4.8. Field-emission spectrum

Fig. 4.8. Field-emission spectrum of Mo(lOO). The quantity displayed, Jf, is the ratio between the observed field-emission current and the prediction based on a free-electron model, Eq. (4.20). As shown, the field-emission spectrum of Mo(lOO) near the Fermi level is substantially different from a free-electron-metal behavior. (After Weng, 1977.)...

Fig. 4.7. Field emission spectra of W(112) and W(IOO). Dotted curve theoretical field emission spectrum for free electron metals. Dashed curve experimental field emission spectrum for W(112). Solid curve experimental field emission spectrum for W(IOO), A substantial deviation from the free electron metal behavior is observed. The deviation, so-called Swanson hump, is due to the dominating role of localized surface states near the Fermi level at W(IOO) surface in field emission. (After Swanson and Grouser, 1967).

Figure 6.1. Jablonski-type diagram for pyrazine. The zero-field splittings (between tx, tV) t2) are not drawn to scale. Spin polarization ( x x x) resulting from the most probable intersystem crossing routes and part of the emission spectrum where different vibronic bands (v = /,/, k) have different zf origins are schematically indicated. (After El-Sayed.(17))...

As mentioned above, spectral imaging microscopy is a form of multidimensional fluorescent microscopy where a fluorescent emission spectrum is acquired at each coordinate location in the sample. This mode of imaging has been implemented for wide field, confocal, and two-photon laser scanning microscopy, and several excellent... 

The lines at 686 and 693 nm with a long decay time of approximately 1 ms in the titanite emission spectrum are not correlated with any other lines and bands (Fig. 4.34). Such lines are very typical for Cr in a high field coordination and may be connected with such a center. The broad luminescence band appears peaking at 765, which may be ascribed to Cr + in a weak field coordination. The band at 765 nm has distinct dips at 749, 762, 793, 798, 804 and 820 nm. Comparison with the titanite absorption spectrum (Fig. 5.19) demonstrates that those lines exactly coincide with the absorption spectrum of Nd (Bakhtin and Gorobets 1992). Cr is a good energy sensitizer, because it has broad, allowed absorption bands with a broad emission spectrum, which overlaps the absorption bands of the lasing ion (Nd " ", Ho " ). 

Diagrams of levels splitting in crystal fields of different symmetry are identical with those for the isoelectronic Ti " ion. An emission spectrum attributed to was found in aAl203 in the visible region at low temperatures (Champagnon and Duval 1979). It consists of broad band peaking at 625 nm and narrow lines at approximately 528 and 529 nm (Fig. 5.3lb,c). 

Equation (4.20) has been verified by a large number of metals at various temperatures, from 77 K to 900 K. Most metals conform to this equation very well. However, Swanson and Grouser (1966) found that the field-emission spectra on W(IOO) deviates substantially from Eq. (4.20). There is a pronounced peak at about 0.35 eV below the Fermi level (Fig. 4,7). This phenomenon later acquired a nickname, the Swanson hump. A series of more extensive experiments were then conducted to investigate its nature (Swanson and Grouser 1967). The main results are (1) The spectrum depends dramatically on the crystallographic orientation. On W(310), W(211), W(lll), and W(611), the measured field-emission spectra agree well with the free-electron... 

Gliemann et al. also studied the luminescence of systems with vibrational structure [31], viz. the Se4+ ion in Cs2SeCl6 and Rb2SeCl6. Figure 10 presents the emission spectrum of Cs2SeOe as a function of temperature and magnetic field. The low-temperature emission intensity increases with temperature as well... 

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