VUV excitation and SEM analysis in nanofluoride produced by microwave hydrothermal synthesis

Full text: Different nanoparticles (NP's) size of barium fluoride (BaF₂) has been studied by x-ray powder diffraction (XRPD) and Rietveld refinement method analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and vacuum ultraviolet excitation measures. We show in this study that BaF₂ nanoparticles produced by hydrothermal microwave method (HTMW), displayed a structural lattice strain which depend of the NP's size. From Rietveld refinement method, were observed that lattice parameters to nanoparticles are smaller than crystal bulk. These refined lattice parameters increase as function of the median size distribution of the BaF₂ NP's. Vacuum ultraviolet excitation spectra were performed at Brazilian Synchrotron Light laboratory (LNLS) in the Toroidal grating monochromator (TGM) beamline for all samples, and was possible observe a distinct initial and final region energy to self-trapped exciton (STE) formation energy around 9.4-9.6 eV. The width band gap was observed in 10.5 eV to all samples, without shift. These results suggest that the binding energy of the self-trapped exciton depends on particle size and that the lattice strain can be induced by lattice compression as function of the nanoparticle size effect. (author)