808 nm driven Nd 3+

The in vivo biological applications of upconversion nanoparticles (UCNPs) prefer excitation at 700-850 nm, instead of 980 nm, due to the absorption of water. Recent approaches in constructing robust Nd3+ doped UCNPs with 808 nm excitation properties rely on a thick Nd3+ sensitized shell. However, for the very important and popular Frster resonance energy transfer (FRET)-based applications, such as photodynamic therapy (PDT) or switchable biosensors, this type of structure has restrictions resulting in a poor energy transfer. In this work, we have designed a NaYF4:Yb/Ho@NaYF4:Nd@NaYF4 core-shell-shell nanostructure. We have proven that this optimal structure balances the robustness of the upconversion emission and the FRET efficiency for FRET-based bioapplications. A proof of the concept was demonstrated for photodynamic therapy and simultaneous fluorescence imaging of HeLa cells triggered by 808 nm light, where low heating and a high PDT efficacy were achieved

Unravelling Size-Dependent Upconversion Luminescence in Ytterbium and Erbium Codoped NaYF4 Nanocrystals

The size of the lanthanide upconversion nanocrystals significantly impacts their luminescence properties, yet the underlying mechanisms remain unclear. In this work, we undertake a systematic examination of the size effects in the commonly studied hexagonal phase sodium yttrium fluoride (beta-NaYF4) nanocrystals codoped with ytterbium and erbium ions and their core-shell structure. We demonstrate the coexistence of surface quenching and finite-size-dependent energy transfer mechanisms, quantify the effects of size-dependent surface quenching and finite-size-dependent energy transfer, and determine an interaction energy transfer distance limit of similar to 8.8 nm. A proposed theoretical model for the interplay between the two underlying mechanisms is shown to predict the experimental observations of size-dependent upconversion luminescence. Our findings provide a clear and fundamental understanding of the size effects on lanthanide upconversion luminescence at the nanoscale, thereby giving important implications for a variety of applications ranging from bioimaging and nanothermometry.</p

Internal OH− induced cascade quenching of upconversion luminescence in NaYF4:Yb/Er nanocrystals

AbstractInternal hydroxyl impurity is known as one of the main detrimental factors affecting the upconversion (UC) efficiency of upconversion luminescence (UCL) nanomaterials. Different from surface/ligand-related emission quenching which can be effectively diminished by, e.g., core/shell structure, internal hydroxyl is easy to be introduced in synthesis but difficult to be quantified and controlled. Therefore, it becomes an obstacle to fully understand the relevant UC mechanism and improve UC efficiency of nanomaterials. Here we report a progress in quantifying and large-range adjustment of the internal hydroxyl impurity in NaYF4 nanocrystals. By combining the spectroscopy study and model simulation, we have quantitatively unraveled the microscopic interactions underlying UCL quenching between internal hydroxyl and the sensitizers and activators, respectively. Furthermore, the internal hydroxyl-involved UC dynamical process is interpreted with a vivid concept of “Survivor effect,” i.e., the shorter the migration path of an excited state, the larger the possibility of its surviving from hydroxyl-induced quenching. Apart from the consistent experimental results, this concept can be further evidenced by Monte Carlo simulation, which monitors the variation of energy migration step distribution before and after the hydroxyl introduction. The new quantitative insights shall promote the construction of highly efficient UC materials.</jats:p