Inhibiting concentration quenching in Yb³⁺-Tm³⁺ upconversion nanoparticles by suppressing back energy transfer

Area of Science:

• Materials Science
• Nanotechnology
• Photonics

Background:

• Lanthanide-doped upconversion nanoparticles (UCNPs) show potential in biosensing, bioimaging, and lasing.
• Their brightness is often limited by concentration quenching of activator ions.
• Existing UCNPs struggle with optimal activator ion concentrations due to this quenching effect.

Purpose of the Study:

• To design a novel nanostructure that mitigates lanthanide ion concentration quenching.
• To enhance the brightness and utility of UCNPs for various applications.
• To investigate the mechanisms behind improved upconversion efficiency.

Main Methods:

• Fabrication of a heterogeneous core-shell-shell nanostructure using hexagonal NaYF4.
• Spatial separation of thulium (Tm3+) activators and ytterbium (Yb3+) sensitizers into distinct layers (core and inner shell).
• Utilizing an outermost shell to minimize surface quenching effects.

Main Results:

• The core-shell-shell design significantly alleviates activator concentration quenching.
• Optimal Tm3+ concentration increased from 1% to 8% at low irradiance (sub-100 W/cm2) compared to core-only UCNPs.
• At high irradiance (20 MW/cm2), optimal Tm3+ concentration reached 50%.
• Spatial separation suppressed back energy transfer from Tm3+ to Yb3+.

Conclusions:

• The heterogeneous nanostructure effectively enhances UCNP brightness by overcoming concentration quenching.
• This design strategy provides a pathway for developing highly efficient upconverting materials.
• Findings deepen the understanding of lanthanide concentration quenching mechanisms.