Ying Li

Aluminum-substituted mesoporous SBA-15 (Al−SBA-15) materials were directly synthesized by a hydrolysis-controlled approach in which the hydrolysis of the silicon precursor (tetraethyl orthosilicate, TEOS) is accelerated by fluoride or by using tetramethyl orthosilicate (TMOS) as silicon precursor rather than TEOS. These materials were characterized by powder X-ray diffraction (XRD), N2 sorption isotherms, TEM, 27Al MAS NMR, IR spectra of pyridine adsorption, and NH3-TPD. It is found that the matched hydrolysis and condensation rates of silicon and aluminum precursors are important factors to achieve highly ordered mesoporous materials. 27Al MAS NMR spectra of Al−SBA-15 show that all aluminum species were incorporated into the silica framework for the samples prepared with the addition of fluoride. A two-step approach (sol−gel reaction at low pH followed by crystallization at high pH) was also employed for the synthesis of Al−SBA-15. Studies show that the two-step approach could efficiently avoid the leaching of aluminum from the framework of the material. The calcined Al−SBA-15 materials show highly ordered hexagonal mesostructure and have both Brönsted and Lewis acid sites with medium acidity.

Ba1.8–xSrxSiO4:0.1Ce3+,0.1Na+ (x = 0–1.8) phosphors were prepared by a high-temperature solid-state reaction. The emission peaks of Ba1.8–xSrxSiO4:0.1Ce3+,0.1Na+ shift from 391 to 411 nm with increasing Sr2+ content under excitation by a UV light at around 360 nm. Ba0.4Sr1.4SiO4:0.1Ce3+,0.1Na+ phosphor exhibits the best performance of luminescence, whose absolute quantum efficiency is 97.2%, and the emission intensity at 150 °C remains 90% of that at room temperature. The effect of replacing Ba2+ by Sr2+ on the red shift of the emission band and the increase of quantum efficiency (QE) and thermal stability (TS) was investigated in detail based on the Rietveld refinements, Raman spectra, thermoluminescence, and decay curves, etc. The performance of UV chip-based pc-LEDs indicates that Ba0.4Sr1.4SiO4:0.1Ce3+,0.1Na+ can be a promising blue phosphor for white-emitting pc-LEDs.