Enhanced luminescence of rare-earth Tb (III) obtained by mixing of Gd (III) in a fumarate complex and intra-molecular energy transfer

Trivalent lanthanide ions display fascinating optical properties. Therefore, the rare-earth complexes of terbium fumarate heptahydrate and GdTb fumarate heptahydrate were grown by using a single gel diffusion technique. The crystals were characterized by different physicochemical techniques of characterization. UV-Vis and photoluminescence spectrophotometric experiments were carried out to study the optical properties of the grown crystals. Under various excitations (339 nm, 350 nm or 368 nm) the terbium fumarate complex emitted characteristic (4f-4f) green emission of Tb³⁺ (⁵D₄-⁷F_J, J = 6, 5, 4 and 3, respectively). Luminescence spectra showed that Gd³⁺ ions in the mixed complex have not affected the luminescence emission peak positions, but remarkably increased the luminescent intensities of the terbium complex. The energy-transfer mechanism between the ligand and the central Tb³⁺ ions and from the Gd³⁺ to the Tb³⁺ was discussed.