Light Management in Upconverting Nanoparticles: Ultrasmall Core/Shell Architectures to Tune the Emission Color

Ultrasmall NaGdF4 nanoparticles with core/shell and core/shell/shell architectures have been synthesized following a microwave-based thermolysis procedure, allowing us to rapidly obtain homogeneous nanoparticles compared to,conventional heating. To analyze the possibilities of the, proposed structure in terms of tuning the emission color, core and shells have been doped with different lanthanide ion pairs (either Er3+/Yb-3+ and/or Tm3+/Yb3+), keeping them, therefore spatially separated inside the different layers of the nanoparticles. Here, we demonstrate that the position of the dopants inside the nanoparticles affects the intensity of the different emission bands of the luminescing TM3+ and Er3+ ions show how it has a relevant effect on the overall emission color of the luminescence obtained after 975 nm excitation.