NEAR-INFRARED LUMINESCENCE SPECTROSCOPY OF NICKELOCENE DOPED INTO SINGLE-CRYSTALS OF RUTHENOCENE

Single crystals of ruthenocene doped with nickelocene show a near-infr ared luminescence band with a maximum at 13 100 cm(-1) and a width of 1100 cm(-1) at 5 K in addition to the ruthenocene luminescence, The ba nd is symmetric and attributed to nickelocene on the basis of a compar ison of luminescence and absorption spectra. Energy transfer from the ruthenocene host enhances the nickelocene luminescence intensity at te mperatures between 50 and 100 K. An activation barrier of 306(18) cm(- 1) is determined from luminescence decay measurements. The Stokes shif t of 2200 cm(-1) and the large change of 0.16 Angstrom in nickel-cyclo pentadienyl distance in the emitting state confirm the assignment as ( 3)E(1g), arising from an electron configuration different from that of the ground state. The comparison of experimental and calculated spect ra shows that only low-energy vibrational modes contribute to the lumi nescence band shape, in contrast to the case of cobaltocene doped in t he same host lattice, where a distortion along a high-frequency, ligan d-centered mode affects the luminescence band shape.