Spectra of centrosymmetric rare-earth complexes:Nd3+-hexakis-antipyrine tri-iodide single crystals

Polarized absorption spectra of centrosymmetric neodymium hexakis-antipyrine tri-iodide single crystals at 77 and 20°K have been discussed. The spectrum is complicated by the appearance of a large number of vibronic lines. A phase transition destroying the inversion symmetry occurs between 77 and 20°K and this was used as a tool to locate the 0-0 lines. Some of the 0-0 lines have been shown to be magnetic dipole allowed. The calculated crystal-field parameters (Stevens) are $B_2^0=200\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$; $B_4^0=-130\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$; $B_6^0=60\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$; $B_4^3=3250\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$; $B_6^3=1000\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$; $B_6^6=400\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$.