Excimer

About: Excimer is a research topic. Over the lifetime, 3725 publications have been published within this topic receiving 75104 citations.

High-Repetition-Rate Excimer-Based UV Laser Excitation Source Avoids Saturation in Resonance Raman Measurements of Tyrosinate and Pyrene

Abstract: UV resonance Raman excitation using low-duty-cycle pulsed lasers such as the Nd:YAG can result in photophysical processes that interfere with Raman spectral studies of ground-state species due to the high incident laser energy fluxes. Depletion of the ground state occurs due to optical absorption and due to the population of intermediate levels which have lifetimes comparable to or longer than the excitation pulse width. In addition, formation of photochemical intermediates can occur. For example, excitation in resonance with the tyrosinate La electronic transition (∼240 nm) results in formation of tyrosyl radicals which deplete the concentration of ground-state tyrosinate molecules; as a result, decreased resonance Raman intensities are observed for vibrational modes of ground-state tyrosinate. For pyrene, excitation in resonance with the S4 electronic transition results in population of the long-lived S1 state via rapid internal conversion. This long-lived state bottlenecks relaxation back to the ground state, thus causing saturation of the ground-state pyrene Raman intensities. Given similar incident average laser powers and focusing conditions, higher-duty-cycle lasers result in decreased saturation. A comparison between a 20-Hz Nd:YAG and a 200-Hz excimer laser-based UV Raman excitation source demonstrates superiority of the excimer in avoiding both Raman saturation and interferences from photochemical transients. For the identical energy flux per pulse, the accompanying tenfold increase in average energy flux for the excimer, over the YAG, results in a dramatic improvement in the spectral signal-to-noise ratios. We report the first measurement of the absolute resonance Raman cross section of pyrene within the S4 transition. The Raman cross section of 48 barns/str measured for the 1632-cm−1 vibration with 240-nm excitation is the largest observed to date.

Excimer fluorescence - XI. Solvent-solute energy transfer

Abstract: The rate parameters of solvent-solute energy transfer and of oxygen-solvent quenching have been determined for solutions of 2, 5-diphenyloxazole in benzene, toluene, p -xylene and mesitylene. The role of excited molecules and excimers in transfer to the solute molecules is considered in terms of the Voltz relations, which include the Forster critical transfer distance, the molecular diffusion coefficients, and the solvent excitation migration coefficient. It is proposed that the migration is due to excimer formation and dissociation, and that the energy transfer occurs by a diffusion/migration-controlled collisional process. Dilution of the solvent decreases the migration, but increases the transfer distance, so that the transfer efficiency remains practically constant. The excimer formation and dissociation rate parameters in the pure alkyl benzenes are evaluated.

PET surface modifications by treatment with monochromatic excimer UV lamps

Abstract: Physical and chemical surface modifications of polyethyleneterephthalate (PET) films due to treatment with excimer UV lamps (222 nm) have been studied. Interpretations of the reactions and products were made in comparison to known PET irradiations with excimer UV lasers and broad-band UV sources. In this context the advantages of the excimer UV lamps as a light source, i.e., a quasi monochromatic radiation source with a power density which is sufficient for initiating surface reactions without changing the topography of the substrate, have been shown. Analytical data on treated PET to characterize the surface modifications were obtained by contact-angle measurements, dyeing with cationic dyestuff, scanning electron microscopy (SEM), photoacoustic Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) studies. With regard to possible industrial applications, the relevance for textile finishing and some perspectives for future developments are pointed out.

Global modeling of a dielectric barrier discharge in Ne-Xe mixtures for an alternating current plasma display panel

Abstract: A global model of a dielectric barrier discharge in Ne–Xe mixtures for an alternating current plasma display panel was developed. This model was used to evaluate electron temperature, plasma density, densities of excited state atoms, wall charge density, current density, excimer density, and vacuum ultraviolet (VUV) intensity, and their gas composition-pressure dependencies, in order to analyze the mechanism of VUV radiation and discharge efficiency. The results show that the intensity ratio of 173 to 147 nm VUV is about a few percent. This means that the contribution of excimers is small in terms of VUV radiation. The maximum discharge efficiency was about 9% for Xe fraction in the range of 2%–12% and gas pressure in the range of 100–600 Torr. Discharge efficiency increases in the high Xe fraction and gas pressure region. The increase of the discharge efficiency is attributed to a decrease of discharge current and an increase of Xer*(3P1) excited state atom, due to the low electron temperature in the hig...