Comment on “Two pathways for photon upconversion in model organic compound systems” [J. Appl. Phys. 101, 023101 (2007)]

This Comment notes that Baluschev et al. [J. Appl. Phys. 101, 023101 (2007)] have used an inappropriate model to describe photon upconversion by triplet-triplet annihilation and electronic energy transfer in metalloporphyrin-organic electronic energy acceptor systems. Models that account for aggregation of the metalloporphyrins and coaggregation of the metalloporphyrins with the organic energy acceptors must be employed. Several additional pathways for photon upconversion involving excitons in aggregates are proposed. Heterospecies triplet-triplet annihilation must be considered in the coaggregated metalloporphyrin-diphenylanthracene system.