Síntese e propriedades fotofísicas de LOFs mistas

Abstract

In this work a series of new metal-organic frameworks containing lanthanide ions (LOFs) was synthesized by a solvothermal method at 180 0C, using terephthalic acid (1,4-H2BDC) as an organic component. Initially, three samples containing gadolinium doped with 5 mol% Eu3+ ions were prepared (Eu/Gd-1,4-BDC-MOFs). The objective of this part of the work was to study the effect of synthesis time (3, 5 and 7 days) on the morphological and luminescent properties of these materials. This study is essential because it is well known that the increase in crystallinity may lead to the decrease in reticular vibrations and, consequently, a decrease of nonradioactive relaxation channels. Subsequently, samples with different Eu3+ molar percentages (1, 3, 5, 7 and 9%) were synthesized to investigate the effect of the dopant content on the structure and photophysical properties of the LOFs. Finally, a sample co-doped with 2.5 mol% of Tb3+ and Eu3+ (Gd/Tb/Eu-1,4-BDC-MOF) was prepared and its tunable luminescent properties studied. The samples in powder form, were characterized by X-ray Diffraction (PXRD), Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR-ATR), Scanning Electronic Microscopy (SEM), Thermogravimetric Analysis (TGA) and Photoluminescence (PL). Based on the analyzes of DXRP, FTIR and PL, it was identified that materials containing up to 7 mol% of europium ions presented a single-phase. In addition, it was observed from the excitation and emission spectra that an effective intramolecular energy transfer occurred between the ligand and the Eu3+ levels, generating characteristic red luminescence of this ion. These samples emission spectra exhibited characteristic emission lines of the Eu3+ ion ascribed to the 5D0 → 7F0, 7F1, 7F2, 7F3 and 7F4 transitions. The co-doped sample presented efficient luminescent tuning resulting from the transfer of energy between Tb3+ → Eu3+. Therefore, the described materials are promising for various optical applications.