Raman Spectrum of Er-Y-codoped ZrO2 and Fluorescence Properties of Er3+

Er-Y-codoped ZrO2 mixed oxides with monoclinic, tetragonal and cubic structures were prepared by a sol-gel method. The crystal structure of ZrO2 matrix and the effect of the ZrO2 phases on the fluorescence properties of Er3+ were studied using Raman spectroscopy. The results indicated that the fluorescence properties of Er3+ depend on its local ZrO2 crystal structures. As ZrO2 matrix transferred from monoclinic to tetragonal and cubic phase, the Raman and fluorescence bands of Er3+ decreased in intensities and tended to form a single peak. With 632.8 nm excitation, the bands between 640 and 680 nm were attributed to the fluorescence of Er3+ in the ZrO2 environment. However, only the fluorescence was observed and no Raman spectra were seen under 514.5 nm excitation, while only Raman spectra were observed under 325 nm excitation. UV Raman spectroscopy was found to be more sensitive in the surface region while the information provided by XRD mainly came from the bulk. The phase with lower symmetry forms more easily on the surface than in the bulk.     

新型全色发光材料NaCaPO_4:Dy~(3+)制备及发光性能

釆用高温固相法制备了NaCaPO4∶Dy3+系列样品,并在紫外(UV)及真空紫外(VUV)区域研究了系列样品的发光性能.紫外激发光谱显示在350nm处有最强的激发峰,可以有效地吸收紫外光并将其转化为可见光.真空紫外激发光谱表明,NaCaPO4∶Dy3+能有效地吸收无汞荧光灯的激发源并将其转化为可见光.系列样品发光均呈现为白色,这种材料有潜力作为全色显示材料应用于发光二极管(LED)和无汞荧光灯中.     

Monitoring surface metal oxide catalytic active sites with Raman spectroscopy

The molecular aspect of the Raman vibrational selection rules allows for the molecular structural and reactivity determinations of metal oxide catalytic active sites in all types of oxide catalyst systems (supported metal oxides, zeolites, layered hydroxides, polyoxometalates (POMs), bulk pure metal oxides, bulk mixed oxides and mixed oxide solid solutions). The molecular structural and reactivity determinations of metal oxide catalytic active sites are greatly facilitated by the use of isotopically labeled molecules. The ability of Raman spectroscopy to (1) operate in all phases (liquid, solid, gas and their mixtures), (2) operate over a very wide temperature (-273 to >1000 °C) and pressure (UHV to ?100 atm) range, and (3) provide molecular level information about metal oxides makes Raman spectroscopy the most informative characterization technique for understanding the molecular structure and surface chemistry of the catalytic active sites present in metal oxide heterogeneous catalysts. The recent use of hyphenated Raman spectroscopy instrumentation (e.g., Raman-IR, Raman-UV-vis, Raman-EPR) and the operando Raman spectroscopy methodology (e.g., Raman-MS and Raman-GC) is allowing for the establishment of direct structure-activity/selectivity relationships that will have a significant impact on catalysis science in this decade. Consequently, this critical review will show the growth in the use of Raman spectroscopy in heterogeneous catalysis research, for metal oxides as well as metals, is poised to continue to exponentially grow in the coming years (173 references).     

新型全色发光材料NaCaPO4∶Dy3+制备及发光性能

釆用高温固相法制备了NaCaPO4∶Dy3+系列样品, 并在紫外(UV)及真空紫外(VUV)区域研究了系列样品的发光性能. 紫外激发光谱显示在350 nm处有最强的激发峰, 可以有效地吸收紫外光并将其转化为可见光. 真空紫外激发光谱表明, NaCaPO4∶Dy3+能有效地吸收无汞荧光灯的激发源并将其转化为可见光. 系列样品发光均呈现为白色, 这种材料有潜力作为全色显示材料应用于发光二极管(LED)和无汞荧光灯中.     

