RESUMO
Eu³âº doped BaSrMg (PO4)2 were prepared by a hydrothermal method. The crystal structure and morphology of BaSrMg(PO4)2:Eu³âº phosphor were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM). The effects of different pH values (5, 6, 7 and 8) and different reaction temperatures (120, 140, 160, 180 and 200 °C) on the crystal structure and morphology of BaSrMg(PO4)2:Eu³âº phosphor were studied in this paper. The results of XRD indicate that diffraction peaks are sharp and strong only when pH value is 6, meanwhile the FESEM shows the morphology is regular-shaped. The XRD patterns show amorphous halos superimposed with several weak sharp peaks for the samples preparing under the pH values of 5, 7 and 8. It indicates that these three samples are solid solution or mixed phases, which are in accord with the results of FESEM. From the fluorescence spectra, the peaks in the excitation spectra were assigned to the transition from 7F0 to 5D4, 5L8, 5L6 and 5D2, while the peaks of emission spectra corresponding to the transition of 5D1 --> 7F1 and 5D0-->7Fj (J = 0, 1, 2, 3 and 4). The strongest emission peak of the optimized phosphor located at 613 nm (5D0--> 7F2), excited by the main excitation peak with wavelength of 394 nm. The splitting of the emission peaks changes depends on pH values and temperatures, which indicating that luminescence properties is closely related to the crystal structure and morphology of particles.
RESUMO
Surface-enhanced Raman scattering (SERS) of thiosalicylic acid (TSA) with sulfydryl group was investigated on the surface of electrochemically roughed silver electrode. The result shows that SERS enhancement effect was relative to the concentration and pH, and 1 x 10(-3) mol x L(-1) and pH 4 were the optimal condition. While the concentration increased, the enhancement effect decreased quickly because of steric hindrance. S--Ag peak position by the absorption of TSA was basically consistent, but pH significantly affected its intensity. The distribution and mechanism of TSA at different pH were further investigated. It was showed that TSA was adsorbed on the active silver surface via the sulfydryl group without H of neutral C4H4 (COOH)SH molecule. Competitive adsorption of negative valence C4H4 (COO-) SH and OH- may bring non-SERS under the strong base condition. At the same time, the sulfydryl group significantly influenced the carboxyl vibration peak's change and the distribution of electron cloud of benzene ring conjugate system.
RESUMO
A single-host white-light-emitting phosphor BaSrMg(PO4)2 : EU2+ was prepared by high temperature solid-state reaction method, and the luminescence characteristics and XRD pattern were investigated. The results showthat BaSrMg(PO4)2 phase was obtained by sintering at 1 200 degrees C for 3 hours. BaSrMg(PO4)2 = Eu2+ phosphor exhibits two main emission bands peaking at 424 and 585 nm, respectively. The emission band peaking at 424 nm is attributed to the 4f 6 5d1 --> 4f7 transition of Eu2+ substituting Sr2+, while the emission band peaking at 585 nm originates from the 4f 6 5d1 --> 4f7 transition of Eu2+ replacing Ba2+ in host lattice. The excitation spectra of the two emission peaks are range from 250 to 400 nm and both peaking at 360 nm. The effect of the proportion of Ba and Sr, and the Eu2+ doping concentration on the emission intensity were discussed in detail. Different chromaticity coordinates were obtained for each phosphor, that is, the chromaticity coordinates of the designed phosphor is tunable for the white-emitting LED or for special purpose. Quantum efficiency was also examined for the phosphors with different Eu2+ doping concentration, and concentration quenching took place obviously when Eu2+ doping concentration was lager than 6% in mole ratio. The obtained phosphor BaSrMg(PO4)2 : Eu2+ can be excited by near ultraviolet radiation effectively and emit full color lighting, which is a promising single-host white-light-emitting phosphor for white LED.