DELAYED EMISSION OF CHLOROPHYLL A AGGREGATES AND RHODAMINE 6G EMBEDDED IN POLYMER MATRIX

Delayed luminescence (in the microsecond time range) of the chlorophyl l (Chi) a ''dry'' form as well as hydrated dimers located in a polyvin ylalcohol film was measured from room temperature down to 8 K. In the same matrix the delayed luminescence of rhodamine 6G (Rhod) was invest igated. The delayed emission both of Chl a and Rhod is probably due to the formation and delayed recombination of a radical pair. It seems t hat this process occurs without participation of triplet states, as it does not reflect their well-known sensitivity to oxygen. The temperat ure dependence of the delayed luminescence of various Chl forms is dif ferent. In the region around 678 nm (dry monomer) delayed luminescence needs a thermal activation energy of about 0.03 eV, whereas at 740 nm (wet aggregates) delayed luminescence intensity increases linearly wi th decreasing temperature. Its assignment as or-type delayed luminesce nce from the low-lying triplet state can consistently be excluded from both the weak temperature dependence of the delayed fluorescence and its large intensity as compared to the prompt fluorescence. Delayed lu minescence of Rhod is almost independent of temperature between 8 K an d 300 K. The dependence of delayed luminescence intensity on exciting light intensity is linear at lower intensities and tends to saturation at higher. Therefore the delayed luminescence is not related to excit on annihilation. Positions and intensities of the Chl delayed luminesc ence bands show that it is not phosphorescence (beta-type delayed lumi nescence). The aggregation of both Chl and Rhod molecules strongly inf luences delayed luminescence since it differs in several properties if excited in the monomer or in the aggregate absorption range. Every ag gregational form of dye emits its characteristic delayed luminescence band.