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The Local Temperature Dependence of Fluorescent Centres in PVA Films on the Excitation Wavenumber

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The Local Temperature Dependence of Fluorescent Centres in PVA Films on the Excitation Wavenumber

A. Kawski, P. Bojarski, and B. Kuklin´ski

Institute of Experimental Physics, University of Gdan´sk, ul.Wita Stwosza 57, 80-952 Gdan´sk, Poland Reprint requests to Prof. A. K., ul.Gen.W.Sikorskiego 11, PL-84-200 Wejherowo, Poland.

Z. Naturforsch. 55a, 653 – 655 (2000); received May 11, 2000

The temperature difference %T = T* – T (where T* is the local temperature and T the ambient tem- perature) is studied as a function of the excitation wavenumber O˜excin the longwave region of the ab- sorption band of 4-amino-4y-nitrostilbene (ANS) and 4-dimethylamino-4y-nitrostilbene (DNS) as well as rhodamine S, rhodamine 6G and Na-fluorescein in poly(vinyl alcohol) (PVA) films heated up to 403 K. Local temperatures T* are determined by a universal Kennard-Stepanov relation. A linear de- pendence of %T on O˜exchas been found for all investigated luminescent compounds. For dyes, due to the big spectral overlaps between the absorption and fluorescence bands, it was possible to excite also in the anti-Stokes region. In this case for %T = 0, i.e. when T* = T, one has O˜exc=O˜0 – 0y . In view of the slow geometrical relaxation of excitation energy excess in PVA polymers, the relaxation time τRfor thermal equilibration between the luminescent molecule and the vicinal polymer exceeds distinctly the mean fluorescence lifetime τF.

Key words: Kennard-Stepanov Universal Relation; Local Temperature; PVA Fluorescent Films.

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