| 研究概要 |
In this year, synthesis and characterization of novel water soluble phosphate ester and confirmation of their advantages by synthesis of a LiCaPO_4 : Eu^2+ phosphor were conducted. A stable and water soluble-phosphate ester was synthesized from reaction among polyethylene glycol 300, P_2O_5, and Polyphosphoric acid. Polyphosphoric acid, polyethylene glycol 300, and P_2O_5 were mixed in N_2 atmosphere. ^<31>P{^1H}NMR spectra of the prepared phosphate oligomers were recorded. The proportion of phosphoric acid and phosphate ester was depended on the reflux condition. The amount of H_3PO_4 was around 12%, while around 45% H_3PO_4 was unreacted using the previous method.
Eu-doped LiCa_<097> PO_4:0.03Eu^<2+> was synthesized by the polymerizable complex (PC) method employing a prepared phosphate ester. In addition, the synthesis by the SSR method was conducted. Excitation and emission spectra of phosphors were compared. The strongest emission intensity among three samples was observed at the sample synthesized by PC method employing phosphate ester. PC method using phosphate ester could produce homogeneous Eu distribution. Therefore, the sample prepared by PC method employing phosphate ester showed the highest emission intensity. Finally, development of the phosphate source to use for solution based method was successfully conducted and the advantage of phosphate ester was proved by synthesis of LiCaPO_4 : Eu^2+ phosphor.
Using the developed PC method, we synthesized NaBa_<1-x>Ca_xPO_4 solid solutions via PC method, and investigated their photoluminescence properties and crystal structures. As increase of Ca substitution, emission intensity decreased and the red shift of emission center was observed from 438 nm to 455 nm under excitation at 320 nm. XRD measurements of the samples revealed that NaBa_<0.5>Ca_<0.5>PO_4 at x = 0.5 and Na_3Ba_2CaPO_4 at x = 1/3 were solid solutions of them. Finally, we found two kinds of new compositions and determined their crystal structures.
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