Enhancement of luminescence properties of a KSrPO₄:Eu ²⁺ phosphor prepared using a solution method with a water-soluble phosphate oligomer

A novel phosphate raw material having an oligomeric structure with desirable stability and solubility under aqueous conditions was prepared via an esterification reaction between H₃PO₄ and ethylene glycol under reflux. A blue emitting KSrPO₄:Eu²⁺ phosphor with high luminescence was subsequently synthesized using a polymerizable complex (PC) method with the prepared phosphate oligomers as a source of P. KSrPO ₄:Eu²⁺ thus prepared exhibited higher emission intensity than samples prepared using a solid state reaction method or the PC method using H₃PO₄. This high luminescence was attributed to the excellent homogeneity of the constituents in the sample. It was found that KSrPO₄ doped with more than 3 mol% of Eu²⁺ showed a new low-energy emission band at approximately 480 nm, in addition to the known emission band at 428 nm. This new feature was speculated to be derived from disordering of K and Sr ions caused by the high homogeneity of the constituents. Moreover, it was confirmed that thermal quenching of emission at 428 nm above 423 K was recovered in samples doped with more than 7% of Eu.