Enhancement of Upconverted Fluorescence by Interference Layers

Area of Science:

• Nanotechnology
• Optics
• Materials Science

Background:

• Upconverting nanoparticles (UCNPs) are promising for photovoltaics and detection.
• Interference-based fluorescence enhancement is known for Stokes-shift systems.
• The effect of interference on nonlinear Anti-Stokes emission in UCNPs is unexplored.

Purpose of the Study:

• To demonstrate and detail the influence of interference geometry on nonlinear upconversion emission.
• To investigate the impact of interference on excitation and radiative/nonradiative decay processes.
• To optimize UCNP emission through controlled interference layer thickness.

Main Methods:

• Fabrication and characterization of UCNPs with varying interference layer thicknesses.
• Single-particle spectroscopy and time-resolved measurements.
• Finite element modeling (FEM) for correlation with experimental results.

Main Results:

• Demonstrated interference modulation effects on excitation (energy transfer) and decay dynamics.
• Observed thickness-dependent decay rates and rise times.
• Achieved significant emission enhancement (20x at 540 nm, 45x at 650 nm) at ~740 nm interference layer thickness.
• Concurrent optimization of infrared absorption and visible emission.

Conclusions:

• Interference geometry significantly enhances nonlinear upconversion emission in UCNPs.
• Optimized interference layer thickness (~740 nm) provides substantial emission boosts.
• The planar design and demonstrated tolerance facilitate practical applications in photovoltaics and sensing.