I found that the emission of a dye is almost same in emission intensity (2 nm red shift) in polymer solution whereas, emission is almost 4 times enhanced in polymer thin film (40 nm) in presence of Ca2+ ion (3 nm red shift). Dye has a binding site (-COOH) and polymer is water soluble. What is the reason?
Many flexible molecule have enhanced emission in rigid environment. This is simply due to restriction of flexible motions which leads to non-radiative deactivation (loose bolt effect). It also needs to taken into consideration that the sample is thin film and getting an accurate fluorescence intensity and quantum yield may be problematic (unless an integrating sphere is used). Lifetime will be a better parameter here. 2-3 nm Stokes shift is not significant enough.
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