Photoluminescence and quantum chemical studies of electronic and optical properties of m-nitroaniline and m-nitrophenol crystals

Abstract

Fluorescence, phosphorescence and their excitation spectra of single crystals of m-nitroaniline (m-NA) and of m-nitrophenol (m-NPh) were measured at 5 K. m-NA and m-NPh were also studied in an n-hexane Shpolskii matrix. Phosphorescence and phosphorescence decays were also collected at higher temperatures. On the basis of band position analysis and quantum chemical calculations the phosphorescence is assigned to the molecular emission whereas the fluorescence is supposed to originate from crystal defects—radical ions. Radical ions are photogenerated in both materials and in m-NA by crystal freezing below the glassy phase transition. Computed values of the first order hyperpolarizability, β_vec, are larger for radical ions than for neutral molecules which suggests that radical ions are intermediates in the molecular mechanism of optical nonlinearity generation.