Optical absorption and luminescent behaviour of Ruddlesden-Popper type Sr2(Ce1-xFex)O4 (x = 0–1.0) oxides

Abstract

An attempt has been made to synthesise iron-doped Sr2(Ce1-xFex)O4 (x = 0–1.0) oxides and characterized with regards to optical absorption and photoluminescence. It exhibits single (orthorhombic), dual (orthorhombic + tetragonal), and single (tetragonal) phase formation with x = 0–0.03, 0.05–0.80, and 0.90–1.0, respectively. The peaks observed at ∼2.71 and ∼2.44 eV (say; x = 0) in photoluminescent spectra are assigned to the charge transfer transition between Ce–O2 and Ce–O1, respectively. These states are arising due to the length difference between terminal and equatorial Ce–O bonds in the CeO6 octahedron. The composition Sr2FeO4 (x = 1.0) depicts peaks at 2.66 and 2.56 eV related to the charge transfer transition (CTT) between Fe–O of FeO6 octahedra. The excitation spectrum Sr2(Ce0.80Fe0.20)O4 exhibits two peaks around 5.84 and 4.90 eV related to the different Ce4+ - O2− distances in the lattice. Moreover, shifting of peaks refers to red shift in spectra and arises due to decrease in Ce–O bond length. The optical absorption peak at 261 nm (say; x = 0) is attributed to transitions from O(2p) to Ce(4f) in the O2− and Ce4+ states. The band gap decreases (3.73–3.59 eV) with iron, and supporting our photoluminescent spectra.