A UV resonance Raman (UVRR) spectroscopic study on the extractable compounds of Scots pine (Pinus sylvestris) wood. Part I: lipophilic compounds

The wood resin in Scots pine (Pinus sylvestris) stemwood and branch wood were studied using UV resonance Raman (UVRR) spectroscopy. UVRR spectra of the sapwood and heartwood hexane extracts, solid wood samples and model compounds (six resin acids, three fatty acids, a fatty acid ester, sitosterol and sitosterol acetate) were collected using excitation wavelengths of 229, 244 and 257 nm. In addition, visible Raman spectra of the fatty and resin acids were recorded. Resin compositions of heartwood and sapwood hexane extracts were determined using gas chromatography. Raman signals of both conjugated and isolated double bonds of all the model compounds were resonance enhanced by UV excitation. The oleophilic structures showed strong bands in the region of 1660-1630 cm(-1). Distinct structures were enhanced depending on the excitation wavelength. The UVRR spectra of the hexane extracts showed characteristic bands for resin and fatty acids. It was possible to identify certain resin acids from the spectra. UV Raman spectra collected from the solid wood samples containing wood resin showed a band at approximately 1650 cm(-1) due to unsaturated resin components. The Raman signals from extractives in the resin rich branch wood sample gave even more strongly enhanced signals than the aromatic lignin.     

Design of unique titanium oxide photocatalysts by an advanced metal ion-implantation method and photocatalytic reactions under visible light irradiation

The metal ion-implantation of titanium oxide with various transition metal ions was carried out by applying by high voltage acceleration. The subsequent calcination of the implanted TiO₂ in oxygen at around 723 K resulted in a large shift in the absorption spectra of the TiO₂ toward visible light regions, its extent being dependent on the amount and the kind of metal ions implanted. Such metal ion-implanted titanium oxide catalysts were active in carrying out various photocatalytic reactions such as the decomposition of NO into N₂, O₂ and N₂O at 275 K under irradiation with visible light longer than 450 nm. The application of this advanced, high energy metal ion-implantation method enables the novel design of titanium oxide photocatalysts which can absorb and initiate vital reactions under visible light and will contribute to the development of catalytic systems utilizing solar energy.     

Thermal and plasma synthesis of metal oxide nanoparticles from MOFs with SERS characterization

Aluminum oxide (Al₂O₃) and chromium oxide (Cr₂O₃) nanoparticles were synthesized by thermolysis of metal-organic frameworks (MOFs). Further O₂ plasma treatment is required to obtain high crystalline quality metal oxides. The composition and morphology of metal oxide nanoparticles were confirmed by powder X-ray diffraction and scanning electron microscopy characterization, respectively. The quality of synthesized metal oxides was also examined by observing the surface-enhanced Raman scattering (SERS) spectra of methyl orange adsorbed on Al₂O₃ and Cr₂O₃. The observed SERS effect can be ascribed to charge-transfer (CT) resonance effect between methyl orange and metal oxide surfaces. UV–vis absorption spectra and DFT calculations of metal oxide- methyl orange complexes have confirmed that the observed SRS effect is due to CT resonance between the metal oxide nanoparticles and the adsorbed methyl orange molecules.     

UV and visible Raman studies of oxygen vacancies in rare-earth-doped ceria

Surface properties of rare-earth (RE) doped ceria (RE = Sm, Gd, Pr, and Tb) were investigated by UV (325 nm) and visible (514, 633, and 785 nm) Raman spectroscopy, combined with UV-vis diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectra techniques. It was found that the optical absorption property of samples, the wavelength of detecting laser line, and the inhomogeneous distribution of the dopants significantly affected the obtained surface information, namely, the peak intensity and shape at ca. 460 and 570 cm(-1), as well as the observed oxygen vacancy concentration (A(570)/A(460)). The UV laser line detected the surface information of RE-doped ceria and disclosed the presence of many oxygen vacancies in the samples. The visible laser lines penetrated into the inner layer of the Sm- or Gd-doped CeO(2) and reflected the whole information of samples because of their weak absorptions of the visible laser. However, the Pr- or Tb-doped CeO(2) absorbed visible light strongly; thus, the laser can only determine the outer surface information of the sample.     

UV Raman spectroscopic study on TiO2. I. Phase transformation at the surface and in the bulk

Phase transformation of TiO2 from anatase to rutile is studied by UV Raman spectroscopy excited by 325 and 244 nm lasers, visible Raman spectroscopy excited by 532 nm laser, X-ray diffraction (XRD), and transmission electron microscopy (TEM). UV Raman spectroscopy is found to be more sensitive to the surface region of TiO2 than visible Raman spectroscopy and XRD because TiO2 strongly absorbs UV light. The anatase phase is detected by UV Raman spectroscopy for the sample calcined at higher temperatures than when it is detected by visible Raman spectroscopy and XRD. The inconsistency in the results from the above three techniques suggests that the anatase phase of TiO2 at the surface region can remain at relatively higher calcination temperatures than that in the bulk during the phase transformation. The TEM results show that small particles agglomerate into big particles when the TiO2 sample is calcined at elevated temperatures and the agglomeration of the TiO2 particles is along with the phase transformation from anatase to rutile. It is suggested that the rutile phase starts to form at the interfaces between the anatase particles in the agglomerated TiO2 particles; namely, the anatase phase in the inner region of the agglomerated TiO2 particles turns out to change into the rutile phase more easily than that in the outer surface region of the agglomerated TiO2 particles. When the anatase particles of TiO2 are covered with highly dispersed La2O3, the phase transformation in both the bulk and surface regions is significantly retarded, owing to avoiding direct contact of the anatase particles and occupying the surface defect sites of the anatase particles by La2O3.     

