Absorption and emission spectra of monomers and dimers of [tetramethoxytetrakis(octyloxy)phthalocyaninato]silicon have been measured as a function of solvent and concentration. In contrast to the monomer, the fluorescence of the dimer is shifted to lower energy by about 4000 cm -1 , and the emission quantum yield is reduced by a factor of 10 -3 . The spectroscopic data are analyzed in the strong coupling limit of dimer models and lead to an excitation exchange interaction term of 1770 cm -1 and an evaluation of the excited state lifetime of ca. 24 ps. This fast decay is dominated by nonradiative processes. The admixture of ion pair configurations is suggested to provide an efficient coupling to the environment and channel of decay of the exited state energy. Small contributions of such configurations to the ground state are also invoked to explain the marked changes in the absorption spectra as a function of environment (solvent) and concentration (aggregation).

A strong blue fluorescence has been observed following orange-yellow laser excitation in the 1D2 multiplet of Pr3+ : LaF3. This blue fluorescence has different time evolution depending on the excitation wavelength within the absorption line. Time resolved excitation techniques have been used to study this time evolution. It is shown that satellite lines, which accompany the main line, are due to ions between which energy transfer is very active. A mechanism is proposed for the observed up-conversion which is in good agreement both with our results and with observations reported by others. The nature of the interaction between the ions of the satellite lines and that of the interaction responsible for the energy transfer are discussed

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