Study On The Solid State Reaction Mechanism Of SrO-CeO₂ System And The Spectral Properties

The solid state reaction process of the mixture of SrC0₃ and CeO₂ powders with different Sr/Ce ratios was studied by use of XRD and TG/DTA method. The results showed that SrCeO₃ and Sr₂Ce0₄ phases were developed in the initial stages of the reaction above 950°C and only Sr₂Ce0₄ phase was developed at a lower temperature. There were two types of formation mechanism respectively for SrCeO₃ and Sr₂Ce0₄. When the firing temperature was above 1000°C, SrO and CeO₂ converted directly to SrCeO₃, and Sr₂Ce0₄ was formed by the reaction between SrCeO₃ and SrO. However, SrO and CeO₂ converted directly to Sr₂Ce0₄ below 950°C, and SrCe0₃ was formed by the reaction between Sr₂Ce0₄ and CeO₂ at about 950°C. On the basis of results, phase composition of SrO- CeO₂ system was given, and some wrong results in certain papers had been clarified. Sr₂Ce0₄ phosphor was synthesized by mechanical milling and reactive sintering. The solid state reaction of SrC0₃ and Ce0₂ (2:1) started at 850°C, and completed at 1200°C for about 2h.Sr₂Ce0₄ and Ca²⁺/Ba²⁺doped Sr₂Ce0₄ samples with two different formation mechanisms were prepared by a solid-state method and their luminescent properties were investigated. For the Sr₂Ce0₄(I) samples formed by the direct reaction between SrO and CeO₂ , the peak of the strong excitation band appeared at about 256 nm while that for the Sr₂Ce0₄(II) samples obtained by the reaction between SrCeO₃ and SrO was observed at about 279 nm. It was found that the solubility of Ca²⁺ in Sr₂Ce0₄ (II) was very low while Ca²⁺ could replace part of Sr²⁺ in Sr₂Ce0₄ (I). The substitution of Sr²⁺ by Ca²⁺ in Sr₂Ce0₄ (I) led to red shift of the strong excitation band and its spectral shape approached that of Sr₂Ce0₄(II) with the increase of Ca²⁺. The strong excitation band was attributed to the charge transfer transition of the terminal Ce⁴⁺—0^2- bonds of CeO₆ octahedra. The peak of the weak excitation band located at about 340nm remained unchanged in all the samples, however, its intensity was found to increase with red shift of the strong excitation band. This band might originate from the charge transfer 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 Sr2Ce04 phase in any formation mechanism and it only produced a second crystalline phase of BaCeO:i.A new europium strontium oxide was synthesized by high-temperature solid state reaction of SrC03 and Eu20:) in air. The new multiple oxide was characterized by use of XRD, TG/DTA and fluorescence spectra. The XRD results showed that the molecular formula of the europium strontium oxide was SrEu2(X The excitation spectrum of SrEu2O4 displayed a broad double peaks band with one around 257nm and the other around 280nm. This broad band was attributed to the charge transfer transition of Eui+—02 bonds. Excited with a radiation of 280nm, SrEu2O4 emitted strong red light which was assigned to the 5D0-^7F2 electric dipole transition of Eu .