Ce ⁴⁺ -Based Compounds Capable of Photoluminescence by Charge Transfer Excitation under Near-Ultraviolet-Visible Light

Ce ⁴⁺ -based charge transfer phosphor is not common and has been reported mainly in Sr ₂ CeO ₄ with an excitation band peaking at ∼290 nm, mismatching with the near-ultraviolet light emitting diodes. Herein, we report a new series of Ce ⁴⁺ -based compounds Sr _4.4 Ce _2.6 REZnO ₁₂ (RE = Y, La, and Eu) capable of photoluminescence induced by O ^2- -Ce ⁴⁺ charge transfer excitation under near-ultraviolet-visible light. The crystal structure of Sr _4.4 Ce _2.6 EuZnO ₁₂ 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 Zn ²⁺ -O ^2- bonds into the framework, the Ce ⁴⁺ -O ^2- bonds are lengthened due to the effect of the Ce ⁴⁺ -O ^2- -Zn ²⁺ stretch. The lengthened Ce ⁴⁺ -O ^2- bond weakens the repulsion of the electrons between Ce ⁴⁺ and O ^2- , thereby lowering the charge transfer energy to the visible light region. Incorporation of Eu ³⁺ into the present compounds realized red emission under near-ultraviolet-visible excitation by the O ^2- -Ce ⁴⁺ charge transfer followed by energy transfer to Eu ³⁺ .