UV and vacuum UV excited luminescence of naphthoyl cellulose

The absorbance, fluorescence and phosphorescence spectra of cellulose containing chemically substituted naphthoyl chromophores, substituted in different morphological positions in the cellulose structure, have been investigated. Tentative interpretations of the spectra have been put forward. Of particular interest is the vacuum ultra-violet fluorescence, which demonstrates that excitation energy transfer from the cellulose matrix to the naphthoyl chromophore, postulated previously to be the mechanism for the protective action afforded by dye and aromatic substitutents against photo- and γ-irradiation, is not significant in this spectral region.     

White luminescence of Tm-Dy ions co-doped aluminoborosilicate glasses under UV light excitation

Tm³⁺ and Dy³⁺ ions co-doped aluminoborosilicate glasses were prepared in this study. The luminescence properties of the glasses were analyzed. A combination of blue, green, yellow, and red emission bands was shown for these glasses, and white light emission could be observed under UV light excitation. White light luminescence color could be changed by varying the excitation wavelength. Concentration quenching effect was investigated in this paper. Furthermore, the dependence of luminescence properties on glass compositions was studied. Results showed that the luminescence intensity changed with different network modifier oxides, while the white color luminescence was not affected significantly.     

Two-photon excited fluorescence detection at 420 nm for label-free detection of small aromatics and proteins in microchip electrophoresis

Two photon excited (TPE) fluorescence detection was applied to native fluorescence detection of aromatics in microchip electrophoresis (MCE). This technique was evaluated as an alternative to common one photon excitation in the deep UV spectral range. TPE enables fluorescence detection of unlabeled aromatic compounds, even in non-deep UV-transparent microfluidic chips. In this study, we demonstrate the proof of concept of native TPE fluorescence detection of small aromatics in commercial microfluidic glass chips. Label-free TPE fluorescence detection of native proteins and small aromatics in MCE was achieved within the micromolar concentration range, utilising 420 nm excitation light.     

Biomodulative effects induced by 805 nm laser light irradiation of normal and tumor cells

The influence of light emitted from a diode laser centred at λ = 805 nm was investigated on murine skeletal myotubes (C2), normal urothelial cells (HCV29), human squamous carcinoma cells of the gingival muscosa (ZMK) and urothelial carcinoma cells (J82) in a computer-controlled irradiation chamber. Cells were treated with varying fluences between 0 and 20 J cm⁻². The response was tested by analysis of the mitotic index using single cell counting after Orcein staining and proliferation index based on BrdU incorporation during DNA synthesis. While the mitotic index of C2, HCV29 and J82 cells increased at a fluence of 4 J cm⁻², irradiation with fluences of 20 J cm⁻² resulted in a slight decrease. ZMK tumor cells showed a decrease of the mitotic index with both fluences. No significant differences could be determined when using irradiances between 10 mW cm⁻² and 150 mW cm⁻². The BrdU test after irradiation showed no significant effects compared to the controls in each cell line.     

Long-term effects of UV light on contractility of rat arteries in vivo

Several studies have shown that UV irradiation may be effective for preventing vascular restenosis or vasopasm. However, the long-term effects of UV light on the physiological properties of vessels such as arterial tension have not been elucidated. We therefore studied the long-term effects of UV using rat carotid arteries treated with UV-B light (wavelength = 313 nm, total energy = 14 mJ/mm2). The animals were sacrificed at 1, 7 and 14 days after UV light exposure, and the carotid arteries were studied by light microscopy and the contractile responses of isolated arterial rings were recorded under isometric tension. UV treatment had induced a substantial loss of smooth muscle cells (SMC) along the entire circumference of the media on days 7 and 14, whereas loss of SMC on day 1 was negligible. Contractile responses of arteries that had been exposed to UV light were significantly reduced on days, 1, 7 and 14. The susceptibility of UV-treated arteries to phenylephrine and prostaglandin F2 alpha was significantly decreased on days 1 and 7, but decreased susceptibility was not seen on day 14. Acetylcholine-induced relaxations were not altered by UV treatment. These results suggest that the long-term effect of UV light is an attenuation of smooth muscle contractility without impairment of endothelial function.     

