Lifetime Manipulation by Excitation Power in Lanthanide Core–Shell Nanocrystals Without Altering Composition

ABSTRACT Fluorescence lifetime extends optical multiplexing capability by exploiting the temporal dimension and offers new opportunities in optical‐based applications. However, lifetime adjustment generally relied on varying fluorophor content. We herein show that β‐NaYbF ₄ :Er@NaYbF ₄ :Nd core–shell nanocrystals exhibit an excitation power‐dependent lifetime of 1532 nm emission, making it possible to control lifetime without the necessity of altering the material. We demonstrate that a nonlinear multiphoton process accompanying with nonradiative relaxation occurs in the downshifting emission. This proposal was confirmed by perturbed‐population‐dynamics calculations and the dependence of the energy pathway on temperature and Yb ³⁺ in the sublattice. Furthermore, we demonstrate dynamic, multidimensional anti‐counterfeiting patterns using a single nanocrystal type to achieve multicolor lifetime patterns. Our work reveals a variable lifetime in unaltered nanoparticles, arising from multiphoton processes in downshifting emission, which may inspire the development of novel photonic nanomaterials for applications such as optical communication, information storage, optical sensors, and photonic computing.