Peculiarities of the luminescence excitation of europium and terbium substituted benzoates
Vera I. Tsaryuk, Konstantin P. Zhuravlev
Abstract
A comparative analysis of the spectroscopic characteristics of a large number of benzoates, nitro-, methoxy-, amino- and hydroxybenzoates of europium and terbium including those with an ancillary 1,10-phenanthroline ligand is presented. The effect of the stepwise introduction of substituents in the benzoate anion on the Eu 3+ and Tb 3+ luminescence excitation spectra and luminescence intensity is discussed. A combination of donor and acceptor substituents in the aromatic ring of lanthanide benzoates makes it possible to obtain intense luminophores with an excitation band extended to the visible region. Examples of such luminophores are europium nitrosalicylates having an UV-green excitation band caused by the intraligand charge transfer (ILCT). The participation of low-energy ligand-metal charge transfer (LMCT) states in the quenching of luminescence of europium substituted benzoates, in particular, amino- and hydroxybenzoates is considered. It was shown that the donor-acceptor properties of substituents and electronic substitution effects play an important role in the excitation energy transfer to the Ln 3+ ion in lanthanide benzoates.