evaluated for stoichiometric composition. The extra peak in O1s spectrum of nanorods is explained as adsorbed O-bearing species or surface contaminants.

S. Velmurugan

A. K. Tyagi

Analysis on Binding Energy and Auger Parameter for Estimating Size and Stoichiometry of ZnO Nanorods

Well-dispersed Ag nanoparticles with size of 20&#x2013;30&#x2009;nm were synthesized in water at room temperature with a self-made novel imidazoline Gemini surfactant quaternary ammonium salt of di (2-heptadecyl-1-formyl aminoethyl imidazoline) hexanediamine. Transmission electron microscopy, X-ray powder diffraction, ultraviolet-visible absorption spectra, and Fourier transform infrared ray were used to characterize the Ag nanoparticles. Results showed that the micellized aggregation of imidazoline Gemini surfactant in water, the growth of Ag initial particles, and the interaction (adsorption and coordination) between surfactant and Ag<sup>+</sup>/Ag nanoparticles took place simultaneously to form the well-dispersed Ag nanoparticles. Catalytic results show that the surface-modified Ag product was an active metal catalyst for methyl orange reduction reaction due to the effective adsorption between Ag nanoparticles and methyl orange molecules, which was of promising application in environmental protection.

Weihua Li

Congtao Sun

Baorong Hou

Xiaodong Zhou

Room Temperature Synthesis and Catalytic Properties of Surfactant-Modified Ag Nanoparticles

Vibrational properties of hydrogenated silicon-rich nitride (<svg style="vertical-align:-3.21404pt;width:46.712502px;" id="M1" height="14.8" version="1.1" viewBox="0 0 46.712502 14.8" width="46.712502"  xmlns="http://www.w3.org/2000/svg">
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</svg>) of various stoichiometry (<svg style="vertical-align:-1.29163pt;width:86.574997px;" id="M2" height="12.425" version="1.1" viewBox="0 0 86.574997 12.425" width="86.574997"  xmlns="http://www.w3.org/2000/svg">
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</svg>) and hydrogenated amorphous silicon (<svg style="vertical-align:-0.17554pt;width:40.9375px;" id="M3" height="11.0125" version="1.1" viewBox="0 0 40.9375 11.0125" width="40.9375"  xmlns="http://www.w3.org/2000/svg">
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</svg>) films were studied using Raman spectroscopy and Fourier transform infrared spectroscopy. Furnace annealing during 5 hours in Ar ambient at <svg style="vertical-align:-0.17555pt;width:46.262501px;" id="M4" height="11.0375" version="1.1" viewBox="0 0 46.262501 11.0375" width="46.262501"  xmlns="http://www.w3.org/2000/svg">
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 and pulse laser annealing were applied to modify the structure of films. Surprisingly, after annealing with such high-thermal budget, according to the FTIR data, the nearly stoichiometric silicon nitride film contains hydrogen in the form of Si&#x2013;H bonds. From analysis of the FTIR data of the Si&#x2013;N bond vibrations, one can conclude that silicon nitride is partly crystallized. According to the Raman data <svg style="vertical-align:-0.17554pt;width:40.9375px;" id="M5" height="11.0125" version="1.1" viewBox="0 0 40.9375 11.0125" width="40.9375"  xmlns="http://www.w3.org/2000/svg">
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</svg> films with hydrogen concentration 15&#x25; and lower contain mainly Si&#x2013;H chemical species, and films with hydrogen concentration 30&#x2013;35&#x25; contain mainly Si&#x2013;H<sub  >2</sub> chemical species. Nanosecond pulse laser treatments lead to crystallization of the films and its dehydrogenization.

Kirill O. Bugaev

Anastasia A. Zelenina

Vladimir A. Volodin

Vibrational Spectroscopy of Chemical Species in Silicon and Silicon-Rich Nitride Thin Films

Resonant Raman spectroscopy has been employed to explore the first- and higher-order phonon spectra of several kinds of II-VI nanocrystals (NCs), with the aim of better understanding of the nature of phonon modes and forming a unified view onto the vibrational spectrum of semiconductor NCs. Particularly, besides the previously discussed TO, SO, LO, and 2LO modes, the combinational modes of TO+LO and SO+LO can be assumed to account for the lineshape of the spectrum below 2LO band. No trace of 2TO or 2SO band was detected, what can be the result of the dominance of Fröhlich mechanism in electron-phonon coupling in II-VI compounds. The resonant phonon Raman spectrum of NCs smaller than 2 nm is shown to be dominated by a broad feature similar to the SO mode of larger NCs or phonon density of states of a bulk crystal.

Volodymyr Dzhagan

Mykhailo Valakh

Nikolai Mel'nik

Olexandra Rayevska

Irina Lokteva

Joanna Kolny-Olesiak

Phonon Spectra of Small Colloidal II-VI Semiconductor Nanocrystals

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International Journal of Spectroscopy - Table of contents 2012

International Journal of Spectroscopy | Hindawi

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