The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Michael Grätzel - One of the best experts on this subject based on the ideXlab platform.
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Photoinduced processes in lead iodide perovskite solid-state solar cells
Physical Chemistry of Interfaces and Nanomaterials XII, 2013Co-Authors: Arianna Marchioro, Michael Grätzel, Jan C. Brauer, Joël Teuscher, Jacques-e. MoserAbstract:Organic-inorganic hybrid systems based on lead halide compounds have recently encountered considerable success as light absorbers in solid-state solar cells. Herein we show how fundamental mechanistic processes in Mesoporous Oxide films impregnated with CH3NH3PbI3 can be investigated by time resolved techniques. In particular, charge separation reactions such as electron injection into the titanium diOxide film and hole injection into the hole transporting material spiro-OMeTAD as well as the corresponding charge recombination reactions were scrutinized. Femtosecond transient absorption spectroscopy and time-resolved terahertz spectroscopy were applied to CH3NH3PbI3 deposited either on TiO2 or Al2O3 Mesoporous films and infiltrated with the hole transporting material spiro-OMeTAD.
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highly selective and reversible optical colorimetric and electrochemical detection of mercury ii by amphiphilic ruthenium complexes anchored onto Mesoporous Oxide films
Advanced Functional Materials, 2006Co-Authors: Mohammad Khaja Nazeeruddin, Robin Humphrybaker, Davide Di Censo, Michael GrätzelAbstract:The colorimetric, fluorimetric, and electrochemical detection of mercury ions by functionalized ruthenium sensitizers in aqueous and non-aqueous solutions and on anchored TiO2 films are investigated. Mercury ions coordinate reversibly to the ruthenium sensitizers, inducing a color change and increasing the phosphorescence intensity significantly. The electrochemical data of the adsorbed sensitizer on TiO2 films show a reversible couple, owing to the percolation through electronic couplings between –NCS ligands of neighboring molecules; upon exposure to a Hg2+-containing solution, the electrical signal is appreciably reduced. The detection limit for mercury(II) ions using UV-vis spectroscopy in homogeneous aqueous solutions is estimated to be ∼ 20 ppb. The results presented herein have important implications in the development of reversible colorimetric, fluorimetric, and electrochemical on–off sensors based on nanocrystalline semiconductor films for the simple, swift, and selective detection of mercury ions in solution.
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Sol-Gel Processed TiO2 Films for Photovoltaic Applications
Journal of Sol-Gel Science and Technology, 2001Co-Authors: Michael GrätzelAbstract:The dye sensitized solar cells (DYSC) provides a technically and economically credible alternative concept to present day p-n junction photovoltaic devices. In contrast to the conventional systems where the semiconductor assumes both the task of light absorption and charge carrier transport the two functions are separated here. Light is absorbed by a sensitizer which is anchored to the surface of a wide band gap semiconductor. Charge separation takes place at the interface via photo-induced electron injection from the dye into the conduction band of the solid. Carriers are transported in the conduction band of the semiconductor to the charge collector. The present concepts evolved in the context of research on Mesoporous Oxide semiconductor films prepared via a sol-gel process. The use of transition metal complexes having a broad absorption band in conjunction with Oxide films of nanocrstalline morphology permits to harvest a large fraction of sunlight. Nearly quantitative conversion of incident photons into electric current is achieved over a large spectral range extending over the whole visible region. Overall solar (standard AM 1.5) to electric conversion efficiencies over 10% have been reached. There are good prospects to produce these cells at lower cost than conventional devices. The lecture will present the current state of the field. We shall discuss new concepts of the dye-sensitized nanocrystalline solar cell (DYSC) including solid heterojunction variants and analyze the perspectives for the future development of the technology into the next millennium.
