Fig. 1. (a) Structure of 12-connected hexanuclear Eu cluster [Eu₆(μ₃-OH)₈(CO₂)₁₂]. Eu, blue; C, black; O, red. (b) Crystal structure of Eu(BDC-NH₂) viewed along the a axis. Eu, blue polyhedra; C, gray; O, red; N, blue; H atoms, Me₂NH₂ cations and free DMF molecules are omitted for clarity. (c) Powder X-ray diffraction patterns of Eu(BDC-NH₂), Tb(BDC-NH₂) and Gd(BDC-NH₂).

Fig. 2. (a) The concentration of dissolved ligand H₂BDC-NH₂ in Eu(BDC-NH₂) suspension at different time. (b) N₂ sorption isotherms of Eu(BDC-NH₂) before (red) and after (blue) being treated with water at 77 K. Solid symbols: adsorption, open symbols: desorption.

Fig. 3. Emission spectra of Eu(BDC-NH₂) in the solid state (a) suspended in THF (b) and in water (c) excited at 375 nm.

Fig. 4. (a) Emission spectra of Eu(BDC-NH₂) suspended in THF with different water content excited at 375 nm. (b) Intensities of ligand luminescence and ⁵D₀ → ⁷F₂ transition of Eu(BDC-NH₂) in the presence of various content of water. (c) The relationship of luminescence intensity ratio (I₄₃₀/I₆₁₄) and water content. (d) Luminescence intensity ratio (I₄₃₀/I₆₁₄) measured in THF/H₂O mixture with given water content (0.5, 1 and 2 vol%) using different amounts of Eu(BDC-NH₂) (0.5, 1.0 and 1.5 mg).

Fig. 5. (a) CIE chromaticity coordinates of the luminescence color of Eu(BDC-NH₂) in THF with different water content (c = 0, 0.01, 0.04, 0.1, 0.3, 0.5, 0.7, 1, 1.5, 2, 3, and 5 vol%, respectively). Photographs of Eu(BDC-NH₂) in (b) THF and (c) EtOH with different water content excited at 365 nm.

Fig. 6. (a) Schematic representation of energy transfer process in Eu(BDC-NH₂). (b) Phosphorescence spectra of Gd(BDC-NH₂) at 77 K excited at 375 nm in frozen THF and water.