Enhanced single-band red upconversion luminescence of α-NaErF4:Mn nanoparticles by a novel hollow-shell structure under multiple wavelength excitation

Abstract

Upconversion nanoparticles (UCNPs) doped with lanthanide ions have potential applications in biomedical, solar cells and displays. However, the intensity of the upconversion luminescence (UCL) is limited by the surface effects of nanomaterials, lattice defects, etc. Here, a novel α-NaErF4 hollow nanocube is fabricated by using divalent manganese ions (Mn2+) to substitute trivalent erbium ions (Er3+) in the NaErF4 matrix. The hollow-shell structure can weaken the luminescence quenching and surface quenching effects, reduce the energy loss of higher energy levels in nanoparticles, and improve the light capture ability of nanoparticles. So the UCL of α-NaErF4 hollow nanocubes is greatly improved, which is 14, 790 and 1071 times higher than that of the β-NaErF4 under 808, 980 and 1530 nm laser excitation, respectively, and the emission in the red region is enhanced respectively by 69, 2049 and 2902 times. In particular, the hollow nanocubes emit intense single-band red emission under the three different wavelengths, respectively. Moreover, the magnetization of α-NaErF4 hollow nanocubes is 2.16 emu g−1 at room temperature, which is larger than that of gadolinium-based materials. Hollow-shell structure, excellent paramagnetism and single-band red upconversion emission excited by various wavelengths will create NaErF4:40Mn UCNPs a good application prospect in the biomedical field.