Effects of defects on the quantum efficiency of Eu2+ -doped aluminates with the magnetoplumbite-type crystal structure

The luminescence of SrAl₁₂O₁₉ : Eu²⁺ phosphors can be quenched by substitution of a small amount of Mg for Al, or by preparing samples with excess Al₂O₃. It is most probable that oxygen vacancies near the Eu²⁺ activator ions act as the radiationless sinks of the excitation energy. In CaAl₁₂O₁₉ : Eu²⁺ the quenching of the luminescence by the introduction of defects is much less effective, so that less oxygen vacancies are supposed to be formed. In view of the fact that the stability of CaAl₁₂O₁₉, with respect to less oxygen containing phases, is higher than that of SrAl₁₂O₁₉, this is a reasonable assumption. The homogeneity range of $\text{La}{}_{\mathrm{1?x}}\text{Al}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext><mtext>3\; +\; x</mtext>}}\text{O}{}_{19}\text{: Eu}{}^{\mathrm{2+}}$ is at such values of x that a large number of Al vacancies exist. Quenching of its luminescence by the introduction of oxygen vacancies was not observed. In LaMgAl₁₁O₁₉ : Eu²⁺ phosphors Al³⁺ interstitials rather than oxygen defects seem to play a dominate role in achieving charge neutrality.