Absorption excitation

Kummer S, Kulzer F, Kettner R, Basche T, Tietz C, Glowatz C and Kryschi C 1997 Absorption, excitation, and... 

Fig. 1. Schematic energy-level diagram for a dye molecule. Electronic states Sq = ground singlet state = first excited singlet state S2 = second excited singlet state Tj = first excited triplet state T2 = second excited triplet state EVS = excited vibrational states. Transitions A = absorption excited states ...

Fluorescent and phosphorescent substances are excited into an unstable energy state by UV light. When they return to the ground state they release a part of the energy taken up in the form of radiation. The emitted radiation is less energetic than the light absorbed and usually lies in the visible part of the spectrum. Since absorption (excitation) and emission obey a linear relationship over a certain range a reduction in absorption leads to a reduction in the luminescence, too. 

A qualitatively different approach to probing multiple pathways is to interrogate the reaction intermediates directly, while they are following different pathways on the PES, using femtosecond time-resolved pump-probe spectroscopy [19]. In this case, the pump laser initiates the reaction, while the probe laser measures absorption, excites fluorescence, induces ionization, or creates some other observable that selectively probes each reaction pathway. For example, the ion states produced upon photoionization of a neutral species depend on the Franck-Condon overlap between the nuclear configuration of the neutral and the various ion states available. Photoelectron spectroscopy is a sensitive probe of the structural differences between neutrals and cations. If the structure and energetics of the ion states are well determined and sufficiently diverse in... 

Figure 5.7 Room-temperature electronic absorption, excitation and emission spectra for 2 in aqueous solution. The excitation spectrum of 2 was recorded by monitoring emission at 400 nm. Reproduced with permission from [31]. Copyright (2004) Royal Society of Chemistry.

Phillips and Schug (24) have suggested that the 390 nm emission, observed when PET is excited with high energy electrons, might be from a triplet state or an excimer. Since the triplet states of both PET and DMT are lower in energy (MSO nm), it is unlikely that the emission is from a triplet state. In addition, excimer formation and emission should not effect the absorption-excitation processes therefore, it is unlikely that the 390 nm emission is from an excimer. 

Spectacular differences in absorption/excitation spectra are often observed for the dyes that exist in protonation-deprotonation equilibria. Their straightforward application is for pH sensing and also for designing the reporters, in which the shifting of such equilibrium by external proton donor or acceptor group is involved in sensing event. 

The incident monochromatic photon-to-current conversion efficiency (IPCE), also called external quantum efficiency, is defined as the number of electrons generated by light in the external circuit divided by the number of incident photons as a function of excitation wavelength. It is expressed in Equation (7).29 In most cases, the photoaction spectrum overlaps with the absorption spectrum of the sensitizer adsorbed on the semiconductor surface. A high IPCE is a prerequisite for high-power photovoltaic applications, which depends on the sensitizer photon absorption, excited state electron injection, and electron transport to the terminals ... 

The reciprocal of the FRET-unperturbed donor lifetime, td, is given by the sum of all rate constants for deactivation. These parameters have been extensively discussed in earlier chapters. We note in passing that the constants with extreme values in Eq. (12.1) disappear if one expresses the absorption (excitation) spectrum of the acceptor in terms of the molecular absorption cross-section, o (2) = 1017ln[10] Njy x e (2)(nnr/moleculc). 

More fluorescence features than just the emission intensity can be used to develop luminescent optosensors with enhanced selectivity and longer operational lifetime. The wavelength dependence of the luminescence (emission spectmm) and of the luminophore absorption (excitation spectrum) is a source of specificity. For instance, the excitation-emission matrix has shown to be a powerful tool to analyze complex mixtures of fluorescent species and fiber-optic devices for in-situ measurements (e.g. 

Representative absorption (excitation) and emission spectra of a fluoro-chrome are provided in Fig. 1. Some degree of overlap between the two spectra is typical, and often the excitation and emission spectra are mirror images of each other. The separation between the wavelengths at which excitation and emission maxima occur is referred to as the Stokes shift. 

The ADF has been measured in deoxygenated solutions with continuous excitation of either argon, krypton or helium-neon lasers. The exciting wavelengths corresponded to the bands of Sq > 1 metalloporphyrin absorption (excitation wavelengths Xex = 514.5 530.9 568.2 nm for ZnTPP and Xex = 568.2 632.8 nm for ZnTBP and CdTBP). 

