Organic solid-state fluorescence emission

The second section deals with the dynamics of organic primary ammonium salts of carboxylic acids, sulfonic acids, and phosphonic acids. Inspired by the steroidal crystals described above, our research has been extended to the supramolecular properties of organic salts. We focus on the latest research on solid-state fluorescence emission and pseudo-cubic hydrogen bonding clusters. It is noteworthy that the salts have practical advantages, including the relatively simple preparation oftheir crystals,... 

There is some difference of opinion about the ability of 2,2 -bipyridine to fluoresce. 2,2 -Bipyridine is weakly fluorescent in the solid state but has been reported not to fluoresce in a variety of organic solvents, although weak emissions have been obtained in cyclohexane and ethanol. 

The details of the scintillation process are complicated and depend very much on the molecular structure of the scintillator. In organic crystals, the molecules of the organic solid are excited from their ground states to their electronic excited states (see Fig. 18.18). The decay of these states by the emission of photons occurs in about 10-8 s (fluorescence). Some of the initial energy absorbed by the molecule is dissipated as lattice vibrations before or after the decay by photon emission. As a result, the crystal will generally transmit its own fluorescent radiation without absorption. 

However, it has been found that some organic compounds that are non-emissive or only weakly emissive in solution become highly emissive upon formation of aggregates, or in the solid state. In 2001, Tang and coworkers reported that a non-fluorescent silole derivative 1 in solution showed intense emission upon formation of aggregates (Scheme 1). 

Although many fluorescent organic dyes suffer serious concentration quenching in the solid state, novel types of luminophore showing intense solid state emission have developed in recent decades hy taking advantage of the frozen conformation. 

UC occurs in various ion-doped solids such as crystals [6,7] and glasses [8-11]. Usually lanthanide (4f), actinide (5f) and transition metal (3d, 4d, 5d) ions can produce UC fluorescent emission when embedded in solids or organic ligand. Of these, trivalent lanthanides based UC are predominantly used. This is because lanthanides have more than one metastable state (except Yb +) which makes them best suited... 

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