The influence of Förster energy transfer on spectral and kinetic characteristics of phosphorescence and thermally activated delayed fluorescence of acriflavine in a polyvinylalcohol matrix

Spectral and kinetic characteristics of thermally activated delayed fluorescence (TADF) and phosphorescence of acriflavine in polyvinylalcohol films have been investigated. It was shown that TADF and phosphorescence decay times decrease due to fluorescence resonance energy transfer (FRET) as the concentration of the dye molecules increases. The luminescence spectra of the concentrated solutions are bathochromic shifted with respect to that of the deluted ones. Moreover, TADF and phosphorescence spectra of the concentrated solutions shift to the higher frequency region as emission decays. These effects are determined by the correlation between FRET direction and the heterogeneity of the triplet state lifetimes. Numerical simulations of the spectral and kinetic characteristics of TADF and phosphorescence were made by means of Monte-Carlo integrations, and results were compared with experimental data.