Spectral emissivity definition

The definitions of the four emissivities are brought together in Table 5.4. It additionally contains the relationships which are used in the calculation of the other three emissivities from the directional spectral emissivity a(A, / , f, T). This emissivity describes the directional and wavelength distributions of the emitted radiation flow, whilst the hemispherical spectral emissivity sx(X,T) only gives the spectral energy distribution. The directional total emissivity s (/3,f,T) only describes the distribution over the solid angles in the hemisphere. In contrast,... 

Definition and Uses of Standards. In the context of this paper, the term "standard" denotes a well-characterized material for which a physical parameter or concentration of chemical constituent has been determined with a known precision and accuracy. These standards can be used to check or determine (a) instrumental parameters such as wavelength accuracy, detection-system spectral responsivity, and stability (b) the instrument response to specific fluorescent species and (c) the accuracy of measurements made by specific Instruments or measurement procedures (assess whether the analytical measurement process is in statistical control and whether it exhibits bias). Once the luminescence instrumentation has been calibrated, it can be used to measure the luminescence characteristics of chemical systems, including corrected excitation and emission spectra, quantum yields, decay times, emission anisotropies, energy transfer, and, with appropriate standards, the concentrations of chemical constituents in complex S2unples. 

Luminescence covers all emissions of light in the near IR, VIS and near UV spectral regions. The origin of the luminescence can be specified as photoluminescence , electroluminescence , chemiluminescence , or bioluminescence for example. These definitions depend on the mode of formation of the excited molecule which eventually emits the luminescence. 

Both primary and secondary electron models (Atoyan Voelk 2000, Brunetti et al. 2001, Blasi Colafrancesco 1999, Miniati et al. 2001) have been analyzed to reproduce the spectral and spatial features of the EUV excess in Coma without a definite solution. Additional experimental information has been recently added to the complexity of the problem in particular, the EUV intensity distribution seems to be highly correlated with the thermal X-ray intensity and produce a constant ratio between the azimuthally averaged EUV and X-ray intensifies (Bowyer et al. 2004). Specific secondary models seem, at present, one of the few viable possibilities to reproduce the EUV emission features of Coma. 

The Kinetics of Absorption and Emission of Radiation.—With Bohr s picture of the relation bet ween energy levels and discrete spectral lines in mind, Einstein gave a kinetic derivation of the law of black-body radiation, which is very instructive and which has had a great deal of influence. Einstein considered two particular stationary states of an atom, say the ith and jth (where for definiteness we assume that the ith lies above the jth), and the radiation which could be emitted and absorbed in going between those two states, radiation of frequency vi7, where... 

The complexity of the ICAP emission spectra present a definite limitation to the design of an ICAP system and to the practical application to analyses (15). While this situation may be common to most or all emission spectroscopic techniques, it must be recognized in the design of ICAP instrumentation, line selection, and data review. Fortunately most spectral problems can be eliminated for most elements in most samples with the appropriate use of interference filters and computer correction techniques (10). 

The factor cos /3 that appears in (5.4) is a particularity of the definition of Lx the spectral intensity is not relative to the size dA of the surface element like in M(T), but instead to its projection dAp = cos/ dA perpendicular to the radiation direction, Fig. 5.5. It complies with the geometric fact that the emission of radiation for (3 = ir/2 will be zero and will normally be largest in the direction of the normal to the surface (3 = 0. An area that appears equally bright from all directions is characterised by the simple condition that Lx does not depend on... 

Spectral line Any of a number of lines corresponding to definite wavelengths in an atomic emission or absorption spectrum these fines represent the energy difference between two energy levels. 

The spectral overlap integral J can be expressed in terms of either wavenumbers or wavelengths (Equation 2.36). The area covered by the emission spectrum of D is normalized by definition and the quantities / and lx are the normalized spectral radiant intensities of the donor D expressed in wavenumbers and wavelengths, respectively. Note that the spectral overlap integrals J defined here differ from those relevant for radiative energy transfer (Equation 2.33). Only the spectral distributions of the emission by D /,P and, are normalized, whereas the transition moment for excitation of A enters explicitly by way of the molar absorption coefficient sA. The integrals J" and Jx are equal, because the emission spectrum of D is normalized to unit area and the absorption coefficients sA are equal on both scales. 

In contrast with this we have the hypothesis of Bohr ( 3, p. 72), according to which the atom can exist only in definite discrete states, and, at a transition from a state with the energy to a state with the smaller energy E, emits the spectral line for which liv = E — E. From the frequencies of the emission or absorption lines we can find the energies of the individual Bohr states. 

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