Photon upconversion: Steering light with supercritical coupling

https://phys.org/news/2024-02-photon-upconversion-supercritical-coupling.html

"upconversion to higher-energy photons.... supercritical coupling addresses irradiance of lanthanide-doped nanoparticles and optical resonances' critical coupling conditions... optical bound states in continuum (BICs) traps light in open structures with theoretically infinite lifetimes... manipulating interaction between dark and bright enhances local optical field and controlled light emission direction... 8-orders magnitude increased upconversion luminescence... quantum photonics, coupled resonators, super-resolution imaging"