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long lived photoinduced charge separation and redox type photochromism on Mesoporous Oxide films sensitized by molecular dyads
Journal of the American Chemical Society, 1999Co-Authors: Pierre Bonhote, Jacques-e. Moser, Robin Humphrybaker, Nicolas Vlachopoulos, Shaik M Zakeeruddin, Lorenz Walder, Michael GrätzelAbstract:The photoinduced charge separation in three different assemblies composed of an electron donor D and a chromophore sensitizer S adsorbed on nanocrystalline TiO2 films (D−S|TiO2) was investigated. In all of the systems, the sensitizer was a ruthenium(II) bis-terpyridine complex anchored to the semiconductor surface by a phosphonate group. In two of the assemblies, the donor was a 4-(N,N-di-p-anisylamino) phenyl group linked to the 4‘ position of the terpyridine, either directly (dyad D1−S) or via a benzyl ether interlocking group (dyad D2−S). In the third system, the sensitizer and the donor (3-(4-(N,N-di-p-anisylamino)phenoxy)-propyl-1-phosphonate) were coadsorbed on the surface ((D3+S)|TiO2). Laser flash photolysis showed that the photoinduced charge separation process follows the sequence D−S*|TiO2 D−S+|(e-)TiO2 D+−S|(e-)TiO2 D−S|TiO2 Resonance Raman spectroscopy indicates that in the excited assemblies D2−S*|TiO2 and (D3+S*)|TiO2, one electron is promoted from the metal center to the terpyridine ligand...
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Mesoporous Oxide junctions and nanostructured solar cells
Current Opinion in Colloid & Interface Science, 1999Co-Authors: Michael GrätzelAbstract:Abstract Mesoporous films of wide-band gap semiconductor Oxides are an important new class of electronic materials. They are constituted by a network of nanocrystalline particles of Oxides, such as titania, niobia or zinc Oxide, sintered together to allow for charge carrier transport to take place. The pores between the nanoparticles are filled with an electrolyte or a solid state organic hole conductor forming an interpenetrating heterojunction of very large contact area. These junctions exhibit extraordinary opto-electronic properties due to their large surface area to volume ratio leading to applications in different domains, such as photovoltaics, intercalation batteries, electrochromic and electroluminescent displays, photocatalysis and chemical sensors. Of particular interest are dye-sensitized heterojunctions, where photo-induced charge separation occurs at the interface between the Mesoporous Oxide and the hole conductor or the electrolyte. Photovoltaic cells based on this concept form a viable alternative to conventional silicon cells. Solar to electric power conversion efficiencies exceeding 10% have been reached with Mesoporous titania films derivatized with molecular charge transfer sensitizers and used in conjunction with organic iodide/triiodide-based redox electrolytes. Long-term accelerated light-soaking tests have shown the system to be intrinsically stable. This article summarized recent developments in this field including a discussion of solid state dye-sensitized heterojunctions employing spirobifluorene-connected arylamines as hole transport materials.
Yadong Yin - One of the best experts on this subject based on the ideXlab platform.
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surface protected etching of Mesoporous Oxide shells for the stabilization of metal nanocatalysts
Advanced Functional Materials, 2010Co-Authors: Qiao Zhang, Ilkeun Lee, Francisco Zaera, Yadong YinAbstract:Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general "encapsulation and etching" strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective Oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface-protected etching process, both yolk-shell and core― satellite type nanoreactors are synthesized and their utilization in liquid- and gas-phase catalysis is demonstrated. The thermal and chemical stability ofthe metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework.
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Surface‐Protected Etching of Mesoporous Oxide Shells for the Stabilization of Metal Nanocatalysts
Advanced Functional Materials, 2010Co-Authors: Qiao Zhang, Ilkeun Lee, Francisco Zaera, Yadong YinAbstract:Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general "encapsulation and etching" strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective Oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface-protected etching process, both yolk-shell and core― satellite type nanoreactors are synthesized and their utilization in liquid- and gas-phase catalysis is demonstrated. The thermal and chemical stability ofthe metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework.
David Grosso - One of the best experts on this subject based on the ideXlab platform.
