Absorption- and Excitation-Modulated Luminescence of Pr³⁺, Nd³⁺, and Lu³⁺ Compounds with Dianions of Tetrafluoroterephthalic and Camphoric Acids

The luminescence of coordination polymers of Pr³⁺, Nd³⁺, and Lu³⁺ with tetrafluoroterephthalate and camphorate, [Ln₂(Fbdc)₃(DMF)₂(H₂O)]₂ (Ln = Pr, Nd, Lu) and [Ln₂(Camph)₂(NO₃)₂(MeOH)]₄ (Ln = Pr, Nd, Lu), was studied. Ligand-centered and/or metal-centered emissions appear, which depend on the excitation wavelength, ultimately allowing the emitted light color to be adjusted. Low-efficiency ligand-to-metal energy transfer leads to a difference between the excitation spectra of the tetrafluoroterephthalate- and camphorate-Pr³⁺ compounds, arising from a primary filtering effect on the ligand-centered excitation, by Pr³⁺ absorption. A secondary inner filter effect significantly changes the shape of the luminescence band, allowing a wide variation in the emission color, producing, for instance, a purple color, which is not the normal spectral emission. The low-efficiency energy transfer renders tetrafluoroterephthalate and camphorate ineffective as traditional “antenna” ligands for Pr³⁺ and Nd³⁺.