Low-power photon upconversion in organic glasses

Green-to-blue upconverting molecular glasses consisting of a metal octaethylporphyrin (MOEP, M = Pd, Pt) sensitizer and 9-(4-hydroxy-methylphenyl)-10-phenyl anthracene (DPA-CH2OH) as an emitter are reported. In these materials, incident light is transformed into higher-energy radiation by way of triplet-triplet annihilation upconversion. The DPA-CH2OH-MOEP mixtures form transparent glasses when cooled from the thermally stable melt, even at rates as low as 1 degrees C min(-1). In a systematic study, the PdOEP concentration was varied from 0.025 to 6.6 mol%. The normalized upconverted light intensity decreased with increasing sensitizer concentration by almost three orders of magnitude, as a result of sensitizer aggregation. The upconverted light intensity also decreased upon deliberate crystallization of the upconverting materials. Beyond demonstrating the first embodiment of upconversion in molecular glasses, the results highlight the importance of morphology control in solid-state upconverting materials.