Transient absorption of vibrationally excited ice Ih

The ultrafast dynamics of HDO:D2O ice Ih at 180 K is studied by midinfrared ultrafast pump-probe spectroscopy. The vibrational relaxation of HDO:D2O ice is observed to proceed via an intermediate state, which has a blueshifted absorption spectrum. Polarization resolved measurements reveal that the intermediate state is part of the intramolecular relaxation pathway of the HDO molecule. In addition, slow dynamics on a time scale of the order of 10-100 ps is observed, related to thermally induced collective reorganizations of the ice lattice. The transient absorption line shape is analyzed within a Lippincott-Schroeder model for the OH-stretch potential. This analysis identifies the main mechanism behind the strong spectral broadening of the v(OH)=1-->2 transition.     

Electrolyte screening effect on the photoprotolytic cycle of excited photoacid in ice

Time-resolved emission was used to measure the photoprotolytic cycle of an excited photoacid as a function of temperature, both in liquid water and in ice, in the presence of an inert salt. The inert salt affects the geminate recombination between the transferred proton with the conjugate base of the photoacid. We used the Debye-Hückel theory to express the screening of the Coulomb electrical potential by the inert salt. We find that in the liquid phase the measured screening effect is small and the Debye-Hückel expression slightly overestimates the experimental effect. In ice, the screening effect is rather large and the Debye-Hückel expression under estimates the measured effect. We explain the large screening in ice by the "salting-out" effect in ice that tends to concentrate the impurities to confined volumes to minimize the ice crystal energy.     

Alternative determination of equivalent dose by green light emitting diodes optically stimulated luminescence using the unstable luminescence

A new method for the determination of the equivalent dose (ED) in minerals has been developed, based on the unstable part of luminescence which fades away at ambient temperatures. Optical stimulated luminescence employing green light emitting diodes is used in two cases; a reference quartz sample and an archaeological ceramic. In both instances the obtained (ED) with the new technique provides a satisfactory agreement within the expected errors.     

Effect of UV light scattering during photopolymerization on UV spectroscopy measurements

A photopolymerization reaction involving 2-hydroxyethylmethacrylate (HEMA), a hydroxytelechelic polybutadiene (HTPB) and 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as photoinitiator has been investigated by Real Time UV and Real Time IR spectroscopies. For this system, RTUV analyses are completely opposite to the expected curves, namely a decrease in the sample absorbance (photobleaching phenomenon). This apparent contradiction has been explained by a scattering phenomenon inside the sample, which can be linked to the formation of sub-structures that can create local fluctuations of refractive index during the polymerization. A four-flux theory, which takes into account the polymer absorption and scattering properties, has allowed us to describe the UV light intensity variation inside the sample.     

Carbodiimide production from cyanamide by UV irradiation and thermal reaction on amorphous water ice

Cyanamide (NH(2)CN), an interstellar molecule, is a relevant molecule in prebiotic chemistry, because it can be converted into urea in liquid water. Carbodiimide (HNCNH), the most stable cyanamide isomer, is able to assemble amino acids into peptides. In this work, using FTIR spectroscopy, we show that carbodiimide can be formed from cyanamide at low temperature (10 K), by a photochemical process in argon matrix, in water matrix, or in solid film. We also report experimental evidence about the carbodiimide formation when cyanamide is condensed at low temperature (50-140 K) on an amorphous water ice surface, or when it is trapped in the water ice. The water ice acts as a catalyst. This isomerization reaction occurs at low temperature (T < 100 K), which agrees with those expected in the interstellar clouds composed of dust grains in which water is the most predominant compound. Finally, the hydrolysis reaction of cyanamide or carbodiimide leading to urea or isourea formation is not observed under our experimental conditions.     

Temperature dependence of excited state proton transfer in ice

We have studied the excited-state proton-transfer rate of four photoacids in ice as a function of temperature. For all four photoacids, we have found a non Arrhenius behavior of the proton-transfer rate constant, k(PT). d(ln k(PT))/d(1/T) decreases as the temperature decreases. The average slope of ln(k(PT))versus 1/T depends on the photoacid strength (pK*). The stronger the photoacid is, the smaller the slope. For the strongest photoacid 2-naphthol-6,8-disulfonate (2N68DS) the largest slope is 35 kJ/mol at about 270 K, and the smallest measured slope is about 8 kJ/mol at about 215 K. We propose that the temperature dependence of k(PT) in ice at the temperature range 270 > T > 200 K can be explained as arising from contributions of two proton-transfer mechanisms over the barrier and tunneling under the barrier. At very low temperatures T < 200 K, the slope of ln(k(PT)) versus 1/T increases again. At about 170 K, the proton-transfer rate is much slower than the radiative rate, and the deprotonated form of the photoacid cannot be detected in the steady-state emission spectrum. At lower temperatures, T < 200 K, the rate further decreases because of a limitation on the reaction caused by the restrictions on the H2O hydrogen reorientations.     

