Influence of local structure on photoluminescence properties of Eu3+ doped CeO2 red phosphors through induced oxygen vacancies by contrasting rare earth substitutions

Abstract

A new family of red phosphors, Ce_0.9−xRE_xO_2−δ:0.1Eu³⁺ (RE = Y and La; x = 0, 0.20, 0.40, 0.60, 0.80, and 0.90), was synthesized by a conventional solid-state route. The influence of contrasting rare earth substitutions (Y and La) in the system was investigated on the local structure and associated photoluminescence properties by various characterization techniques. Both trivalent ion substitutions lead to the same kind of variation during phase transformation from fluorite to the respective parent oxide structure (x ≥ 0.6). On the other hand, the substitutions have a distinct effect on local structure, absorption, luminescence and lifetimes. The smaller Y³⁺ ion substitution enables the ordering of oxygen vacancies in a lattice, inhibiting the defect formation of Ce³⁺ oxidation states. In contrast, the larger La³⁺ ion substitution liberates oxygen vacancies, allowing defect formation. Consequently, the concentration of Ce³⁺ is dependent on the ionic radius of the metal ions and it has a bearing on the band gap and luminescence properties of the system. Ce_0.1Y_0.8O_2−δ:0.1Eu³⁺ phosphor exhibited maximum red emission intensity at 612 nm, which is 8 times higher than that of Ce_0.9O_2−δ:0.1Eu³⁺ and better than that of commercial Philips red phosphor, whereas La substitution yielded poor emission intensities with higher concentrations. The co-substitution of contrasting rare earth metals with Eu³⁺ allow the understanding of local structure and a smaller ion like Y³⁺ greatly functionalizes CeO₂:Eu³⁺ phosphor.