Raman and surface Raman spectroscopy with ultraviolet excitation

We record the accurate and reliable Raman spectra of benzoic acid (BA), p-nitrobenzoic acid (PNBA) and o-nitrobenzoic (ONBA) in aqueous solution with ultraviolet excitation. And we find that the ultraviolet (UV) Raman spectrum of aqueous BA solution has one-to-one correspondence to that of BA solid whereas the others are less resemble to the solid counterparts. We also report surface Raman spectroscopy of them in silver colloid without any enhancement in UV region and call it surface-unenhanced Raman spectroscopy (SUERS) while the surface-enhanced Raman scattering (SERS) effects are perfect in near infrared or visible regions. It demonstrates the SERS effects are strongly dependent on the excitation wavelength. On the basis of the experiments, we discuss the mechanism of SERS excited in different regions.     

Resonance hyper-Raman excitation profiles and two-photon states of a donor-acceptor substituted polyene

Resonance Raman and resonance hyper-Raman spectra and excitation profiles have been measured for a "push-pull" donor-acceptor substituted conjugated polyene bearing a julolidine donor group and a nitrophenyl acceptor group, in acetone at excitation wavelengths from 485 to 356 nm (two-photon wavelengths for the nonlinear spectra). These wavelengths span the strong visible to near-UV linear absorption spectrum, which appears to involve at least three different electronic transitions. The relative intensities of different vibrational bands vary considerably across the excitation spectrum, with the hyper-Raman spectra showing greater variation than the linear Raman. A previously derived theory of resonance hyper-Raman intensities is modified to include contributions from purely vibrational levels of the ground electronic state as intermediate states in the two-photon absorption process. These contributions are found to have only a slight effect on the hyper-Rayleigh intensities and profiles, but they significantly influence some of the hyper-Raman profiles. The absorption spectrum and the Raman, hyper-Rayleigh, and hyper-Raman excitation profiles are quantitatively simulated under the assumption that three excited electronic states contribute to the one- and two-photon absorption in this region. The transition centered near 400 nm is largely localized on the nitrophenyl group, while the transitions near 475 and 355 nm are more delocalized.     

Ultrafast spectroscopic study of the photochemistry and photophysics of arylhalodiazirines: direct observation of carbene and zwitterion formation

Ultrafast photolysis (lambdaex = 270, 350, or 360 nm) of bromophenyl, chlorophenyl, fluorophenyl, and fluoro-para-trifluoromethylphenyl diazirines produces transient species which absorb broadly in the UV and visible regions. Transient decay can be fit to either mono- or biexponential functions (tau1 approximately 0.3-10 ps, tau2 approximately 10-350 ps; dependent on solvent and halogen). Fluoro- and chlorophenylcarbene are formed within the time resolution of the spectrometer (300 fs, 270 nm excitation). Bromophenyl diazirine decay (270 nm excitation) correlates with the growth of bromophenylcarbene. Solvent and substituent effects on the slower decays of the transient absorptions are consistent with assigning the carriers of transient absorption in the visible region to ring-opened zwitterionic species.     

Optical properties of ZnO and ZnO:In nanorods assembled by sol-gel method

Self-assembled zinc oxide (ZnO) and indium-doping zinc oxide (ZnO:In) nanorod thin films were synthesized on quartz substrates without catalyst in aqueous solution by sol-gel method. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), Raman-scattering spectroscopy, room-temperature photoluminescence (PL) spectra, and temperature-dependent PL spectra measurements. XRD and Raman spectra illustrated that there were no single In2O3 phase in ZnO lattice after indium doping. The PL spectra of ZnO showed a strong UV emission band located at 394 nm and a very weak visible emission associated with deep-level defects. Indium incorporation induced the shift of optical band gap, quenching of the near-band-edge photoluminescence and enhanced LO mode multiphonon resonant Raman scattering in ZnO crystals at different temperatures. Abnormal temperature dependence of UV emission integrated intensity of ZnO and ZnO:In samples is observed. The local state emission peak of ZnO:In samples at 3.37 eV is observed in low-temperature PL spectra. The near-band-edge emission peak at room temperature was a mixture of excitons and impurity-related transitions for both of two samples.     

