Lanthanide-Doped NaYF₄ Nanocrystals in Aqueous Solution Displaying Strong Up-Conversion Emission

Abstract

NaYF4:Yb3+,Er3+ nanocrystals showing high colloidal solubility in water have been obtained by treating the nanocrystals with 1-hydroxyethane-1,1-diphosphonic acid (HEDP). HEDP attaches to the surface of the nanoparticles and leads to well-separated particles in aqueous solution as verified by IR spectroscopy and dynamic light scattering measurements. In addition, the surface modification with HEDP increases strongly the up-conversion efficiency of powders and aqueous colloidal solutions of the nanocrystals. These attractive features, above all the hydrophilic nature of the nanoparticles, should make them suitable especially for bio-applications.

Progress on lanthanide-based organic–inorganic hybrid phosphors

“…Generally, the surface of the nanocrystals is covered by hydrophobic capping ligands (such as oleic acid, OA), which are not suitable for many biomedical and biological applications. 18 Moreover, the quantum yield values of the NPs experience a significant reduction relative to those of the corresponding bulk materials (e.g. 0.20 for YVO 4 : Eu 15 and 0.003 for NaYF 4 : Er,Yb 19 NPs, instead of 0.70-0.90 and 0.03 for the respective bulks).…”

“…19 Therefore, surface modification of ligand-grafted inorganic Ln 3+ -based NPs is crucial to improve their luminescence quantum yield, dispersibility and stability in aqueous solvent, and biocompatibility. [13][14][15]18 Pure blue, green and red emission colours were broadly reported in the last few years also using ligand-decorated upconversion (UC) nanocrystals. UC nanocrystals are luminescent nanomaterials that convert NIR excitation into visible emission (two low energy photons are ''added up'' to give one high energy photon).…”

Large Enhancement of Upconversion Luminescence of NaYF4:Yb3+/Er3+ Nanocrystal by 3D Plasmonic Nano‐Antennas

“…Today, one of the most effi cient lanthanide-ion-based UCL materials is the Er 3 + doped hexagonal phase NaYF 4 crystal sensitized by Yb 3 + ions (i.e., the Yb 3 + ions collect the pumping light and trasfer the energy to Er 3 + ions, which then upconvert photon enery via the lone-lived ladder-form energy levels). [18][19][20][21][22] In this energytransfer (ET) process, the UCL effi ciency depends on the light collection effi ciency of the sensitizers (i.e., Yb 3 + ions); it is therefore possible to improve the UCL effi ciency by using metal nanostructures, which can further enhance the optical absorption cross-section of the sensitizers.…”

A facile single-step procedure for the synthesis of luminescent Ln3+:YVO4 (Ln=Eu or Er+Yb)-silica nanocomposites

“…6). This behaviour might be explained by the same reasons responsible for the intensity increase [25], [26], [27], [28], [29], [30], [31] and [32], and related to a reduction in the efficiency of the non-radiative channels that populate the 4F9/2 (Er3+) level upon calcination, and therefore, in an enhanced luminescence efficiency of the green emissions.…”