Nanoparticle

Metallurgy

Materials science

Photon upconversion

Photon

Physics

Nanotechnology

Optics

Doping

Nanomaterials

Rare earth

Optoelectronics

Advanced Science

Upconversion is a nonlinear optical phenomenon that involves the emission of high-energy photons by sequential absorption of two or more low-energy excitation photons. Due to their excellent physiochemical properties such as deep penetration depth, little damage to samples, and high chemical stability, upconversion nanoparticles (UCNPs) are extensively applied in bioimaging, biosensing, theranostic, and photochemical reactions. Here, recent achievements in the synthesis, optimization, and applications of UCNP-based nanomaterials are reviewed. The state-of-the-art approaches to synthesize UCNPs in the past few years are introduced first, followed by a summary of several strategies to optimize upconversion emissive properties and various applications of UCNPs. Lastly, the challenges and future perspectives of UCNPs are provided as a conclusion.

Recent Progress of Rare‐Earth Doped Upconversion Nanoparticles: Synthesis, Optimization, and Applications