Light-driven decarboxylation of wild-type green fluorescent protein

The response of wild-type GFP to UV and visible light was investigated using steady state absorption, fluorescence, and Raman spectroscopies. As reported previously [van Thor, Nat. Struct. Biol. 2002, 9, 37-41], irradiation of GFP results in decarboxylation of E222. Here it is reported that the rate of the light-driven decarboxylation reaction strongly depends on the excitation wavelength, decreasing in the order 254 nm > 280 nm > 476 nm. The relative efficiencies of decarboxylation are explained in terms of the Kolbe-type mechanism in which the excited state of the chromophore acts as an oxidant by accepting an electron from E222. Specifically, it is proposed that 254 nm excitation populates the S2 (or higher) excited state of the chromophore, whereas 404 and 476 nm excitation populate the S1 excited state of neutral and anionic forms, respectively, and that the relative oxidizing power of the three excited states controls the rate of the decarboxylation reaction. In addition, the role of W57 in the photophysics of GFP has been probed by mutating this residue to phenylalanine. These studies reveal that while W57 does not affect decarboxylation, this residue is involved in resonance energy transfer with the chromophore, thereby partially explaining the green fluorescence observed upon UV irradiation of wild-type GFP. Finally, comparison of Raman spectra obtained from nonilluminated and decarboxylated forms of wild-type GFP has provided further vibrational band assignments for neutral and anionic forms of the chromophore within the protein. In addition, these spectra provide valuable insight into the specific interactions between the protein and the chromophore that control the optical properties of wild-type GFP.     

Different molecular constituents in pheomelanin are responsible for emission, transient absorption and oxygen photoconsumption

Steady-state absorption and emission spectroscopies, oxygen activation and transient spectroscopy on a single sample of synthetic pheomelanin are compared. The absorption, emission and excitation spectra of pheomelanin depend on the molecular weight (MW) of the dissolved pigment constituents. While weakly-depending on MW, the maximum of the emission excitation spectrum is approximately 400 nm. The electron paramagnetic resonance oximetry measurements show a clear increase in oxygen uptake between 338 and 323 nm, and also reveal a local enhancement around approximately 370 nm. Pump-probe absorption spectroscopy reveals that photoexcitation of pheomelanin by UVA light generates a transient absorption peak in the visible and UV regions within the instrument response. The action spectrum for the formation of the 780 nm transient species peaks at approximately 360 nm. While both transient absorption bands show the same ultrafast decay component, the 780 nm peak completely vanishes on the 10s of picosecond time scale, but the UV band shows a kinetic evolution to a subsequent intermediate. While in a similar wavelength range, the maximum of the action spectrum derived from the transient data, the emission excitation spectrum and the action spectrum for photoconsumption all differ from one another, suggesting that the chromophore responsible for each is not that same. This raises concern about comparing the results from different photochemical methodologies for melanin, which is a specific case of comparing data on systems where molecular constituents are not well defined.     

The preparation of thin ordered transition metal oxide films on metal single crystals for surface science studies

In this paper the preparation, characterization and properties of metal oxide overlayers on dissimilar metal substrates is reviewed. It is shown that using a general recipe metal oxide surfaces can be produced, which are easily accessible with modern surface science techniques. Many different stoichiometries and structures of the oxides can be prepared by variation of the preparation conditions, that do or do not have a counterpart in bulk oxide surfaces. In addition information about the metal oxide surfaces is obtained without experimental problems such as sample mounting, sample heating and sample purity.     

Normal Raman and surface enhanced Raman spectroscopic experiments with thin layer chromatography spots of essential amino acids using different laser excitation sources

