Independent Luminescent Lifetime and Intensity Tuning of Upconversion Nanoparticles by Gradient Doping for Multiplexed Encoding.

Luminescent materials with engineered optical properties have been developed for multiplexed labeling detection, where encoding capacity plays a pivotal role in the efficiency. However, multi-dimensional optical identities are usually not independent which essentially hinder the practical encoding numbers to access theoretical capacity. In this work, we carefully studied the sensitizer gradient doping structure in near-infrared (NIR) excitable upconversion nanoparticles (UCNPs) and managed to achieve independent emission intensity and lifetime tuning. With the orthogonally tunability, it breaks the constraint of intensity (k) and lifetime (n) correlation and expands the practical encoding number to theoretical value as (k+1)n -1 in binary encoding. This method can also be combined with previous lifetime engineering as well to realize high level multiplexing.