Abstract
Some III-group impurities, e.g. B^<3+>, Sc^<3+>, Y^<3+> or Gd^<3+>, added to a red phosphor SrIn_20_4:Pr^<3+> for low-energy electron excitation, improve luminescence efficiency, while another impurity, La^<3+>, decreases efficiency. This work investigates the mechanism of this impurity effect, particularly the difference between Gd^<3+> and La^<3+> in improving efficiency. The sites where these ions replace in SrIn_20_4 lattice are discussed with powder X-ray diffraction and luminescence spectra measurements. The impurity effect on luminescence efficiency is discussed based on a following model; III-group impurities substituting In^<3+> site improve the luminescence efficiency of Pr^<3+> by capturing electrons in competition with oxygen ion vacancies, which work as nonradiative centers at higher temperature. In contrast III-group impurities substituting Sr^<2+> site decreases efficiency by increasing oxygen ion vacancies.
