Zero-phonon transition

Fig. 7.18 The radiative recombination time r as a function of the blue shift of the photon energy AE from the bulk silicon band edge zero-phonon transitions (dots) TO phonon-assisted transitions (line). This scatter plot shows the radiative time for each member of an ensemble uniformly distributed around a cubic geometry. The top scale indicates the equivalent cube size. Redrawn from [Hy2],...

Recoilless Optical Absorption in Alkali Halides. Recently Fitchen et al (JO) have observed zero phonon transitions of color centers in the alkali halides using optical absorption techniques. They have measured the temperature dependence of the intensity of the zero phonon line, and from this have determined the characteristic temperatures for the process. In contrast to the Mossbauer results, they have found characteristic temperatures not too different from the alkali halide Debye temperatures. 

Fig. 13. Emission spectra of Ba5(P04)3Cl Mn5 + and Ca2VC>4Cl Mn5 + at 8 K. The zero-phonon transition is the dominating line on the right-hand side. The vibronic lines are assigned in terms of the Mn-O bending (5) and stretching (v) vibrations. Reproduced with permission from Ref. [45]...

The PL from PPV is quite strong, with a quantum yield in the range from a couple of percent to several tens of percent [25,26], and there is a clear evidence of vibronic structure, with the zero-phonon transition at 515 nm. The efficiency of the photoluminescence is larger when the lifetime of the singlet exciton is... 

Our first steps toward the single-molecule regime arose from work at IBM Research in the early 1980s on persistent spectral hole-burning effects in the optical transitions of impurities in solids (for a review, see [20]). Briefly, if a molecule with a strong zero-phonon transition and minimal Franck-Condon distortion is doped into a solid and cooled to liquid helium temperatures, the optical absorption becomes inhomogeneously broadened (Fig. 2.2A). The width of the lowest electronic transition for any one molecule (homogeneous width, Yjj) becomes very small because few phonons are present, while at the... 

The internal modes can be seen in Fig. 5.2(b) above 1200 cm. This region of the spectrum is very rich and again there are too many features to be explained by the two fundamentals alone. The external mean square displacement value is so big that most of the intensity arising from the internal vibrations is actually found in the phonon wings ( 2.6.5). Here the full wing is operative and includes translational and librational contributions. Indeed few of the sharp features present in this part of the spectrum are due to zero phonon transitions of the fundamentals. This is but a slightly more severe case of the analysis that will be covered in detail for benzene and we end our analysis of the pure ammonium bromide salt here. 

This process is a resonance process between matched oscillators and is non-radiative in nature. One important consequence is sometimes called "sensitized luminescence". Note that 11> has a higher energy than 2> and that there is an overlap area of energies caused by vibronic coupling broadening of the zero-phonon transition. 

Minimum to minimum transition energy. Experimental zero-phonon transition energy note that Teand Eo-o can be directly compared because the vibrational frequencies are very similar in all states. 

Since the spectroscopy of this phosphor is incorrectly described in the book on lamp phosphors [2], we add here, also as an illustration of the theory, a few comments on the spectroscopy. In view of its electron configuration (d ), the Mn ion will be octahedrally coordinated. The emission lines are tabulated in Table 6.3. There is a zero-phonon transition (Sect. 2.1) which at low temperatures is followed by vibronic lines due to coupling with the asymmetric Mn -0 deformation and stretching modes, 1/4 and 1/3, respectively. These uneven modes relax the parity selection rule. At room temperature there occur also anti-Stokes vibronics (Pigs. 6.21 and 6.22). The vibrational modes in the excited state and ground state are equal within the experimental accuracy as is to be expected for the narrow A2 transition [25,26]. The intensity ratio of the Stokes and anti-Stokes vibronic lines agrees with the Bose-Einstein distribution [26]. 

E° is identical to the zero phonon transition energy Eo o related to the a-vibration except for a correction by corresponding zero point energies ... 

If Eo-o is identified with the zero phonon transition from the experiment that includes zero point energy effects of the other (non active) modes the extra terms are included into E which also is determined from the spectra fitting the vertical transition energy to E - AE (vide infra). The shift of the excited state potential minimum with respect to that of the ground state, i.e. the equilibrium geometry distortion, is calculated from the parabolic formulas to be... 

Fig. 4. 23 The spectrum of a photochemical hole burned in the long-waveloigth absorption band of a sample of photosynthetic bacterial reaction centers at 5 K [68]. The gray curve is the difference between absorption spectra measured with the excitation laser on and off. The excitation frequency was 10,912 cm. Note the sharp zero-phonon hole PH, upward arrow) at 10,980 cm . The downward arrows indicate the centers of two discrete vibrational (phonon) bands that are linked to the zero-phonon transition. The solid curve is a theoretical hole spectrum calculated as described in the text...

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