Charge transfer and f-f transitions studied by photoacoustic spectroscopy of [R(NO₃)₂(PicBH)₂]NO₃ and [R(NO₃)₃(PicBH)₂] complexes (R - Rare earth ion)

High-resolution photoacoustic spectra of trinitrate-bis[N-(2- pyridylmethylene)-N′-benzoyl-hydrazine]R(III), (R = La, Cc, Pr), and binitrato-bis[N-(2-pyridylmethylene)-N′-benzoyl-hydrazine]R(III) nitrate (R=Y, Nd, Eu, Yb, Tb, Gd, Ho, Dy, Er) complexes, in the visual region, were studied for powder samples. Very intense photoacoustic spectra of various shapes were attributed to the intraligand transitions of the π → π* type located mainly on the C=N group and the n → π* transitions located on the carbonyl group. The intensity of these transitions essentially depends on the type of rare earth ions. The existence of f-f electron transitions could influence the relaxation processes, which play an important role in intensity determination of the above transitions. For many investigated samples the energy levels of excited states of rare earth ions were identified (f-f electron transitions). The radiation energy for some of the rare earth ions were compared with the d-d electron transitions of certain coppcr(II) organometallic complexes, which are very important in biogenic systems. The correlation between ions with localized and extended wave functions is suggested.