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Electrochemical approaches for the fabrication and/or characterization of pure and hybrid templated Mesoporous Oxide thin films: a review
Analytical and Bioanalytical Chemistry, 2013Co-Authors: Mathieu Etienne, David Grosso, Yann Guillemin, Alain WalcariusAbstract:Electrochemistry can be used for fabrication and characterization of Mesoporous Oxide films. First, this review provides insight into the methods used to prepare templated Mesoporous thin films on an electrode surface, i.e., evaporation-induced self-assembly (EISA) and electrochemically assisted self-assembly (EASA). Electrochemical characterization of mass transport processes in pure and organically functionalized Mesoporous Oxide films is then discussed. The electrochemical response can be basically restricted by the electron/mass transfer reaction at the electrode-film interface and diffusion through mesopore channels. The contributions of cyclic voltammetry, hydrodynamic voltammetry, electrochemical impedance spectroscopy, and scanning electrochemical microscopy to the characterization of films with distinct mesostructures are finally described, with special emphasis on identification of conditions that can affect the electrochemical response recorded with such modified electrodes.
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Electrochemical approaches for the fabrication and/or characterization of pure and hybrid templated Mesoporous Oxide thin films: a review
Analytical and Bioanalytical Chemistry, 2013Co-Authors: Mathieu Etienne, David Grosso, Yann Guillemin, Alain WalcariusAbstract:Electrochemistry can be used for fabrication and characterization of Mesoporous Oxide films. First, this review provides insight into the methods used to prepare templated Mesoporous thin films on an electrode surface, i.e., evaporation-induced self-assembly (EISA) and electrochemically assisted self-assembly (EASA). Electrochemical characterization of mass transport processes in pure and organically functionalized Mesoporous Oxide films is then discussed. The electrochemical response can be basically restricted by the electron/mass transfer reaction at the electrode–film interface and diffusion through mesopore channels. The contributions of cyclic voltammetry, hydrodynamic voltammetry, electrochemical impedance spectroscopy, and scanning electrochemical microscopy to the characterization of films with distinct mesostructures are finally described, with special emphasis on identification of conditions that can affect the electrochemical response recorded with such modified electrodes. Figure Permeability through Mesoporous thin films
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Sorption Properties of Mesoporous Multilayer Thin Films
Journal of Physical Chemistry C, 2008Co-Authors: María Cecilia Fuertes, David Grosso, Cédric Boissière, Clément Sanchez, Silvia Colodrero, Gabriel Lozano, Agustín R. González-elipe, Galo J. De A. A. Soler-illia, Hernán MíguezAbstract:The vapor sorption properties of multilayers made of ordered Mesoporous thin films with tailored composition and mesostructure are herein investigated. Optical reflectance measurements versus partial pressure of several vapors are performed to analyze the interplay between the affinity to and the accessibility of the different types of layers in the structure. We find that the behavior of a Mesoporous Oxide layer within the multilayer largely differs from that of the isolated thin film, its sorption properties being determined by the interaction with neighboring films. An explanation of the phenomena observed in these complex systems is provided in terms of the pore size, the affinity of each type of layer to specific compounds, and the effect of neighboring layers in the sorption properties of bilayers by an independent environmental ellipsometric study.
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stability of Mesoporous Oxide and mixed metal Oxide materials under biologically relevant conditions
Chemistry of Materials, 2007Co-Authors: John D. Bass, David Grosso, Cédric Boissière, Emmanuel Belamie, Thibaud Coradin, Clément SanchezAbstract:The dynamic behavior of nanoscale Mesoporous Oxide materials exposed to aqueous solutions under biologically relevant conditions is shown to be highly dependent on composition, porosity, and calcination temperature. Dynamic processes were followed as a function of exposure on thin Oxide films amenable to environmental ellipsometry porosimetry for the analysis of mechanical strength and pore size distributions as a function of exposure. Additionally, X-ray photoelectron spectroscopy was used for the elucidation of compositional changes as a function of exposure. Combined, this approach gives the first detailed, quantitative information of the degradation of nanoscale Oxide materials under biologically relevant conditions. This approach also shows the utility of using film geometry as a convenient model system for the study of dynamic properties, as films are amenable to sensitive ellipsometric characterization. Pure silica films underwent a rapid degradation, occurring on the time scale of hours, while sil...
