KCS

Upconversion nanoparticles (UCNPs) can convert near-infrared (NIR) light into visible emissions by sequentially absorbing multiple photons. The facile synthesis of Yb³⁺/Er³⁺-doped NaLuGdF₄ nanoparticles coated with polyethyleneimine (PEI) and polyacrylic acid (PAA) was accomplished by the one-step hydrothermal method. The UCNPs capped with the functional groups (-COOH and -NH2) of PEI/PAA on the surface make the UCNPs water soluble and nontoxic for bioapplications. The visible green and red emissions are observed from the UCNPs upon NIR excitation. The characterizations of NaLuGdF₄:Yb³⁺/Er³⁺ were performed by using photoluminescence (PL), field emission scanning electron microscope (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The FT-IR spectra were measured to confirm the successful capping of PEI/PAA ligands on the surface of UCNPs. It was revealed tht the nanoparticles were spherical with a uniform size of 50-60 nm in FE-SEM images. In addition, these high-quality UCNPs have prominent potential applications for optical nanodevices, bioimaging, and bioanalytic sensing.