Design of host lattice for new phosphors with enhanced thermal stability via crystal structure refinement

Abstract

The present work involves design of host lattice for new phosphors with enhanced thermal stability via crystal structure refinement. In this thesis, the development of new phosphors and their analyses on the thermal stability after the baking process, which is to burn-out binder for phosphor layer on plasma display panel (PDP) bottom plate, were done using a various phosphor systems. Through current works, we suggested new crystal-related-parameters in terms of their effects on the thermal stability and it can be used as criteria for host lattice selection having a strong thermal stability. Furthermore, it is expected that these parameters will also be applicable to other samples having weak thermal resistance so as to broaden device application possibilities. Chapter III deals with development of new blue-emitting phosphors for PDP application, $CaMgSi_2O_6:Eu^{2+} (CMS:Eu^{2+})$ and $CaAl_2Si_2O_8:Eu^{2+} (CAS:Eu^{2+})$. In chapter III-1, we have optimized synthesis conditions of blue-emitting $CMS:Eu^{2+}$ with conventional solid-state reaction and successfully determined structure parameters by Rietveld refinement method with neutron powder diffraction data. The final weighted R-factor, $R_{wp}$, was 6.42 % and the goodness-of-fit indicator, S (= $R_{wp} /R_e$), was 1.34. The refined lattice parameters of $CMS:Eu^{2+}$ were a = 9.7472(3) $\AA$;, b = 8.9394(2) $\AA$; and c = 5.2484(1) $\AA$;. The β angle was 105.87(1) °. The concentration quenching process was observed and the critical quenching concentration of $Eu^{2+}$ in $CMS:Eu^{2+}$ was about 0.01 mol and critical transfer distance was calculated as 12 $\AA$;. With a help of the Rietveld refinement and Dexter theory, the critical transfer distance was also calculated as 27 $\AA$;. In addition, the dominant multipolar interaction of $CMS:Eu^{2+}$ was investigated from the relationship between the emission intensity per activator concentration and activator concentration. The dipole-dipole interaction...