| Abstract [eng] |
Light upconversion via sensitized triplet-triplet annihilation (TTA-UC) allows to upconvert lower energy photons to higher energy at relatively low excitation power densities (~10 mW/cm2). This feature is very attractive to enhance the performance of solar cells and organic light emitting diodes and for bio-imaging applications. The quantum yield of light upconversion in solution is up to ~30%, while in solid films, which is more desirable for practical applications, quantum yield dramatically decreases. This decrease in upconversion quantum yield is attributed to strong aggregation induced quenching, which could be partially solved by preparing films via melt processing. In addition, homogeneity of the films could be enhanced by increasing structural disorder in the system by utilizing two types of emitters. The employment of binary system is also believed to enhance upconversion quantum yield due to synergistic effect, which was demonstrated to work for upconversion in solution. The aim of this work is to perform detailed photophysical characterization of binary system of dimesitil- and diphenylanthracene solid polymer films and determine optimal conditions for light upconversion. For this study, upconverting films based on sensitizer platinum octaethylporphyrin and binary system of diphenyl- and dimesitilanthracene compounds in PMMA were fabricated by melt processing technique in inert atmosphere. Upconversion of polymer films were evaluated by measuring fluorescence, phophorescence and light upconversion spectra, decay transients and estimating their quantum efficiencies. The obtained data showed no synergistic effect in this binary system of dimesitil- and diphenylanthracene in solid polymer films, because in these films, the of triplet-tiplet excitons annihilation occurs mainly in the dimesitilantracene molecules, therefore quantum efficiency of light upconversion does not exceed the yield, which is achieved in diphenylanthracene mono-emitter films. However, the highest quantum efficiency of light conversion in mono-emitter polymer films is achieved at the same concentration for both diphenyl and dimesitilantracene emitters indicating that singlet and triplet exciton quenching is also the same in these compounds. Additionally, lower light conversion efficiency of 2.8% obtained for dimesitilantracene films as compared to diphenylanthracene is due to the increased singlet exciton non-radiative relaxation rate in DMA molecules. |
