An efficient synthetic strategy for ligand-free upconversion nanoparticles

Abstract

High-quality lanthanide-doped upconversion nanoparticles are generally synthesized by employing long-chain oleic acid as the ligand in the synthetic process, rendering them hydrophobic, and preferentially dispersed in nonpolar solvents. Thus, postsynthetic...

Solvothermal Synthesis of Lanthanide‐doped NaYF4 Upconversion Crystals with Size and Shape Control: Particle Properties and Growth Mechanism

“…Well‐defined UC crystals with tunable size can also be prepared via the LSS method by changing experimental parameters, like ligand amount, F − concentration, and impurity doping [13a,18] . Since these UC crystals are hydrophobic, post‐modification is often particularly for all applications involving the aqueous environment [4f] . To circumvent post‐synthetic surface modifications, the synthesis of UC particles via the hydro/solvothermal method has been done by employing hydrophilic polymers or small molecules as ligands instead of the commonly used hydrophobic ones.…”

Upconversion-based nanosystems for fluorescence sensing of pH and H2O2

“…Ligand-free UCNPs were prepared using our previously reported method. 47 5 mmol of formic acid was directly added to 2 mL of cyclohexane solution containing 20 mg of OA-UCNPs, ligand-free UCNPs were precipitated out after shaking for 10 s at 3000 rpm on a vortex mixer. Bare UCNPs were obtained after centrifugation and washing once with ethanol and three times with water and finally dissolved in water.…”

“…Ligandfree UCNPs are prepared by direct addition of formic acid to the cyclohexane solution containing OA-UCNPs through the vortexing method and sequential modication with PEI to obtain PEI-UCNPs. 47 TEM images demonstrate unchanged morphology and size aer ligand removal and polymer functionalization ( Fig. S2 †).…”

Fluorescence sensing of cyanide anions based on Au-modified upconversion nanoassemblies

“…After the treatment of OA-UCNPs with formic acid, the oleate ligand can be easily removed. 47 The obtained ligand-free csUCNPs can be well-dispersed in water to form a stable colloidal solution, and the zeta potential was determined to be 36.8 mV ( pH ∼5.5). Moreover, these well-dispersed bare csUCNPs favor the attachment of PEI on their surface.…”

“…Ligand-free upconversion NPs were prepared via a vortexing method according to our previous publication. 47 Formic acid (5 mmol) was added to 2 mL of cyclohexane solution containing OA-UCNPs (10 mg mL −1 ) directly; the mixture was then shaken for 10 s (3000 rpm) on a vortex mixer, and ligand-free UCNPs were precipitated out. The resultant NPs were obtained by centrifugation at 6000 rpm for 20 min, washed once with ethanol and three times with water, and finally redispersed in water.…”