Broadening radiative

In addition to the photoluminescence red shifts, broadening of photoluminescence spectra and decrease in the photoluminescence quantum efficiency are reported with increasing temperature. The spectral broadening is due to scattering by coupling of excitons with acoustic and LO phonons [22]. The decrease in the photoluminescence quantum efficiency is due to non-radiative relaxation from the thermally activated state. The Stark effect also produces photoluminescence spectral shifts in CdSe quantum dots [23]. Large red shifts up to 75 meV are reported in the photoluminescence spectra of CdSe quantum dots under an applied electric field of 350 kVcm . Here, the applied electric field decreases or cancels a component in the excited state dipole that is parallel to the applied field the excited state dipole is contributed by the charge carriers present on the surface of the quantum dots. 

Section 3.5.1 described the various effects observed upon excitation at the red-edge of the absorption spectrum. In particular, a lack of energy transfer was first observed by G. Weber (1960) (and is called Weber s effect for this reason). This effect can be explained in terms of inhomogeneous broadening of spectra. In a rigid polar solution of fluorophores that are close enough to undergo non-radiative en-... 

The decrease in temperature predicted by the analysis is relatively small and has not been observed experimentally. Experiments with higher precision and accuracy are warranted for checking if this is an artifact of the present chemistry that does not include the effects of higher hydrocarbon formation and radiative heat loss. The peak temperature was found to decrease because of a decrease in the peak volumetric heat release rate caused by a broadening of the reaction zone. 

Feshbach or compound resonances. These latter systems are bound rotovibra-tional supramolecular states that are coupled to the dissociation continuum in some way so that they have a finite lifetime these states will dissociate on their own, even in the absence of third-body collisions, unless they undergo a radiative transition first into some other pair state. The free-to-free state transitions are associated with broad profiles, which may often be approximated quite closely by certain model line profiles, Section 5.2, p. 270 If bound states are involved, the resulting spectra show more or less striking structures pressure broadened rotovibrational bands of bound-to-bound transitions, e.g., the sharp lines shown in Fig. 3.41 on p. 120, and more or less diffuse structures arising from bound-to-free and free-to-bound transitions which are also noticeable in that figure and in Figs. 6.5 and 6.19. At low spectroscopic resolution or at high pressures, these structures flatten, often to the point of disappearance. Spectral contributions of bound dimer states show absorption dips at the various monomer Raman lines, as in Fig. 6.5. 

Given normal energy separations between electronic states, of up to ca. 104 cm-1, the transitions to the higher excited states display broader bands than those to the first excited state. The increased broadening is not accountable for in terms of radiative effects. 

To conclude this discussion we have summarized in Table II the general features of inhomogeneous broadening and radiative decay of large molecules. 

Fig. 6.17 Tunnelling and saddle point ionization in Li. (a) Experimental map of the energy levels of Li m = 1 states in a static field. The horizontal peaks arise from ions collected after laser excitation. Energy is measured relative to the one-electron ionization limit. Disappearance of a level with increasing field indicates that the ionization rates exceed 3 x 105 s 1. The dotted line is the classical ionization limit given by Eqs. (6.35) and (6.36). One state has been emphasized by shading, (b) Energy levels for H (n = 18-20, m = 1) according to fourth order perturbation theory. Levels from nearby terms are omitted for clarity. Symbols used to denote the ionization rate are defined in the key. The tick mark indicates the field where the ionization rate equals the spontaneous radiative rate, (c) Experimental map as in (a) except that the collection method is sensitive only to states whose ionization rate exceeds 3 x 105 s-1. At high fields, the levels broaden into the continuum in agreement with tunnelling theory for H (from ref. 32).

These features of lines of various spectra (X-ray, emission, photoelectron, Auger) are determined by the same reason, therefore they are discussed together. Let us briefly consider various factors of line broadening, as well as the dependence of natural line width and fluorescence yield, characterizing the relative role of radiative and Auger decay of a state with vacancy, on nuclear charge, and on one- and many-electron quantum numbers. 

The most time consuming parts of the forward model are the calculation of the absorption coefficients and the calculation of the radiative transfer. A spectral resolution of Av = 0.0005 cm 1 is considered necessary in order to resolve the shape of Doppler-broadened lines. To avoid repeated line-shape and radiative transfer calculations at this high resolution, two optimizations have been implemented ... 

Natural broadening, due to the finite lifetime of the radiative- state of the emitting atom ... 

Fast non-radiative relaxation of excited states leads to broadening of the spectral lines. The amount of broadening gives information about the nature and rate of the relaxation. We will discuss both qualitative and quantitative effects below. 

Fig. 1. Atomic cascade in antiprotonic hydrogen. The hadronic interaction is observed by a level shift and a broadening of the low-lying atomic levels as compared to the calculated binding energies and radiative decay widths assuming a pure electromagnetic interaction...

When increasing temperature (T > 2 K), so introducing thermal disorder, the structure broadens rapidly. For each bulk reflectivity spectrum at a given temperature T, determining the radiative surface width by (3.26), we looked for the value of rle(T) allowing the best reproduction of the experimental spectrum. The various values obtained for re(T) vs T are plotted in Fig. (3.13) and compared with the width of the bulk exciton obtained by KK analysis (in Section II.C.3).70127... 

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