Ce4+-Based Compounds Capable of Photoluminescence by Charge Transfer Excitation under Near-Ultraviolet-Visible Light

Abstract

Ce⁴⁺-based charge transfer phosphor is not common and has been reported mainly in Sr₂CeO₄ with an excitation band peaking at ∼290 nm, mismatching with the near-ultraviolet light emitting diodes. Herein, we report a new series of Ce⁴⁺-based compounds Sr_4.4Ce_2.6REZnO₁₂ (RE = Y, La, and Eu) capable of photoluminescence induced by O^2--Ce⁴⁺ charge transfer excitation under near-ultraviolet-visible light. The crystal structure of Sr_4.4Ce_2.6EuZnO₁₂ was determined by single crystal X-ray diffraction. The RE = La and Y samples were confirmed to be iso-structure compounds of the RE = Eu sample by powder X-ray diffraction. By introducing highly covalent Zn²⁺-O^2- bonds into the framework, the Ce⁴⁺-O^2- bonds are lengthened due to the effect of the Ce⁴⁺-O^2--Zn²⁺ stretch. The lengthened Ce⁴⁺-O^2- bond weakens the repulsion of the electrons between Ce⁴⁺ and O^2-, thereby lowering the charge transfer energy to the visible light region. Incorporation of Eu³⁺ into the present compounds realized red emission under near-ultraviolet-visible excitation by the O^2--Ce⁴⁺ charge transfer followed by energy transfer to Eu³⁺.