Full-color tuning in multi-layer core-shell nanoparticles from single-wavelength excitation

Lanthanide-based luminescent materials have shown great capabilities in addressing scientific problems encountered in diverse fields. However, achieving full-color switchable output under single-wavelength irradiation has remained a daunting challenge. Here we report a conceptual model to realize this aim by the temporal control of full upconversion evolution in a multi-layer core-shell nanostructure upon a single commercial 980-nm laser, instead of two or more excitation wavelengths as reported previously. We show that it is able to realize the red-to-green color change (from Er³⁺) under non-steady state excitation by constructing the cooperative modulation effect in the Er-Tm-Yb triple system, and single out the blue light (from Tm³⁺) by filtering out the short-decay emissions via a time-gating technique. The key role of Tm³⁺ in manipulating up-transition dynamics of Er³⁺ is further demonstrated. Our results present a deep insight into the photophysics of lanthanides, and help develop new generation of smart luminescent materials toward emerging photonic applications.