Investigation of the spectra of Sr2CeO4 due to charge transfer transition

Abstract

Sr2CeO4 and Ca2+/Ba2+ doped Sr2 CeO4 samples with two different formation mechanisms were prepared by a solid-state method and their luminescent properties were investigated. For the Sr2CeO4(Ⅰ) sam ples formed by the direct reaction between SrO and CeO2, the peak of the strong excitat ion band appeared at about 256 nm while that for the Sr2CeO4(Ⅱ) sa mples obtained by the reaction between SrCeO3 and SrO was observed at about 279nm. It w as found that the solubility of Ca2+ in Sr2CeO4(Ⅱ) w as very low while Ca2+ could replace part of Sr2+ in Sr2CeO 4(Ⅰ). The substitution of Sr2+ by Ca2+ in Sr2CeO4(Ⅰ) led to r ed shift of the strong excitation band and its spectral shape approached that of Sr2CeO4(Ⅱ) with the in crease of Ca2+. The strong excitation band was attributed to the char ge tr ansfer transition of the terminal Ce4+—O2- bonds of CeO6 octahedr a. The peak of the weak excitation band located at about 340nm remained unchange d in all the samples, however, its intensity was found to increase with red shif t of the strong excitation band. This band might originate from the charge trans fer transition of the equatorial Ce4+—O2- bonds of CeO6 octahedra . The formation mechanism and the doping of Ca2+ had no effect on the emission spectra. Ba2+ was not incorporated in the Sr2CeO 4 phase in any formation mechanism and it only produced a second crystalline phase of BaCeO3.