MATRIX-INDUCED 2-PHOTON ABSORPTION IN ANTHRACENE

The absorption spectrum and the two-photon excitation spectrum of anthracene in a carbazole matrix have been measured at 1.8 K in the wavelength range of the first absorption band near 400 nm. This transition is formally allowed as a one-photon but not as a two-photon process; however, two-photon intensity is induced into the anthracene spectrum by the matrix. The intensity distribution along a Franck-Condon progression is not the same in the one- and two-photon spectra. Assuming that the vibronically induced component of the two-photon spectrum is independent of the host, earlier intensity data taken in a fluorene host crystal can be scaled to the new data collected here. A simple model, set up in the deep trap limit, is used to account for these observed differences between the one- and two-photon spectra in the carbazole host and between fluorene and carbazole host materials.