Self-assembled conjugated polymer spheres as fluorescent microresonators

Area of Science:

• Materials Science
• Optics and Photonics
• Polymer Chemistry

Background:

• Light confinement in active medium cavities amplifies emission.
• Whispering gallery modes (WGMs) effectively amplify light via total internal reflection in high-refractive-index microstructures.
• WGMs involve light propagating along the circumference of a sphere.

Purpose of the Study:

• To investigate whispering gallery mode (WGM) photoemission in π-conjugated polymer microspheres.
• To explore the relationship between microsphere properties and WGM emission characteristics.
• To assess the technological potential of these polymer microspheres.

Main Methods:

• Fabrication of isolated single microspheres (2-10 μm diameter) from self-assembled π-conjugated alternating copolymers.
• Laser pumping to induce photoemission.
• Analysis of emission peak wavelengths, Q-factor, and their dependence on sphere size, excitation spot position, and polymer refractive index.

Main Results:

• Demonstrated WGM photoemission from π-conjugated polymer microspheres.
• Emission peak wavelengths were sensitive to sphere size, excitation spot position, and polymer refractive index.
• The Q-factor increased with sphere diameter, showing a linear correlation with reciprocal radius, suggesting improved total internal reflection efficacy with larger spheres.

Conclusions:

• WGM photoemission in π-conjugated polymer microspheres is a novel phenomenon.
• These microspheres act simultaneously as fluorophores, high-refractive-index media, and resonators.
• The simple fabrication and multifunctional nature suggest high technological impact for applications in photonics and optoelectronics.