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

It was recently reported that Ce-doped Y3Si5N9O phosphors displayed an extra broad emission band in the range of 450-850 nm arising from 4f-5d transitions of Ce3+ 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 Ce3+ and its correlation with spectroscopic properties. It is found that, although Ce3+ prefers to occupy the eight-coordinated Y2 site over the seven-coordinated Y1 site, the higher intensity emission at the longer wavelength originates from Ce3+ on the less preferred Y1 site, in support of previous qualitative interpretations. Moreover, the redshift of the lowest 4f(1)-> 5d(1) transition of Ce3+ 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 Ce3+ 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. (C) 2017 Elsevier B.V. All rights reserved.