Criterion of applicability of the molecular model to the interpretation of lanthanide compound electron-vibrational spectra

Experimental data permitting to determine legitimacy of using a molecular model when interpreting electron-oscillating (EO) spectra of lanthanide compounds (f-f - transitions) are presented. EO, IR and Raman spectra of compounds activated by Eu3+ and having different width of phonon bands are considered. Spectra of the series of isostructural compounds at variation of the atomic number of a lanthanide ion of the crystal matrix and spectra of the series of solid solutions of europium and yttrium compounds are studied. It is show that while behaviour of EO, IR and Raman spectra of these series for compounds with wide phonon bands is the same, it is different for compounds with narrow phonon bands. The band of valence vibration ''metal-ligand'' in IR and Raman spectra of the latter depends on mass of the metal ion of the crystal matrix and its behaviour in the system of solid solutions is two-mode. Position of this band in Eu3+ EO spectra is independent of mass of the metal ion of the crystal matrix and ratios of metal quantities in the series of solid solutions, that is regarded as a criterion for applicability of the molecular model when describing EO spectra of lanthanide-compounds