High frequency EPR of europium(ii)-doped strontium aluminate phosphors

Abstract

The europium(II) sites in Sr4Al 14O25 ∶ Eu phosphor with blue emission were examined by means of high frequency (90 and 180 GHz) EPR spectroscopy. The ions occupy two low symmetry sites in the Sr4Al 14O25 lattice with |D| = 0.100 and 0.0907 cm−1 respectively; the ratio |E/D | is estimated to be 1/3 regardless of the substitution site. This implies that the crystal field surrounding europium(II) ions has non-axial symmetry. EPR spectral simulation suggests that the europium( II) ions preferentially occupy the site with the larger |D | when they substitute for strontium ions. Comparison of the EPR spectra of Sr4Al14O25 ∶ Eu and SrAl2O4 ∶ Eu,Dy phosphors shows that the Sr4Al14O25 ∶ Eu is present as an impurity in the non-stoichiometric SrAl2O 4 ∶ Eu,Dy when prepared with excess amounts of Al 2O3. Such materials have been found to have long phosphorescent characteristics.