White light upconversion through precise manipulation of energy transfer channels in a core-shell-shell nanostructure

Lanthanide-Doped KMgF3 Upconversion Nanoparticles for Photon Avalanche Luminescence with Giant Nonlinearities

“…Lanthanide (Ln 3+ )-doped upconversion nanoparticles (UCNPs) have attracted a tremendous amount of interest in a wide array of research fields because they can highly efficiently convert low-energy near-infrared (NIR) irradiation into high-energy radiation in the ultraviolet, visible, and NIR spectral regions. − Various mechanisms have been established for the upconversion luminescence (UCL) of lanthanides, including excited-state absorption (ESA), energy transfer upconversion (ETU), cooperative sensitization upconversion (CSU), energy migration upconversion (EMU), and photon avalanche (PA). − Among these mechanisms, PA is considered to be the most efficient because of the positive-feedback cycles of ESA and cross-relaxation (CR), which boost the upconversion efficiency with large nonlinearities of up to tens of orders. − PA nanoparticles hold great promise in many frontier applications such as miniaturized lasers, optical computing, super-resolution bioimaging, single-molecule tracking, and quantum optics. − However, realizing PA in colloidal Ln 3+ -doped UCNPs with giant nonlinearities remains notoriously difficult due to the serious energy loss associated with nonradiative relaxation and the surface quenching effect, − despite the fact that PA of lanthanides has been frequently reported in bulk materials and at low temperatures. − …”