Low-temperature synthesis of SrAl 2O 4 by a modified sol–gel route: XRD and Raman characterization

Abstract

Among other alkaline-earth aluminates, the monoclinic (M) polymorph of SrAl 2O 4 can be used as host material for Eu 2+ luminescence based phosphors. With the aim of reducing the synthesis temperature of this polymorph, we have produced and characterized by XRD and Raman scattering solid solutions of the SrAl 2− x B x O 4 system ( x ⩽ 0.3 ) obtained by two different methods, a ceramic route and a modified sol–gel synthesis. Though the addition of boron lowers the temperature of obtention of the M polymorph in both type of samples, lower B contents are needed to stabilize the M form as single phase for samples prepared by the sol–gel method than through the ceramic route. In the sol–gel method, the M polymorph can be obtained at temperatures as low as 1200 °C, with a Boron content of just 1%. Rietveld profile analysis allows us to conclude that coexistence of the monoclinic and hexagonal polymorphs of SrAl 2O 4 occurs for samples synthesized below an onset temperature of about 1000–1100 °C, that depends on the sample composition. Above those temperatures, only the monoclinic phase is formed.