Morphology and size study of (Gd,Er,Yb)-doped NaYF₄ nanoparticles through the X-ray line profile analysis

Full text: X-ray line profile analysis (XLPA), i.e. the analysis of the broadening, shifting and asymmetries of the Bragg reflections due to microstructure, enables the thorough characterization of the properties of materials, especially those of nanostructured materials. XLPA makes a quantitative analysis of the microstructure in terms of grain and subgrain size, dislocation structure and dislocation densities and planar defects, especially stacking faults and twin boundaries. In this work, we use the XLPA to determine the shape and size of the system of nanoparticles (NPs) Gd-, Er- and Yb-doped NaYF₄. For Yb/Er and Yb/Tm co-doped NaYF₄ samples, the up converting fluorescence effect has been observed. It is known that in nanosystems both size and shape of the particles can change the physical properties. In particular, the title samples crystallize in both hexagonal (h) and cubic (c) symmetries depending on the dopant and heat treatment [2,3]. The powder diffraction data were collected at the XPD beamline of the Brazilian synchrotron light source. For the deconvolution of the instrumental contribution, standard samples of LaB6-NIST were used. The analysis was carried out by using the convolutional multiple whole profile (CMWP) fitting procedures. To obtain the mean size of crystallites and/or their size-distributions, specific functional form of size-distribution has to be assumed. The log-normal size distribution function has been used to describe the size profile of our samples. For h NPs, size distribution of about 400 nm were obtained, while less than 100 nm were observed for c Nps, depending on the heat treatment. This is in agreement with TEM and HRTEM results. Our results are correlated with the optical and magnetic properties observed. (author)