A comparative study of the feasibility and efficiency of Raman spectroscopic detection of thin layer chromatography (TLC) spots of some weak Raman scatterers (essential amino acids, namely, glycine and L-forms of alanine, serine, valine, proline, hydroxyproline, and phenylalanine) was carried out using four different visible and near-infrared (NIR) laser radiations with wavelengths of 532, 633, 785, and 1064 nm. Three types of commercial TLC plates were tested and the possibility of inducing surface enhanced Raman scattering (SERS) by means of Ag-sol was also investigated. The spectra obtained from spotted analytes adsorbed on TLC plates were of very different quality strongly depending on the excitation wavelength, the wetness of the samples, and the compounds examined. The best results were obtained with the simple silica TLC plate, and it has been established that the longest wavelength (lowest energy) NIR excitation of a Nd:YAG laser is definitely more suitable for generating normal Raman scattering of analyte spots than any of the visible radiations. Concerning SERS with application of Ag-sol to the TLC spots, 1-3 orders of magnitude enhancement was observed with wet samples, the greatest with the 532 nm radiation and gradually smaller with the longer wavelength excitations. It is shown, however, that due to severe adsorption-induced spectral distortions and increased sensitivity to microscopic inhomogeneity of the sample, none of the SERS spectra obtained with the dispersive Raman microscope operating in the visible region were superior to the best NIR normal FT-Raman spectra, as far as sample identification is concerned.     

Formation of mixed d- and f-block metal clusters in inert matrices: comparison of the observed and theoretical optical spectra of AgHo

The UV visible spectra obtained after simultaneous cocondensation of silver and holmium atoms with argon matrices at 9 K have been studied in the 200-800 nm region. While no new feature can be observed upon deposition, selective irradiation into both silver or holmium atomic absorptions results in growth of a new band at 430 nm, associated with formation of a mixed silver holmium species, tentatively assigned as AgHo. To support the assignment of the observed bands ab initio quantum chemical calculations were carried out for the dinuclear and trinuclear silver and holmium species, using pseudopotential approaches. Results for the electronic excitation energies and corresponding transition dipole moments for the diatomic molecules Ag2, Ho2, AgHo provide evidence that the 430 nm band should be attributed to the mixed cluster AgHo (theoretical band position at 436 nm), while the doublets at 498/504 and 558/563 nm belong to the homonuclear species Ho2 (theoretical values are at 482 and 562 nm). First conclusions are drawn with respect to the formation of the metal trimers Ho3, Ag2Ho, AgHo2.     

On the structure of vanadium oxide supported on aluminas: UV and visible raman spectroscopy, UV-visible diffuse reflectance spectroscopy, and temperature-programmed reduction studies

Vanadia species on aluminas (delta- and gamma-Al2O3) with surface VOx density in the range 0.01-14.2 V/nm2 have been characterized by UV and visible Raman spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), and temperature-programmed reduction in hydrogen. It is shown that the alumina phase has little influence on the structure and reducibility of surface VOx species under either dehydrated or hydrated conditions. Three similar types of dispersed VOx species, i.e., monovanadates, polyvanadates, and V2O5, are identified on both aluminas under dehydrated conditions. Upon hydration, polymerized VOx species dominate on the surfaces of the two aluminas. The broad Raman band at around 910 cm(-1), observed on dehydrated V/delta-, gamma-Al2O3 at all V loadings (0.01-14.2 V/nm2), is assigned to the interface mode (V-O-Al) instead of the conventionally assigned V-O-V bond. The direct observation of the interface bond is of significance for the understanding of redox catalysis because this bond has been considered to be the key site in oxidation reactions catalyzed by supported vanadia. Two types of frequency shifts of the V=O stretching band (1013-1035 cm(-1)) have been observed in the Raman spectra of V/Al2O3: a shift as a function of surface VOx density and a shift as a function of excitation wavelength. The shift of the V=O band to higher wavenumbers with increasing surface VOx density is due to the change of VOx structure. The V=O stretching band in dispersed vanadia always appears at lower wavenumber in UV Raman spectra than in visible Raman spectra for the same V/Al2O3 sample. This shift is explained by selective resonance enhancement according to the UV-Vis DRS results. It implies that UV Raman has higher sensitivity to isolated and less polymerized VOx species while visible Raman is more sensitive to highly polymerized VOx species and crystalline V2O5. These results show that a multiwavelength excitation approach provides a more complete structural characterization of supported VOx catalysts.     

Library of FT-Raman spectra of pigments, minerals, pigment media and varnishes, and supplement to existing library of Raman spectra of pigments with visible excitation.

Sixty pigments, minerals and media have been analysed by Fourier-transform Raman (FT-Raman) microscopy in order to assemble a database of reference FT-Raman spectra for scientists working at the Arts-Science interface. An earlier library of Raman spectra compiled using visible excitation has been extended by the addition of 22 further reference spectra obtained with 780.0, 647.1, 632.8 and/or 514.5 nm excitation. The relative merits of 1064 nm and visible excitation are discussed.