Abstract
Temperature effects on the highly specific high resolution fluorescence spectra of tetracene in crystalline solutions at cryogenic temperatures have been investigated with emphasis on analytical implications. A comparison has been made between conventional non-selective broad-band excitation and laser excitation with special attention to position, height, width and shape of the peaks in the fluorescence spectrum. When lamp excitation is employed, temperature increase invariably results in a height and intensity decrease of the narrow lines. However, upon laser excitation a maximum in intensity and peak height may he observed at elevated temperatures when excitation takes place in a region where a narrow banded absorption transition occurs. Peak shapes are Gaussian under lamp excitation; laser excitation yields narrower bands with more Lorentzian character. As the temperature increases the narrow bands undergo a shift, in a similar way for both lamp and laser excitation. An explanation for these observations is presented. It is crucial that in the laser excited methods also it is the absorption step which determines the emission that is obtained. The laser probes an area with narrow absorption bands so that the intensity of the emission light is strongly influenced by the degree of matching of laser line and molecular absorption bands.
Published Version
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