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Stability of Mesoporous Oxide and Mixed Metal Oxide Materials under Biologically Relevant Conditions
Chemistry of Materials, 2007Co-Authors: John D. Bass, David Grosso, Cédric Boissière, Emmanuel Belamie, Thibaud Coradin, Clément SanchezAbstract:The first detailed study of the dynamic behavior of nanoporous Oxide interfaces interacting with biologically relevant environments is presented using environmental ellipsometry porosimetry and XPS. Evolution of the pore structure, mechanical properties, and composition is shown using thin films as model systems. Behavior is highly dependent on composition, porosity, and calcination temperature.
Qiao Zhang - One of the best experts on this subject based on the ideXlab platform.
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surface protected etching of Mesoporous Oxide shells for the stabilization of metal nanocatalysts
Advanced Functional Materials, 2010Co-Authors: Qiao Zhang, Ilkeun Lee, Francisco Zaera, Yadong YinAbstract:Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general "encapsulation and etching" strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective Oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface-protected etching process, both yolk-shell and core― satellite type nanoreactors are synthesized and their utilization in liquid- and gas-phase catalysis is demonstrated. The thermal and chemical stability ofthe metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework.
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Surface‐Protected Etching of Mesoporous Oxide Shells for the Stabilization of Metal Nanocatalysts
Advanced Functional Materials, 2010Co-Authors: Qiao Zhang, Ilkeun Lee, Francisco Zaera, Yadong YinAbstract:Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general "encapsulation and etching" strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective Oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface-protected etching process, both yolk-shell and core― satellite type nanoreactors are synthesized and their utilization in liquid- and gas-phase catalysis is demonstrated. The thermal and chemical stability ofthe metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework.
Galo J. A. A. Soler-illia - One of the best experts on this subject based on the ideXlab platform.
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Metalloporphyrins into Mesoporous Photonic Crystals: Towards Nanostructured Sensing Devices
2019Co-Authors: Rolando M. Caraballo, Galo J. A. A. Soler-illia, Diego Onna, Nicolás López Abdala, Mariana HamerAbstract:<p>Metalloporphyrins are molecules capable of optically sensing targets due to their specific reactivity. Shifts in metalloporphyrins spectra are usually in the order of 30 nm, requiring a spectrophotometer for transducing the analyte concentration. Mesoporous Oxide thin films photonic crystals (PC) act as optical filters, while their pores can host molecular moieties. In this work used a metalloporphyrin, Mn<sup>III</sup> meso-tetra(N-methyl-4-pyridyl) porphyrin (MP), to add a recognition functionality to a PC and, at the same time, retain their pore network, in order to develop a versatile and portable sensing device for volatile amines. The hybrid material MP@PC was prepared by immersion of the PC, synthesized from two Mesoporous Oxides with different refractive index, in an MP solution. The system was characterized by UV-Vis absorption and FTIR spectroscopies, and SEM microscopy. Sensing of small molecules was tested using ethylenediamine (EDA) as a volatile amine model, showing an absorbance increase in the PC spectral window with promising analytical parameters. The hybrid material presents enhanced sensing capabilities compared to MP or PC alone. A prototype device was built, aiming for a future design of simple, low-cost equipment, with a light emitting diode and a light-dependent resistor, including the MP@PC sensor. The device is capable of sensing with only 1.52 μg of MP on a 1 cm<sup>2</sup> glass slide and it is easily prepared and showed a very small detection limit.</p>
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Chemical Stability of Mesoporous Oxide Thin Film Electrodes under Electrochemical Cycling: from Dissolution to Stabilization
Langmuir : the ACS journal of surfaces and colloids, 2019Co-Authors: Sebastián Alberti, Paula Y. Steinberg, Gustavo Giménez, Heinz Amenitsch, Gabriel Ybarra, Omar Azzaroni, Paula C. Angelomé, Galo J. A. A. Soler-illiaAbstract:Mesoporous Oxide thin films (MOTF) present very high surface areas and highly controlled monodisperse pores in the nanometer range. These features spurred their possible applications in separation membranes and permselective electrodes. However, their performance in real applications is limited by their reactivity. Here, we perform a basic study of the stability of MOTF toward dissolution in aqueous media using a variety of characterization techniques. In particular, we focus in their stability behavior under the influence of ionic strength, adsorption of electrochemical probes, and applied electrode potential. Mesoporous silica thin films present a limited chemical stability after electrochemical cycling, particularly under high ionic strength, due to their high specific surface area and the interactions between the electrochemical probes and the surface. In contrast, TiO2 or Si0.9Zr0.1O2 matrices present higher stability; thus, they are an adequate alternative to produce accessible, sensitive, and robus...
