Effect of ligandʹs donor-acceptor properties on vibronic spectra of europium β-diketonates

The luminescence and excitation of luminescence vibronic spectra of the tris and tetrakis forms of europium β-diketonates, including ones with 1,10-phenanthroline derivatives, have been investigated. Compounds under investigation differed in the radicalʹs donor-acceptor properties of both ligands. A redistribution of the intensity in the vibronic sidebands at the change of effective charges on atoms in the nearest surroundings of Eu3+ and at the change of π-electronic density in the chelate ring of β-diketone on variation of the ligandʹs substituents has been observed. It is found that the intensity of the vibronic bands in the 100–550 cm−1 region attributed to vibrations ν (M-N) and ν(M-O) with participation of chelate ring changes. A dependence of the Stark splitting of the electronic transitions of Eu3+ ions on the donor-acceptor properties of the ligands has been examined.