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 4f₁→5d₁ 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⁺ 4f₁ and 5d₁ levels within the host band gap are derived and discussed in association with the strong thermal quenching of luminescence as observed experimentally. - Highlights: • Site occupation of Ce³⁺ in Y₃Si₅N₉O was studied by first-principles calculations. • Spectroscopic properties of Ce³⁺ were correlated with the local structures. • Electronic properties were investigated for Ce³⁺ in 4f¹ ground states.