Site occupation and spectroscopic properties of Ce3+ in Y3Si5N9O from first-principles calculations

Abstract It was recently reported that Ce-doped Y 3 Si 5 N 9 O phosphors displayed an extra broad emission band in the range of 450–850 nm arising from 4f−5d transitions of Ce 3+ located at the two crystallographically distinct yttrium sites. Here, a combination of hybrid density functional theory (DFT) and wave function based-CASSCF/CASPT2 calculations at the spin-orbit level has been performed on atomic and electronic structures of the material to gain insights into the site occupation of Ce 3+ and its correlation with spectroscopic properties. It is found that, although Ce 3+ prefers to occupy the eight-coordinated Y2 site over the seven-coordinated Y1 site, the higher intensity emission at the longer wavelength originates from Ce 3+ on the less preferred Y1 site, in support of previous qualitative interpretations. Moreover, the redshift of the lowest 4f 1 →5d 1 transition of Ce 3+ at the Y1 site with respect to that at the Y2 site is rationalized in terms of the variations of 5d centroid energy and crystal-field splitting with the local environment. Finally, the energy positions of Ce 3+ 4f 1 and 5d 1 levels within the host band gap are derived and discussed in association with the strong thermal quenching of luminescence as observed experimentally.