ABSTRACT
Upconverting nanoparticles are essential in modern photonics due to their ability to convert infrared light to visible light. Despite their significance, they exhibit limited brightness, a key drawback that can be addressed by combining them with plasmonic nanoparticles. Plasmon-enhanced upconversion has been widely demonstrated in dry environments, where upconverting nanoparticles are immobilized, but constitutes a challenge in liquid media where Brownian motion competes against immobilization. This study employs optical tweezers for the three-dimensional manipulation of an individual upconverting nanoparticle, enabling the exploration of plasmon-enhanced upconversion luminescence in water. Contrary to expectation, experiments reveal a long-range (micrometer scale) and moderate (20%) enhancement in upconversion luminescence due to the plasmonic resonances of gold nanostructures. Comparison between experiments and numerical simulations evidences the key role of Brownian motion. It is demonstrated how the three-dimensional Brownian fluctuations of the upconverting nanoparticle lead to an "average effect" that explains the magnitude and spatial extension of luminescence enhancement.
ABSTRACT
Considering the structural design of some of the scarce molecular-based Er-centred emitters in the literature, we explored the optical properties of three ErIII hexaazamacrocyclic complexes, namely Er-EDA (1), Er-OPDA(2) and Er-DAP(3). The macrocyclic ligands in these complexes differ in the lateral spacers, and are derived from 2,6-pyridine-dicarbaldehyde and ethylenediamine (EDA), ortho-phenylenediamine (OPDA) or 1,3-diaminopropane (DAP). Upon ligand-centred excitation, the bluish-green and green emissions of the ErIII ion were detected only for the complexes containing macrocycles with aliphatic spacers (1 and 3), which evidenced that these ligands can sensitize the ErIII luminescence. On the other hand, the ligand derived from the aromatic diamine (2) does not sensitize the ErIII luminescence. Energy transfer mechanisms, temperature sensing, CIE coordinates and CCT values were analyzed. Besides the excitation in the ligands, the erbium-centred excitation at 980 nm allowed the detection, in all cases, of bluish-green, green and red up-converted emissions, and also the downshifted NIR emission. The possible mechanisms involved in these transitions were described and analyzed according to the available data.
ABSTRACT
A luminescent inorganic-organic hybrid material was synthesized by covalent immobilization of a europium bipyridine carboxylate complex on the inner pore walls of the mesoporous silica host MCM-41 using the grafting method. Guest-host binding was achieved through double functionalization of the host surface with organosilane reagents (trimethylsilyl, TMS, and aminopropyltriethoxysilane, APTES) followed by reaction of the active amino sites of the APTES residue with the ligand 2,2'-bipyridyl-6,6'-dicarboxylic acid. Addition of EuCl3 solution dissolved in ethanol results in the formation of an immobilized complex having the probable formula Eu(L)x(3 ≥ x ≥ 1)(H2O)y, whose detailed photophysical properties were investigated. In the final step, an additional 2,2'-bipyridine-6 monocarboxylic acid ligand was added in an attempt to complete the coordination sphere of the rare earth ion. Each of the synthesis steps was monitored by (1)H, (13)C, and (29)Si solid state NMR spectroscopies, allowing for a quantitative assessment of the progress of the reaction and the influence of the paramagnetic species on the spectra. Based on these data and additional characterizations by chemical analysis, thermogravimetric analysis (TGA), N2 sorption, X-ray diffraction and FT-IR spectroscopy, a comprehensive quantitative picture of the covalent binding and complexation process was developed.
