Strain-induced modification of optical selection rules in lanthanide-based upconverting nanoparticles.

Area of Science:

• Materials Science
• Nanotechnology
• Photonics

Background:

• Sodium-yttrium fluoride (NaYF4) nanoparticles are crucial for upconversion, but suffer from low quantum efficiencies.
• Low efficiency stems from parity-forbidden optical transitions and suboptimal ion spacing in lanthanide-based upconverters.

Purpose of the Study:

• To investigate the impact of pressure-induced lattice distortion on NaYF4:Yb(3+),Er(3+) nanoparticle upconversion efficiency.
• To explore modifying optical transition probabilities and ion separation through controlled lattice modifications.

Main Methods:

• Utilized pressure-induced lattice distortion to systematically alter nanoparticle structure.
• Employed in-situ X-ray diffraction to monitor lattice constant changes under pressure.
• Measured upconversion emission intensity to quantify efficiency changes.

Main Results:

• Hexagonal-phase NaYF4 nanoparticles showed a decrease in upconversion emission under pressure.
• Cubic-phase NaYF4 nanoparticles exhibited a significant, nearly 2-fold increase in upconversion efficiency.
• Observed efficiency changes in cubic-phase particles correlated with a minimal 1% reduction in lattice constant.

Conclusions:

• Pressure-induced lattice distortion is an effective strategy to enhance upconversion efficiency in specific nanoparticle phases.
• Demonstrated a clear relationship between lattice geometry and upconversion performance in NaYF4 nanoparticles.
• This approach offers a promising pathway for optimizing quantum efficiency across various lanthanide upconverters.