Adding More Shape to Nanoscale Reference Materials─LiYF₄:Yb,Tm Bipyramids as Standards for Sizing Methods and...

Area of Science:

• Materials Science
• Nanotechnology
• Analytical Chemistry

Background:

• Industrial use of nanomaterials necessitates reliable characterization of physicochemical properties.
• Nanoscale reference materials (nanoRMs) are crucial for validating characterization methods.
• Upconversion nanoparticles (UCNPs) are promising candidates for nanoRMs due to their tunable properties and inertness.

Purpose of the Study:

• To explore the potential of LiYF4:Yb,Tm UCNP bipyramids as size standards for small-angle X-ray scattering (SAXS).
• To utilize UCNPs for validating simulations of SAXS data from nonspheric nanoparticles.
• To establish traceable particle number concentration measurements for ligand-capped nonspheric particles.

Main Methods:

• Synthesis of monodisperse LiYF4:Yb,Tm UCNP bipyramids.
• Small-angle X-ray scattering (SAXS) measurements for size determination and particle number concentration.
• Two-dimensional transmission electron microscopy (2D-TEM) for structural analysis.
• Gravimetry, thermogravimetric analysis (TGA), and inductively coupled plasma optical emission spectrometry (ICP-OES) for complementary measurements.

Main Results:

• UCNP bipyramids with peak-to-peak distances of (43 ± 2) nm and (29 ± 2) nm were prepared.
• SAXS measurements successfully used UCNPs as size standards.
• Traceable particle number concentration was determined for cyclohexane dispersions of UCNPs.
• Multitechnique approach validated particle concentration measurements for challenging samples.

Conclusions:

• Lanthanide-based UCNPs are effective multimethod nanoRMs for nanomaterial characterization.
• UCNPs facilitate the standardization of SAXS methods for nonspheric nanoparticles.
• The developed approach enables accurate and traceable particle number concentration measurements, even for particles with unknown composition.