Optical study of SrAl1.7B0.3O4:Eu, R (R=Nd, Dy) pigments with long-lasting phosphorescence for industrial uses

We have studied and compared the optical properties of SrAl1.7B0.3O4:Eu, R (R=Nd, Dy) pigments that present long-lasting phosphorescence obtained by different synthesis techniques. Samples obtained by ceramic methods, in our laboratories and by an industrial process, present better phosphorescent properties than those obtained by sol-gel technique. Raman spectra show that grinding produces severe damage of the lattice. We have obtained and analyzed the Eu3+ crystal field luminescence indicating that Eu3+ is found in quite different sites comparing ceramic and sol-gel samples. Codoping, with Nd or Dy is necessary in order to reduce the Eu3+ content, in all cases. The green luminescence band, obtained under UV illumination, can be fitted to two and three components in ceramic and sol-gel samples, respectively, due to different Eu2+ sites. Eu-Dy samples present the longest and the most efficient phosphorescence. The time evolution of the afterglow is well described by a t-1 law, up to about 2 h, indicating that the recombination process is achieved by electron-hole tunneling