Showing papers on "Stokes shift published in 1980"

Luminescence of porphyrins and metalloporphyrins. Part 1.—Zinc(II), nickel(II) and manganese(II) porphyrins

Abstract: Metal-free and ZnTPP complexes exhibit both fluorescence and low temperature phosphorescence, MnIITPP shows only low temperature phosphorescence while NiIITPP is non-luminescent. The absorption spectra show that there is little interaction between the metal and the porphyrin π-system so that the excited states can be regarded as (ππ*) in nature. Where phosphorescence occurs, the Stokes shift is 3900 ± 100 cm–1 and decreases with increased metal–porphyrin interaction. The rate constants for intersystem crossing and for non-radiative decay from the lowest (ππ*) triplet state depend upon spin–orbital coupling properties. ZnII and NiI exhibit fairly weak spin–orbital coupling but the effectiveness of MnII is enhanced by the paramagnetic character and by favourable geometry. NiIITPP possesses a low energy (dd) excited singlet state which facilitates rapid internal conversion within the singlet manifold.

Thermodynamics of the fluorescent planar concentrator

Abstract: A “generalized brightness theorem” is derived that describes the thermodynamic limitations of the fluorescent planar concentrator. The maximum brightness concentration ratio allowed by thermodynamics is exp (hΔν/kT) where Δν is the Stokes shift in fluorescence.

Photoluminescence from amorphous phosphorus

Abstract: Efficient photoluminescence is observed from bulk red amorphous phosphorus. The photoluminescence properties are similar to those seen in the chalcogenide systems such as As2Se3. The emission occurs as a broad-band centered at 1.33 eV. Fatiguing of the luminescence takes place, as does the concomitant infra-red restoration commonly observed in chalcogenide glasses. The luminescence is found to decrease exponentially with increasing temperature. Measurement of the excitation spectrum suggests a large Stokes shift, and indicates that this material has a band-gap of about 2.1 eV. Comparison with bulk amorphous arsenic suggests that the luminescence processes in these two group V elements are different.

The Origin of the J Band

Abstract: The J band is a very sharp absorption band which has been found in the aggregate of some cyanine dyes. It is characterized by a red shifted unusual sharp absorption band and zero Stokes shift of fluorescence. The condition for the appearance of the J band is investigated in order to find the mechanism of molecular interaction involved in the excited state of dye aggregates. Electronic spectra of single crystals of several dyes are presented and discussed from a view of specific polarization character of the J band. Comparison of spectra of many dyes suggests that strong π electron overlap and large exciton band splitting are important requisite for the appearance of the J band. It implies that the charge resonance state mixes with molecular exciton state when favourable conditions are satisfied, and this will enable fast excitation transfer among molecules in the aggregate.

On the spectra of resonant coherent Raman scattering

Abstract: The spectra of resonant coherent anti-Stokes and Stokes Raman scattering of excited molecules are calculated and discussed. The interaction of light and molecules is treated semi-classically. The energy level diagram of four energy levels describing the process is used in four modifications possible for excited molecules. It is shown that non-vibrational resonances give ‘extra’ maxima in some of the spectra. Comparison of the spectral structure in the Stokes and anti-Stokes components gives information on which of the four schemes the interaction is realized by. The influence of the pumping detuning on the Stokes component shape is pointed out.

Stimulated Raman scattering excited in capillary waveguides by tunable radiation

Abstract: Two-frequency tunable radiation was generated by stimulated Raman scattering in few-mode optical waveguides (benzene-filled quartz capillaries) pumped by a rhodamine 6G laser radiation. The Stokes shift of the Raman band varied when the dye laser radiation was tuned in the range 17 700–17 100 cm−1. This variation was governed by the position of the Raman band relative to the absorption line of benzene in the region of 16 500 cm−1 associated with the sixth harmonic of the C-H valence vibration of benzene.