Excited state lower

In a review of the electronic structures and spectroscopy of linear polyenes, Hudson and Kohler have summarized the data available on the photochemical and photophysical parameters of a wide range of molecules, including aco-di-phenylpolyenes, retinals, and retinols.62 The role of an excited state lower in energy than the XBU state in polyenes does reconcile some of the anomalies in the fluorescence parameters of polyenes. There is clearly a need for a better theoretical 46 47 48... 

A close resemblance of the emission of M-phenl(c) with that of phenl(c) suggests that the IL excited state, lower-lying in energy than that of the MLCT excited state, is the predominant emissive state. 

Molecular excited state Lower state + photon (fluorescence)... 

If the exciton encounters a species with an excited state lower than its own ( AE /kT >> 1, where AE is the energy gap) the exciton can become trapped by energy transfer. In addition to the possible inclusion of chemically distinct traps along the pol nner chain, the exciton can self-trap by formation of an excimer state, e.g. 

In the cascade decay of a laser-excited state, lower-lying states are populated as illustrated in the figure for the case of alkali atoms. This provides further possibilities for laser spectroscopy investigations. 

Figure 1. Upper figure attenuation curves for F produced from CFf by electron bombardment. Neon was the attenuating gas. The ion source pressure was 20 and the F ion energy was 15 eV. The electron energy was 100 eV (Q), 80 eV 60 eV (A), and SO eV (S7). E represents the attenuation of ions in the excited state. Lower figure atenuation of F in neon when the F ions are produced by electron bombardment of a 70%-30% CFf-NO mixture. AU other parameters were the same as for the upper figure.

A fundamental issue concerning the emission efficiency relates to the control of nonradiative decays (NRDs) for Ln excited states. Lowering NRD can be achieved by locating the active ion in a low-phonon host and in this way, different Er -doped metal oxides have also been obtained by the SGM. Nb20s [30], ZrOa-HfOi [31-37], TajOs [38,39], AI2O3 [40], SnOi [41], TiOi [29,42], and... 

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