Upconversion Nanoprobes: Recent Advances in Sensing Applications.

Abstract

Rare earth ions doped upconversion nanoparticles (UCNPs) are capable of stepwisely converting two or more lower energy near-infrared (NIR) excitation photons into a higher energy visible and ultraviolet emission photon, resulting in a large anti-Stokes shift of several hundred nanometers. Because the f-electron configurations of lanthanide ions have abundant energy levels, and many of them possess long lifetimes, UCNPs exhibit unique optical properties including optical tunability over emission wavelengths and lifetimes, better photo-stability and improved monochromatic color-purity and spatial resolution. However, the low luminescent efficiency, largely owing to their substantially weak and narrow band absorptions, has greatly hampered the translation of UCNPs-based technologies from the academic stage to real world products. Recently, increasing efforts have been paid on boosting the upconversion luminescence brightness and efficiency, including inert shells coating, high concentration of activators dop...