Primary RGB-emitting single core@quadruple-shell upconversion nanoparticle for full-color displays

The realization of primary red, green, and blue (RGB) luminescence from a single upconversion nanoparticle (UCNP) enables multicolor fine-tuning of the upconversion luminescence through the combination of RGB emissions, ultimately making it suitable for color volumetric display applications. However, excitation-wavelength-orthogonal RGB-emitting UCNPs require complex nanostructures and the synthesis of such RGB-emitting single UCNPs remains a great challenge. Here, we report a core@quadruple-shell (C@4S) single UCNP that exhibits primary tricolor upconversion luminescence under near-infrared (NIR) excitations. We first synthesize NaYbF 4 :Ho which emits green and red light under low- and high-power 980 nm NIR light. Then the NaYbF 4 :Ho core is coated with a NaYF 4 shell followed by the successive growth of NaYF 4 :Yb,Tm, NaYF 4 :Nd,Yb, and NaYF 4 shells. The synthesized NaYbF 4 :Ho@NaYF 4 @NaYF 4 :Yb,Tm@NaYF 4 :Nd,Yb@NaYF 4 C@4S UCNPs emit blue light under 800 nm excitation. By adjusting the power and wavelength of NIR light, the C@4S UCNPs exhibit various emission colors, including blue, sky-blue, green, yellow-green, orange, red, white, and more. Finally, the transparent C@4S UCNP-polydimethylsiloxane composite is prepared and various color images are displayed by simply scanning NIR light within the composite, indicating the high potential of the C@4S UCNPs for full-color display applications.