Estudo de compósitos de nanopartículas de ouro, complexo luminescente e polipirrol para potencial aplicação em sensores óptico-eletrônicos

Abstract

Metal-enhanced fluorescence (MEF) is a phenomenon characterized by changes in the spectral properties of luminescent compounds when they are near the surface of metallic nanoparticles (Nps), potentially resulting in enhanced fluorescence, increased absorption, and reduced radiative decay time. This effect is of interest for applications in optoelectronic sensors as it allows the monitoring of emission enhancement through various factors such as the size, shape, and concentration of Nps. In this study, we report the synthesis and characterization of luminescent composites based on gold nanoparticles (AuNPs) anchored or adsorbed onto the luminescent complex [Eu(tta)3(H2O)2], where tta = thenoyltrifluoroacetone, in the presence of the polymer polypyrrole (Ppy), aiming for synergy between the phases and improved properties compared to isolated components, with a view towards future applications in optoelectronic sensing and the fabrication of optical fiber-based electronic devices. The nanocomposites were synthesized by varying the amounts of pyrrole monomer, gold precursor chloroauric acid (HAuCl4), and europium complex. UV-Vis spectroscopy identified the plasmonic band of AuNPs at approximately 450 nm, as well as the absorption bands of the tta ligand (~375 nm) and the Py polymer (~250 nm). TEM images confirmed the presence of crystalline material and provided evidence that the polymer acts as a stabilizer in the formation of the Nps. X-ray diffraction (XRD) confirmed the presence of metallic nanoparticles by identifying the gold peak in the face-centered cubic phase, and through the Scherrer equation, an average size of approximately 43.9 nm was found. Emission spectra showed intra-configurational transitions of the Eu3+ ion for all sample conditions. Peaks corresponding to polypyrrole were obtained in the Raman spectra at 1591 cm-1, 1351 cm-1, and 1065 cm-1. Confocal optical microscopy images of the hybrid nanocomposites showed the presence of signals for both the europium complex and the polymer, and AFM images suggested that the presence of the complex induces changes on the sample surface, with higher peak-to-valley amplitude values compared to the surface without the complex. This study reveals potential for applications in sensing in optoelectronic devices, as MEF enables not only plasmon-based sensing by gold but also monitoring through the intensity profile and variation of intra-configurational transition wavelengths.