Duel-Responsive Hybrid Nanoparticle with Energy Transfer Modulated Near Infrared Emission

Graphical A stronger NIR emission and a broadband excitation can be achieved when the nanoparticle NaYF 4 : Nd 3+ are coated by OFBT which is ascribe to the energy transformation between NPs and OFBT. The energy transfer efficiency can be modulated by the dynamic interactions of OFBT with the NP surfaces. In addition, the hybrid nanoparticles can be used as pH and temperature probes due to their duel-responsive properties. Lanthanide (Ln) activated systems are characterized by the rich line-shaped emission spectra stemming from the parity-forbidden inner shell f-f transitions. This inherent nature of Ln ions efficiently stabilizes their emissions against environment perturbations, but always necessitates the use of strong and broadband sensitizer to achieve efficient emission. Here, based on a model near-infrared (NIR) emitting system – NaYF 4 : Nd 3+ NPs, we demonstrate sensitized NIR emission by grafting the nanoparticle (NP) surfaces with a visible-light active organic conjugated oligomer, 4,7-(9,9′-bis(4-carboxybutyl)-fluorenyl)-2,1,3-benzothiadiazole (OFBT). Photoluminescence (PL) emission, excitation and time-resolved spectra confirm energy transfer from the OFBT molecules to nanoparticles across the organic/inorganic interfaces, and the efficiency of ET is quantitatively determined by the surface coverage of OFBT molecules and concentration of Ln ions in the NPs. By taking advantage of the environment-sensitive binding strength of OFBT to NP surface, we further demonstrate high sensitivity of the NIR emission from the hybrid NPs to variations in pH and temperature, which is explained by the change in energy transfer efficiency from OFBT to NPs. Therefore, the developed nano-hybrid systems are believed to have potential applications in sensing and detection in physiological environment.