A Search for Some Wide-Range Tunable Dye Laser Systems Working on the 'Exciplex' Principle.
NAVAL WEAPONS CENTER CHINA LAKE CALIF
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The exciplex mechanism of radiation emission from a dye affords one means of producing a broad fluorescent spectrum without adding to the absorption spectrum. It relies on a change of equilibrium properties in the excited state compared with those of the ground state, and the fluorescence is not from the same chemical species absorbing the radiation. Such a system may show a considerable displacement of the fluorescence and absorption spectra so that the threshold input power for lasing may be reduced and the range of tuning can be extended. Also, by a careful selection of conditions, emissions from both the dye and the exciplex may appear, thereby permitting an even greater tuning range. Two mechanisms apply the proton exciplex, which relates to changes in conventional acidity and basicity in the excited state and the molecular exciplex, which relates to changes in electron-acceptor and electron-donor propertiesi.e., changes in Lewis acidity and basicity. Wide tuning range blue-violet to yellow-green, 122 nanometers is reported for 4,8-dimethylumbelliferone. It is proposed that this dye operates by a double proton exciplex mechanism, wherein the molecule is both a stronger acid and a stronger base in the excited state. Peculiarities in the lasing action of 9-aminoacridine are discussed.
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