PHOTOLUMINESCENCE AND QUANTUM-CHEMICAL STUDIES OF ELECTRONIC AND OPTICAL-PROPERTIES OF M-NITROANILINE AND M-NITROPHENOL CRYSTALS

Fluorescence, phosphorescence and their excitation spectra of single c rystals of m-nitroaniline (m-NA) and of m-nitrophenol (m-NPh) were mea sured at 5 K. m-NA and m-NPh were also studied in an n-hexane Shpolski i matrix. Phosphorescence and phosphorescence decays were also collect ed at higher temperatures. On the basis of band position analysis and quantum chemical calculations the phosphorescence is assigned to the m olecular emission whereas the fluorescence is supposed to originate fr om crystal defects-radical ions. Radical ions are photogenerated in bo th materials and in m-NA by crystal freezing below the glassy phase tr ansition. Computed values of the first order hyperpolarizability, beta (vec), are larger for radical ions than for neutral molecules which su ggests that radical ions are intermediates in the molecular mechanism of optical nonlinearity generation.