The fluorescent dye hydroxypyrenetrisulfonic acid (3.27), described in section 3.5.1.6, is used in medical monitoring devices for the pH of blood. Absorption (excitation) bands occur at 405 nm (acid form) and 475 nm (basic form) with emission (fluorescence) at 520 nm. 

Various kinds of visible and ultraviolet spectroscopy—absorption, excitation, emission—are well suited for monitoring certain reaction intermediates. These techniques are complementary to X-ray in that they provide excellent sensitivity and time resolution but low structural precision. 

Cu Y. The absorption, excitation, and emission spectra of the Cu Y specimen were reported earlier (4, 10). The emission line is a perfect Gaussian centered at 18400 cm-- - (543 nm) of... 

The importance of the JT effect in the spectroscopy of s2 ions can be easily observed from the splitting of the 1S0->3f,1, 1P1 absorption (excitation) transitions [6]. Figure 7 gives as an example the spectra of Sb3 + (5s2) in Cs2NaScCl6 at 4.2 and 300 K. The SbClg" octahedron is cubic. The 1S0-3P1 transition at about 30000 cm -1 splits into two components, the 1S0-1/>1 transition at about 40000 cm-1 into three components [24]. This, together with their temperature dependence, is proof of the dynamic JT effect in the 3P state. 

Fig. 12. Franck-Condon energies of the lowest excited states of the complexes as observed in the absorption/excitation spectra of crystalline samples. The broken lines characterize states of which the assignment or the exact energy have not been confirmed by other experiments yet...

Relaxation of the neutral excited complex towards the ground state with emission of fluorescence (process IV). The red shift in the absorption (excitation) spectra of the AH-B complex with respect to the absorption of the bare AH molecule will only measure the increase of the binding energy in the excited neutral form AH - B of the cluster. Then, the emission spectrum will be similar to the fluorescence of the free molecule. 

New advances in PDT include (1) metronomic PDT, in which the photosensitizer and light are delivered at a very low dose rate over extended periods (2) two-photon PDT, with activation being realized either through simultaneous absorption of two low-energy photons (near infrared) or by a sequential absorption (excitation... 

Absorption, Excitation, and Emission Bands of the Alkaline-Earth Oxide Powders... 

Cr-HMS exhibits PL bands at --550-570 ran, upon excitation of the absorption (excitation) bands at 250, 360, and 480 nm. These PL and absorption bands are similar to those obtained earlier with well-defined, highly dispersed chromium oxides grafted onto PVG or silica (Anpo et al., 1982). They can be assigned to CT processes in tetrahedral oxide moieties involving electron transfer from O2 to Cr6+ and the reverse radiative decay, respectively. 

Figure 2-2. HF and CIS predictions of the photoconduction (fundamental gap), photoemission (ionization), and optical absorption (excitation) energies of polyethylene [50, 55]...

Fig. 3.16 Modified Jablonski diagram visualizing radiative, non-radiative and photoproduct forming processes (adopted from Braun et al., 1991 and Pfoertner, 1998). The lifetimes of the individual processes are given in parentheses. 1, Absorption (excitation) So->82 and 2, absorption Sq->S, (10 s) 3, fluorescence S, ->So + hVf (10 -10 s) 4, phosphorescence T, ->So -H hvph (10 -10 s) 1C internal conversion S2->S] + heat (10" -10" s) and...

The state of spin alignment in the lowest triplet state can be prepared (47) by a number of other methods in addition to its preparation by singlet-singlet absorption, e.g., by ground-state singlet+excited triplet-state absorption, excitation by electron scattering, and... 

Chlorophyll is at the very heart of the primary events of photosynthesis. It helps convert the sun s radiant energy into chemical free energy that can be stored in various ways. In this section we will represent light absorption, excitation transfer, and the photochemical step as chemical reactions this will serve as a prelude to a further consideration of certain molecular details of photosynthesis. 

This section discusses applications of IR and Raman spectroscopy to materials with reasonable or even very high conductivity. These systems generally present special problems in addition to those described in earlier sections. Incident radiation interacts not only with the vibrational excitations of the material but also with the free carriers and with its electronic structure. These interactions may create phenomena such as free carrier absorption, excitation across the energy gap, exciton transitions, or light scattering by free electrons. Excitations are very often in the IR spectral range, particularly in the... 

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