The effect of crystal fragmentation on the luminescence from pulse-irradiated H2O ice

The extent of crystal fragmentation in electron pulse-irradiated H₂O ice does not affect the spectral distribution of the luminescence emitted by the ice, except in the case of the Balmer α-emission at 656 nm, which is reduced in intensity when the extent of ice fragmentation is increased. The luminescence intensity at 400 nm is sufficiently high for luminescence decay half-lives to be measured and these do not change with ice fragmentation. The effect of fragmentation on the Balmer α-intensity is explained by the trapping at dislocations of either exciton or electron precursors to the luminescence.     

The nature of molecular excited states produced by weak light sources

It is shown that upon excitation of a molecule by light from a thermal source, the incident field tends to act as a projection operator for a subspace spanned by eigenstates of the molecular hamiltonian. Furthermore, for chaotic light sources there is an effective upper limit, τ, for the time during which there is coherent excitation. If τ is much greater than the uncertainty minimum, as is normally the case, the reduced density operator for the excited states of the molecule becomes “filtered”, the extent of which determines the pattern of subsequent radiative and radiationless decay processes. The limitation of the “filtering” process to the interval τ provides a new distinction for large- and small-molecule behavior.     

Influence of polarization and wavelength on two-photon excited luminescence of single gold nanospheres

The Brownian rotation of a nearly spherical gold particle capped with ligands can be observed in the correlation profile of the intensity of the two-photon excited luminescence. Here we report on a multi-parameter study of the luminescence properties, including spectral and polarization analysis of the signal at the single particle level. First, the data confirm the role of the radiative de-excitation of the surface plasmons in the luminescence process. Secondly, the results obtained at low power indicate that the capped particle in water can be approximatively described as a spherical rotor acting in the far-field as a point-like absorption and emission dipole of fixed directions. In addition, we show that the dynamics of the ligands, induced by the heat transfer from the particle to its environment, can be partly controlled by the choice of excitation wavelength.     

Real time study of hybrid sol-gel photopolymerization by UV light

Polycrystalline La_0.67 (Sr_1-x Cd _x )_0.33MnO₃ (LSCMO x = 0, 1/8, 2/8, 3/8, 4/8) films were fabricated on Si(100) single crystal substrates by the sol–gel and the rapid annealing process. According to the field-emission scan electron microscopy (FE-SEM) observation and X-ray (XRD) diffraction studies, all the samples are single phase. We also prepared a series of samples by fixing the ratio of La at 0.67. It is shown that with increase of the doping amount x in La_0.67(Sr_1-x Cd _x )_0.33MnO₃, the average A-site cation radius 〈A〉 decreases, the temperature of metal-insulator transition (T_MI) decreases monotonically, ρ and magnetoresistance (MR) values increase dramatically, which can be explained by the lattice effects. The enhanced MR effect at low temperature for the LSCMO film is attributed to the suppression of the spin dependent scattering of polarized electrons at the grain boundaries. The low-field magnetoresistance values under 0.3 T are observed to be 2.48% (x = 0) at 300 K and 37.5% (x = 4/8) at 85 K, respectively.     

The dependence of DNA luminescence on excitation wavelength in the UV/VUV region

Luminescence emission and excitation spectra have been obtained for DNA films at 77 K under vacuum ultraviolet excitation (150–280 nm). The emission spectra, which cover the wavelength range 310 to 490 nm, consists of two components, a short-lived component around 350 nm which is attributed to fluorescence and a longer-lived component around 410 nm believed to be phosphorescence. The excitation spectra, as functions of emission wavelength, are similar in profile with a fairly broad peak around 9240–260 nm) with a shoulder around 200 nm followed by a gradual but constant decrease into the vacuum ultraviolet region of the spectrum. No evidence of autoionization was seen in the region investigated.     

Luminescent europium nanoparticles with a wide excitation range from UV to visible light for biolabeling and time-gated luminescence bioimaging

Silica-encapsulated highly luminescent europium nanoparticles with a wide excitation range from UV to visible light (200-450 nm) have been prepared and used for streptavidin labeling and time-gated luminescence imaging of an environmental pathogen, Giardia lamblia.