Origin of broad visible luminescence in poly[methyl(phenyl)silylene] thin films

The luminescence spectrum of poly[methyl(phenyl)silylene] (PMPSi) thin films shows a strong narrow peak at 353 nm, which is of excitonic nature (related to (sigma*-sigma) transitions), and a broad emission peak with the maximum located at around 470 nm, which is related to polymer branching, charge-transfer transitions, and defect states (backbone scission). The exciton photoluminescence band strongly decreases when photodegradation of the main Si chain occurs. At the same time, new traps for holes 0.45 eV deep are formed. Their formation causes the shift of the blue visible photoluminescence observed for virgin PMPSi film into the light-green region. This effect, which is associated with the interaction of intramolecular charge-transfer excitons with trapped holes, is reversible-the reverse shift from the light-green back to blue region follows the thermal trap annealing. The decay of isothermal recombination luminescence can be described by a power function I(ITRL)similar toAt(-m). The non-monotonic temperature dependence of the exponent m is explained by peculiarities of energetic relaxations of photogenerated charge carriers and their subsequent recombination in a disordered medium. (C) 2002 Elsevier Science B.V. All rights reserved.