Local temperature of fluorescent centres in polymer films determined from universal Kennard-Stepanov relation between absorption and fluorescence spectra

Based on the Kennard-Stepanov relation between the extinction coefficient a nd fluorescence intensity in their overlapping region, local temperatures T * are determined for several dyes and stilbene derivatives in PVA and PVC p olymers. It is found that excitation energy excess for <(nu)over tilde>(exc )><(nu)over tilde>(0-0) causes local heating in a rigid polymer, and the te mperature difference Delta T = T* - T holds during the emission process. Su ch a behaviour results from slow geometrical relaxation in a polymer. Excit ation energy excess is also evidenced by the fact that the intensity distri bution in the emission band depends slightly on the excitation wavelength. This effect is stronger for higher energy excess.