Microsphere Photonic Superlens for a Highly Emissive Flexible Upconversion-Nanoparticle-Embedded Film

Area of Science:

• Materials Science
• Optics
• Nanotechnology

Background:

• Upconversion luminescence (UCL) efficiency is limited by intrinsic low conversion rates.
• Photonic nanostructures enhance UCL but are sensitive to environmental conditions.
• Flexible applications require robust and tunable UCL enhancement methods.

Purpose of the Study:

• To achieve giant UCL enhancement using a flexible UCNP-embedded film coupled with a microsphere photonic superlens (MPS).
• To investigate the enhancement mechanisms and validate the suppression of nonradiative transitions and thermal quenching.
• To demonstrate the potential for flexible optoelectrical devices.

Main Methods:

• Fabrication of UCNP-embedded films coupled with MPS.
• Characterization of UCL enhancement under 808 nm excitation.
• Analysis of enhancement pathways including Mie-resonant nanofocusing, whispering-gallery modes (WGMs), and antenna effects.
• Experimental validation of suppressed nonradiative transitions and thermal quenching.

Main Results:

• Achieved over 10⁴-fold UCL enhancement ratio with MPS under low excitation power (0.72 mW).
• Demonstrated enhancement via Mie-resonant nanofocusing, WGMs, and antenna effects.
• Improved UCL quantum yield by 3-fold to 4.20% under near-infrared excitation.
• Validated suppression of phonon-induced nonradiative transition and thermal quenching through optical resonance.

Conclusions:

• MPS enables giant UCL enhancement and improved quantum yield through multiple optical resonance effects.
• The flexible MPS system offers robust optical regulation for diverse applications.
• This technology opens new avenues for wearable optoelectrical devices in nanoimaging, biosensing, and energy conversion.