Energy transfer between optically trapped single ligand-free upconversion nanoparticle and dye.

Area of Science:

• Materials Science
• Nanotechnology
• Spectroscopy

Background:

• Upconversion nanoparticles (UCNPs) offer unique optical properties for various applications.
• Ligand capping influences UCNP behavior in solution and during optical trapping.
• Understanding single-particle UCNP emission is crucial for developing advanced sensing platforms.

Purpose of the Study:

• To investigate the luminescence quenching of optically trapped, ligand-free hydrophilic sodium yttrium fluoride (NaYF4) UCNPs by rose Bengal dye.
• To analyze the excitation laser power-dependent emission characteristics of single UCNPs compared to bulk solutions.
• To explore the potential of these UCNPs as sensor platforms based on energy transfer studies.

Main Methods:

• Acid treatment to remove oleate capping from NaYF4:Yb, Er UCNPs.
• Fourier-transform infrared (FTIR) and Raman spectroscopy for characterization.
• Optical trapping of single UCNPs for emission studies as a function of excitation laser power and rose Bengal concentration.

Main Results:

• Single UCNP luminescence spectra showed additional lines compared to bulk solutions.
• Bulk UCNP emission indicated a two-photon upconversion process (slope 1-2).
• Optically trapped single UCNPs exhibited different power dependencies (slope <1 for Blue/Green 1, slope 1-2 for Green 2/Red).
• Rose Bengal caused concentration-dependent quenching of green emissions from single UCNPs.

Conclusions:

• Ligand removal alters single UCNP emission characteristics and power dependence.
• Energy transfer from UCNPs to rose Bengal dye demonstrates a viable sensing mechanism.
• Optically trapped, ligand-free UCNPs show promise for developing sensitive sensor platforms.