Red-Emitting Hybrid Based on Eu³⁺-dbm Complex Anchored on Silica Nanoparticles Surface by Carboxylic Acid for...

Luminescent organic-inorganic hybrids containing lanthanides (Ln³⁺) have been prominent for applications such as luminescent bio-probes in biological assays. In this sense, a luminescent hybrid based on dense silica (SiO₂) nanospheres decorated with Eu³⁺ β-diketonate complexes using dibenzoylmethane (Hdbm) as a luminescent antenna was developed by using a hierarchical organization in four steps: (i) anchoring of 3-aminopropyltriethoxysilane (APTES) organosilane on the SiO₂ surface, (ii) formation of a carboxylic acid ligand, (iii) coordination of Eu³⁺ to the carboxylate groups and (iv) coordination of dbm^- to Eu³⁺. The hybrid structure was elucidated through the correlation of thermogravimetry, silicon nuclear magnetic resonance and photoluminescence. Results indicate that the carboxylic acid-Eu³⁺-dbm hybrid was formed on the surface of the particles with no detectable changes on their size or shape after all the four steps (average size of 32 ± 7 nm). A surface charge of -27.8 mV was achieved for the hybrid, assuring a stable suspension in aqueous media. The Eu³⁺ complex provides intense red luminescence, characteristic of Eu³⁺⁵D₀→⁷F_J electronic transitions, with an intrinsic emission quantum yield of 38%, even in an aqueous suspension. Therefore, the correlation of luminescence, structure, particle morphology and fluorescence microscopy images make the hybrid promising for application in bioimaging.