Electrospun Nd³⁺-doped spinel nanoparticles/nanofibers with both excitation and emission wavelengths in the optical window of cells and tissues

ZnAl₂O₄ nanofibers and nanoparticles were in situ synthesized by electrospinning technique. Utilizing poly (vinyl pyrrolidone) (PVP) with different degree of polymerization, SEM (scanning electron microscope) results indicate that ZnAl₂O₄ nanostructures exhibit different morphologies under the same electrospun parameters. When PVP with high molecular weight (Mw = 1,300,000) was used, the ultra-long ZnAl₂O₄ nanofibers were obtained with an average diameter of ∼200 nm. However, while PVP with low molecular weight (K-30) was used, the ZnAl₂O₄ changed into particle-shape with an average size of ∼100 nm. Utilizing Nd³⁺ ions as the optical activator, three emission peaks centered at 905 nm, 1064 nm and 1335 nm were detected respectively in the photoluminescence (PL) spectra of ZnAl₂O₄:Nd³⁺ nanostructures under 808 nm laser excitation. It is noticed that both the excitation wavelength (808 nm) and the emission wavelength (905 nm and 1064 nm) are located in the 700–1100 nm optical window of cells and tissues. And the cytotoxicity investigation indicates ZnAl₂O₄:Nd³⁺ nanostructures are biocompatible with human cells, which endow their potential application as biological mark-ers, etc.