Photoluminescent neodymium-doped ZnO nanocrystals prepared by laser ablation in solution for NIR-II fluorescence bioimaging.

The work reports on the use of laser ablation and post-ablation irradiation techniques for the preparation Nd doped ZnO nanoparticles (NPs). The focus has been made on photoluminescence of Nd-doped ZnO NPs in the second near infrared (NIR-II) spectral window (1000-1700 nm) of the biological transparency. Morphology, phase composition and optical properties of the synthesized NPs were studied by absorption and photoluminescence spectroscopy, X-Ray diffraction (XRD) and transmission (TEM) electron microscopy. Near-infrared luminescence of Nd doped ZnO nanocrystals in the region of 1000-1400 nm was detected both upon excitation from the ground state (800 nm) and upon UV excitation. The latter proves the incorporation of the Nd into ZnO lattice as photoluminescence occurs through the transfer of excitation energy from the ZnO matrix to the Nd ion. The possibility of control over the luminescence properties by a variation of solvent composition and by additional laser irradiation was demonstrated.