Combustion. synthesis and luminescence properties of nanocrystalline monoclinic SrAl2O4 : Eu2+

Nanocrystals of SrAl2O4:Eu2+ have been prepared by combustion synthesis. The results of XRD indicated that the resulting SrAl2O4:Eu2+ nanocrystals have a reduced and distorted monoclinic lattice compared with bulk materials. Both the excitation and emission spectra of SrAl2O4:Eu2+ nanocrystals shifts to higher energies in contrast to the bulk materials. The band structure calculation is performed using first-principles full potential-linearized augmented plane wave method within density functional theory. The calculated results are in reasonable agreement with our experimental results.

Facile synthesis and photoluminescent properties of redispersible CeF3, CeF3 : Tb3+, and CeF3 : Tb3+/LaF3 (core/shell) nanoparticles

CeF3, CeF3:Tb3+, and CeF3:Tb3+/LaF3 (core/shell) nanoparticles were prepared by the polyol method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), UV-vis absorption spectra, photoluminescence (PL) spectra, and lifetimes. The results of XRD indicate that the obtained CeF3, CeF3:Tb3+, and CeF3:Tb3+/LaF3 (core/shell) nanoparticles crystallized well at 200 degrees C in diethylene glycol (DEG) with a hexagonal structure. The TEM images illustrate that the CeF3 and CeF3:Tb3+ nanoparticles are spherical with a mean diameter of 7 nm. The growth of the LaF3 shell around the CeF3:Tb3+ core nanoparticles resulted in an increase of the average size (11 nm) of the nanopaticles as well as in a broadening of their size distribution. These nanocrystals can be well-dispersed in ethanol to form clear colloidal solutions. The colloidal solutions of CeF3 and CeF3:Tb3+ show the characteristic emission of Ce3+ 5d-4f (320 nm) and Tb3+ D-5(4)-F-7(J) (J = 6-3, with D-5(4)-F-7(5) green emission at 542 nm as the strongest one) transitions, respectively. The emission intensity and lifetime of the CeF3:Tb3+/LaF3 (core/shell) nanoparticles increased with respect to those of CeF3:Tb3+ core particles.

Fabrication and photoluminescence properties of core-shell structured spherical SiO2@Gd2Ti2O7 : Eu3+ phosphors

A sol-gel technique was used to prepare Gd2Ti2O7:Eu3+-coated submicron silica spheres (SiO2@Gd2Ti2O7:Eu3+). The resulted SiO2@Gd2Ti2O7:Eu3+ core-shell particles were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive x-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, as well as kinetic decays. The XRD results demonstrate that the Gd2Ti2O7:Eu3+ layers begin to crystallize on the SiO2 spheres after annealing at 800 degrees C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size similar to 620 nm), non-agglomeration, and smooth surface. The thickness of the Gd2Ti2O7:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (60 nm for four deposition cycles). Under the irradiation of 310 nm ultraviolet, the SiO2@GdTi2O7:Eu3+ samples show strong emission of Eu3+.