Structural, optical and phonon properties of formate-based MOF phosphors with ethylammonium cations

Abstract

We report the synthesis, crystal structure, IR, Raman and luminescence studies of four metal–organic frameworks of the following formulas: [CH₃CH₂NH₃]Y_1−x−yYb_yEr_x(HCOO)₄ (x = 1, y = 0; x = 0.2, y = 0.8; x = 0.02, y = 0.07) and [CH₃CH₂NH₃]Y_0.92Eu_0.08(HCOO)₄. All the compounds are isostructural and crystallize in a polar and non-centrosymmetric monoclinic system (P2₁ space group). They have been characterized by single crystal and powder X-ray diffraction methods as well as by vibrational spectroscopy (IR and Raman). The assignment of the external and internal modes has been discussed and presented. Furthermore, the optical properties of the Er³⁺ and Eu³⁺ ions have been assessed using diffuse absorption, excitation and emission spectra. The site symmetry of the Eu³⁺ ions has been analyzed using the emission spectrum and the luminescence decay of the red emission.