Highly hydrophilic CaF2:Yb/Er upconversion nanoparticles: Structural, morphological, and optical properties

Abstract Highly hydrophilic CaF2:YbEr upconversion nanoparticles (UCNPs) were prepared by a user-friendly thermolysis route at lower temperatures. Physiochemical characteristics of the UCNPs were determined by X-ray diffraction pattern, scanning electron microscope(SEM), transmission electron microscope(TEM), energy dispersive x-ray analysis(EDX), Thermogravimetric/thermal differential analysis (TGA/DTA), zeta potential, Fourier transform infrared(FTIR), UV/Visible, UC luminescence spectroscopic techniques. XRD exhibited a highly pure, crystalline, single-phase cubic structure. SEM and TEM images revealed the irregular size, spherical-shaped, rough exterior, porous nanostructures with a typical crystalline dimension are about 10-20 nm. Zeta potential shows the positive charge over the exterior of the UCNPs and forms a highly colloidal solution at environmental temperature. FTIR spectrum illustrated the existence of carboxylic and broad hydroxyl group peaks because of the little amount of organic additive (ethylene diamine tetraacetic acid). Higher mass loss (∼5%) at a lower temperature in TGA/DTA spectrum indicates the elimination of the little amount of surface anchored organic moieties. The absorption spectrum and bandgap energy were recorded to evaluate the optical properties of the sample. UC luminescence spectrum of the sample demonstrated most of the emission transitions of Er3+-ions on irradiation sample from 980 nm laser diode. These surface hydrophilic nature UCNPs to be highly emerging photonic-based bio-related or applied materials applications.