Significantly enhanced luminescence of dual wavelength excitation upconversion nanoparticles by two-dimensional technique

In this work, the monodisperse NaGdF 4 @ NaGdF 4 :Yb/Er @ NaGdF 4 :Yb/Nd nanoparticles have been prepared via a modified solvothermal method . Under the 808 nm or 980 nm excitation, a bright upconversion luminescence （UCL）of the inert-core/luminescent-shell/active-shell nanoparticles can be both observed. Importantly, the intensity of luminescence is up to around 25-fold that of NaGdF 4 :Yb/Er @ NaGdF 4 :Yb/Nd core-shell nanoparticles under 808 nm excitation, which is more advantageous in biological application. This is because, compared with the traditional core-shell structure, the two-dimensional doping (inert-core/luminescent-shell/active-shell) design not only reduces the distance between Yb 3+ and Er 3+ ions, but also further reduces the energy loss by physically separating Er 3+ from the nuclei with a large number of defects, which are both conducive to the improvement of energy transfer efficiency. This research will provide important reference value for the development of high-performance up-conversion nanomaterials .