Synthesis of Ligand-Free Colloidally Stable Water Dispersible Brightly Luminescent Lanthanide-Doped Upconverting Nanoparticles

Abstract

The synthesis using the thermal decomposition of metal trifluoroacetates is being widely used to prepare oleatecapped lanthanide-doped upconverting NaYF 4 :Er 3þ /Yb 3þ nanoparticles (Ln-UCNPs). These nanoparticles have no inherent aqueous dispersibility and inconvenient postsynthesis treatments are required to render them water dispersible. Here, we have developed a novel and facile approach to obtain water-dispersible, ligand-free, brightly upconverting Ln-UCNPs. We show that the upconversion luminescence is affected by the local environment of the lanthanide ions at the surface of the Ln-UCNPs. We observe a dramatic difference of the integrated upconverted red:green emission ratio for Ln-UCNPs dispersed in toluene compared to Ln-UCNPs dispersed in water. We can enhance or deactivate the upconversion luminescence by pH and H/D isotope vibronic control over the competitive radiative and nonradiative relaxation pathways for the red and green excited states. Direct biofunctionalization of the ligand-free, water-dispersible Ln-UCNPs will enable myriad new opportunities in targeting and drug delivery applications.

Upconversion Nanocrystal‐Doped Glass: A New Paradigm for Photonic Materials

“…The removal of the ligands by a strong acid was confi rmed by FTIR spectroscopy ( Figure S6, Supporting Information). [ 29 ] The ligand-stripped NCs were vacuum dried into a powder to ease the subsequent doping of NCs.…”

Designed Er^3+-singly doped NaYF_4 with double excitation bands for simultaneous deep macroscopic and microscopic upconverting bioimaging

“…Oleate-capped NaYF 4 :30%Er 3+ @NaYF 4 :2%Er 3+ core-shell nanocrystals in hexane (or chloroform) were transferred into the aqueous phase through a modified ligand-free protocol [27,28]. This ligand-free protocol might achieve stronger overall upconversion luminescence and higher R/G ratio than the oleate-capped ones.…”

Nanophosphor Coatings: Technology and Applications, Opportunities and Challenges

“…Atoms within several lattice constants from the surface are displaced due to the surface reconstruction, and dangling bonds are often terminated by chemical species with high phonon frequencies (e.g. OH-, CO 3 -or NH-groups) adsorbed from the ambience (Bogdan et al, 2011;Igarashi et al, 2000;Liu and Chen, 2007a;Nayak et al, 2007;Ronda, 2008). The phonon spectra of nanoparticles are further modified by the introduction of surface phonon modes which are localized at the interface with surrounding medium and can provide new channels for nonradiative relaxations (Prasad, 2004).…”