Bulk photoluminescence of molecular crystals under two-photon excitation conditions

A study is reported of the spectral characteristics of two-photon-excited luminescence of polycrystalline samples of anthracene, diphenyl, and fluorene. The luminescence spectra recorded under two-photon, one-photon, and x-ray excitation conditions were compared. Considerable differences between these spectra were found. The main factors influencing the nature of the two-photon-excited luminescence spectra are reabsorption, surface energy states, and transition from spontaneous luminescence to superluminescence.