RESUMO
We report the surface modification of nanocrystalline Gd2O3:Eu(3+) phosphor by (3-Aminopropyl)trimethoxysilane (APTMS). The nanoparticles were first coated with silica using the Stöber process, and then annealed at 650 °C for 2 h. Afterwards, APTMS was functionalized onto the silica layer to obtain Gd2O3:Eu(3+) nanoparticles bearing amine groups on the surface. The effect of silica coating, and the subsequent annealing process on the crystallization of the nanophosphor were analyzed by x-ray diffraction (XRD). High-resolution transmission electron microscopy (HR-TEM) confirmed the presence of a silica layer of â¼45 nm thickness. X-ray photoelectron (XPS) and Fourier transform infrared (FTIR) spectroscopy confirmed the presence of silica and the amine groups. Photoluminescence (PL) analysis demonstrated an increased emission after functionalization of nanoparticles. Absolute quantum yield (QY) measurements revealed an 18% enhancement in QY in functionalized nanoparticles compared with unmodified nanoparticles, which is of great importance for their biomedical applications.
RESUMO
New red luminescent powders of La(1-x)Pr(x)Sr2AlO5 (x = 0.01 at.) were prepared by the combustion synthesis method. Microstructural properties were characterized by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The La(1-x)Pr(x)Sr2AlO5 X-ray diffraction pattern revealed a tetragonal phase. Morphology of the grains showed nanobars with sizes of approximately 550 nm in length. Photoluminescence, cathodoluminescence and diffuse reflectance were analyzed in detail. Photoluminescence revealed two narrow emission peaks located at lambda(em1) = 497 nm (green) and lambda(em2) = 620 nm and a single maximum excitation peak of lambda(ex) = 287 nm. The cathodoluminescence spectrum confirmed the peaks detected by photoluminescence analysis. The absorbance spectrum showed broad absorption with a maximum around lambda = 280 nm, which agrees with the maximum excitation peak detected by photoluminescence.