Triplet States in Isotopically Mixed Naphthalene Crystals: High Resolution Optical Spectroscopy

Abstract

The triplet 0.0 transitions (T1↔ S0) of guest and host in various isotopically mixed naphthalene crystals, with guest states below and above the host exciton band, are investigated applying both laser excitation spectroscopy and phosphorescence emission spectroscopy. Guest monomer and aggregate spectra are analyzed at helium temperatures (1.6-4.2 K) with regard to line positions, splittings, polarizations and intensities. Shift and broadening of the host Davydov components are studied as a function of the guest concentration (at 1.6 K). In particular, the analysis provides precise values for the individual isotopic shifts U0 and the exciton band structure parameters including the critical isotopic shift. Site splitting is spectrally resolved for several monomers and also for the AB-dimer of 1,4-Nd2 in Nd8