RESUMO
The Ca9.95-x Na0.75 K0.25 (PO4)7: Eu.0.05(2+), Mn(x)2+ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7) phosphors were synthesized by high temperature solid-state reaction, and their phase composition and fluorescence emission properties were studied. Due to the existence of double phases with similar crystal structure, the 5d-4f transition of Eu2+ ions in the phosphors emits a fluorescence of wide wavelength with peaks located at 491 nm and 540 nm respectively. The energy transfer between Eu2+ and Mn2+, together with the occupation of Mn2+ ions at the eight coordination sites in the phosphors, makes the 4T1 (4G)-6A1 (6S) transition of Mn2+ ions eimit red emission peaked at 635 nm. The combination of fluorescence emtted by Mn2+ and Eu2+ ions results in the emission of white light with color coordinates (0.3335, 0.2924), (0.3999, 0.3179) and (0.3307, 0.2564). The nearly pure white light emitting makes the phosphors show great application potential in the white light-emitting LEDs.
RESUMO
We demonstrate the switching of light in the near-infrared region (1.55 microm) through the manipulation of magnetic nanoparticles in a magnetic fluid by using another light in the visible region (0.532 microm). The formation of a photonic gap is found in the magnetic fluid when a laser light or a magnetic field is applied. A shift of the photonic gap to longer wavelengths is observed with increasing laser power or magnetic field strength.
RESUMO
The Ba1.97 Ca1-x (B3O6)2 : Eu2+, Mn(x)2+ (x = 0, 0.03, 0.06, 0.15) phosphors were synthesized by high temperature solid-state reaction, and their phase composition and luminescence properties were studied. In these phosphors, Eu2+ locates at the crystal sites of Ba2+ and Ca2+ ions. Under 317 nm UV light excitation, the 5d --> 4f transition of Eu2+ forms a broad blue emission band with a peak at 450 nm. With the energy transfer from Eu2+ ions, Mn2+ ions emit a broad red band with the peak at 600 nm. The mixture of the broad blue emission and a broad red emission forms an approximate white light with the CIE chromaticity (x = 0.371, y = 0.282). The phosphors can be excited effectively by UV light in the range of 250-400 nm, so they are the potential candidates for single white light-emitting phosphor excited by UV-LED.
RESUMO
Eu3+ -doped MCeO3 (M==Sr, Ba) powder samples were prepared by a solid-state method, and their characteristics were investigated by the use of XRD an d fluorescence spectra. The XRD results show that Eu3+ ions hav e a preferencefor M2+ over Ce4+ sites in MCeO3 (M==Sr, Ba) lattice. The excitation spectra of SrCeO3:Eu3+ and BaCeO3:Eu3+ display a much broad absorption band peaking at about 311 nm and 320 nm, respectively. This broad band is attributed to the charge transfer from O0- to Ce4+ and the energy transfer from SrCeO3 and BaCeO3 to Eu3+. In the MCeO3:Eu3+ samples, the emission transitions of Eu3+ originating from (5)D1 and (5)D0 excited states can be observed, among which the (5)D0--(7)F1 magnetic-dipole transition is the most intense emission. The emission of Eu3+ from the Eu3+ doped SrCeO3 lattice is much stronger than that of Eu3+ from the Eu3+ doped BaCeO3 lattice.
RESUMO
A new europium strontium oxide was synthesized by high-temperature solid state reaction of SrCO3 with Eu2O3 in air. The new multiple oxide was characterized by use of XRD, TG/DTA and fluorescence spectra. The XRD results show that the molecular formula of the europium strontium oxide is SrEu2O4, whose structure is isostructural with that of BaEu2O4 reported earlier. The excitation spectrum of SrEu2O4 displays a broad double peaks band with one peak around 257 nm and the other around 280 nm. This broad band is attributed to the charge transfer transition of Eu3+-O2- bonds. Excited with a radiation of 280 nm, SrEu2O4 emits strong red light which is assigned to the 5D0-->7F2 electric dipole transition of Eu3+.
RESUMO
The phase composition of SrCO3 and CeO2 (2:1) powder mixture calcined at different temperatures was identified by X-ray diffraction method. It was found that there were two types of formation mechanism of Sr2CeO4. When the starting powder mixture was fired above 1000 degrees C, the unstable intermediate phase SrCeO3 developed, which then reacted with SrCO3 to form the final product Sr2CeO4, however when the sintering temperature was lower, SrCO3 and CeO2 were converted directly to Sr2CeO4. The excitation spectra of Sr2CeO4 were quite different for different formation mechanism. The strong excitation band presented maxima at about 280 nm for the samples formed by the former mechanism, while the maxima were at about 254 nm for the samples formed by the latter mechanism. The formation mechanism had no effect on the emission spectra.