Magnetic-field effects in the low-temperature polarized emission and absorption spectra of single-crystal [Ru(bpy)₃](PF₆)₂

Abstract

In this paper we report on the magnetic-field dependence of the broad-band emission spectra and the zero-phonon line emission and absorption of single-crystal [Ru(bpy)₃ (PF₆)₂ at low temperatures. It is found that a magnetic field oriented with H perpendicular c induces drastic effects, whereas H parallel c does not change the emission and absorption properties. At T = 2 K an increase of the total emission intensity by a factor of 6 is observed under the action of a magnetic field H = 6 T. The zero-phonon lines corresponding to the two lowest excited states exhibit a Zeeman effect, the energy separation growing from 7 cm⁻¹ at zero field to 13 cm⁻¹ at H = 6 T. Furthermore, the magnetic field changes the (temperature-dependent) ratio of the intensities of the zero-phonon emission lines by more than two orders of magnitude up to H = 6 T, the intensity of the lower energy line increasing while that of the higher energy line decreases. In absorption only the higher energy zero-phonon line is detectable in the absence of a magnetic field. Strong magnetic fields, however, induce the lower energy absorption line and cause the same Zeeman shift as in emission. The positions of the zero-phonon lines coincide in absorption and emission. All these experimental results are explained by magnetic-field-dependent mixing of the wave functions of the two lowest excited states. A simple perturbation calculation is presented to rationalize the experimental results.