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Diffusion of single dye molecules in hydrated TiO2 Mesoporous films.
Physical chemistry chemical physics : PCCP, 2017Co-Authors: Juan Francisco Angiolini, Paula Y. Steinberg, Paula C. Angelomé, Galo J. A. A. Soler-illia, Alejandro Wolosiuk, Martin Stortz, Esteban E. Mocskos, Luciana Bruno, Valeria LeviAbstract:Mesoporous Oxide films are attractive frameworks in technological areas such as catalysis, sensing, environmental protection, and photovoltaics. Herein, we used fluorescence correlation spectroscopy to explore how the pore dimensions of hydrated TiO2 Mesoporous calcined films modulate the molecular diffusion. Rhodamine B molecules in Mesoporous films follow a Fickian process 2–3 orders slower compared to the probe in water. The mobility increases with the pore and neck radii reaching an approximately constant value for a neck radius >2.8 nm. However, the pore size does not control the dye diffusion at low ionic strength emphasizing the relevance of the probe interactions with the pore walls on dye mobility. In conclusion, our results show that the thermal conditioning of TiO2 Mesoporous films provides an exceptional tool for controlling the pore and neck radii on the nanometer scale and has a major impact on molecular diffusion within the Mesoporous network.
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Silver nanoparticle-Mesoporous Oxide nanocomposite thin films: a platform for spatially homogeneous SERS-active substrates with enhanced stability.
ACS applied materials & interfaces, 2014Co-Authors: Alejandro Wolosiuk, Nicolás G. Tognalli, Eduardo D. Martínez, M. Granada, M. Cecilia Fuertes, Horacio E. Troiani, Sara A. Bilmes, Alejandro Fainstein, Galo J. A. A. Soler-illiaAbstract:We introduce a nanoparticle-Mesoporous Oxide thin film composite (NP-MOTF) as low-cost and straightforward sensing platforms for surface-enhanced Raman Spectroscopy (SERS). Titania, zirconia, and silica Mesoporous matrices templated with Pluronics F-127 were synthesized via evaporation-induced self-assembly and loaded with homogeneously dispersed Ag nanoparticles by soft reduction or photoreduction. Both methods give rise to uniform and reproducible Raman signals using 4-mercaptopyridine as a probe molecule. Details on stability and reproducibility of the Raman enhancement are discussed. Extensions in the design of these composite structures were explored including detection of nonthiolated molecules, such as rhodamine 6-G or salicylic acid, patterning techniques for locating the enhancement regions and bilayered Mesoporous structures to provide additional control on the environment, and potential size-selective filtration. These inorganic Oxide–metal composites stand as extremely simple, reproducible, an...
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Controlled deposition of silver nanoparticles in Mesoporous single- or multilayer thin films: from tuned pore filling to selective spatial location of nanometric objects.
Small (Weinheim an der Bergstrasse Germany), 2008Co-Authors: María Cecilia Fuertes, Alejandro Wolosiuk, M. Marchena, María Claudia Marchi, Galo J. A. A. Soler-illiaAbstract:Silver nanoparticle assemblies are embedded within Mesoporous Oxide thin films by an in situ mild reduction leading to nanoparticle-Mesoporous Oxide thin-film composites (NP@MOTF). A quantitative method based on X-ray reflectivity is developed and validated with energy dispersive spectroscopy in order to assess pore filling. The use of dilute formaldehyde solutions leads to control over the formation of silver nanoparticles within Mesoporous titania films. Inclusion of silver nanoparticles in Mesoporous silica requires more drastic conditions. This difference in reactivity can be exploited to selectively synthesize nanoparticles in a predetermined layer of a multilayered Mesoporous stack leading to complex 1D-ordered multilayers with precise spatial location of nanometric objects. The metal Oxide nanocomposites synthesized have potential applications in catalysis, optical devices, surface-enhanced Raman scattering, and metal enhancement fluorescence.