Fig. 2: Fundamental characterizations of LIBRA.
Transmission electron microscopy (TEM) images of a NaErF4:Yb (Core-LnNP), b NaErF4:Yb@NaYF4:Yb (LIBRA). TEM images in (a) and (b) represent the similar results of synthesis experiments repeated independently for three times. c Scanning transmission electron microscopy (STEM) image of LIBRA. STEM image represents the similar results of synthesis experiments repeated independently for three times. High-resolution TEM (HR-TEM) images of d Core-LnNP and e LIBRA nanoparticle. The lattice planes of (1 0 0) with 0.52 nm interplanar spacing of hexagonal NaErF4 is identified in (d) and (e). HR-TEM images in (d) and (e) represent the similar results of synthesis experiments repeated independently for three times. f Energy dispersive X-ray spectroscopy (EDS) elemental mapping of LIBRA, showing the distributions of Er (blue dots), Yb (yellow dots), and Y (red dots) elements in the core and shell layers of the nanocomposite. EDS elemental mapping image represents the similar results of synthesis experiments repeated independently for three times. g Representative EDS line scan analysis of LIBRA. Inset, STEM image of the nanoparticle performed with EDS line scan. EDS line scan and STEM results represent the similar outcomes of synthesis experiments repeated independently for three times. h Fourier transform infrared (FTIR) spectra of the as-synthesized LIBRA capped with oleic acid (CSLnNP-OA) and after 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-poly(ethylene glycol) (DSPE-PEG) modification (LIBRA@PEG). i Near-infrared (NIR) luminescence spectra of Core-LnNP and LIBRA modified with DSPE-PEG in aqueous solutions. The protection effect of NaYF4:Yb shell layer results in a nearly 23-fold enhancement of NIR emissions in LIBRA@PEG compared to Core-LnNP.
