Laquai, F., Wegner, G., Im, C., Büsing, A., & Heun, S. (2005). Efficient upconversion fluorescence in a blue-emitting spirobifluorene-anthracene copolymer doped with low concentrations of Pt(II)octaethylporphyrin. The Journal of Chemical Physics, 123(7): 074902. doi:10.1063/1.1992477.