Mechanistic Investigation of Photon Upconversion in\nNd³⁺-Sensitized Core–Shell Nanoparticles

Abstract

A new\ntype of core–shell upconversion nanoparticles which\ncan be effectively excited at 795 nm has been designed and synthesized\nthrough spatially confined doping of neodymium (Nd³⁺) ions.\nThe use of Nd³⁺ ions as sensitizers facilitates the energy\ntransfer and photon upconversion of a series of lanthanide activators\n(Er³⁺, Tm³⁺, and Ho³⁺) at a biocompatible\nexcitation wavelength (795 nm) and also significantly minimizes the\noverheating problem associated with conventional 980 nm excitation.\nImportantly, the core–shell design enabled high-concentration\ndoping of Nd³⁺ (∼20 mol %) in the shell layer and\nthus markedly enhanced the upconversion emission from the activators,\nproviding highly attractive luminescent biomarkers for bioimaging\nwithout autofluorescence and concern of overheating.