Observation, identification and characterization of strong self-reduction process in a orthophosphate phosphor CaZr4(PO4)6:Eu

• CaZr4P4O24:Eu was synthesized by solid state reaction in air.
• Relationship between the structure and luminescence properties was discussed.
• Strong self-reduction process was found in CaZr4P4O24:Eu prepared in air.
• Oxidation states of Eu were identified by muti-method approaches.
• The self-reduction mechanism was investigated.

CaZr4P4O24:Eu orthophosphate phosphor was synthesized by traditional solid state reaction in air atmosphere. The relationship between the host structure and the characteristic luminescence properties was discussed detailedly. When irradiate the sample under 365 nm UV lamp, intense green emission was observed due to the strong self-reduction process of Eu ions. The oxidation states of Eu ions were identified by muti-method approaches, including photoluminescence spectra, fluorescence lifetimes, Electron spin resonance (ESR) spectroscopy and X-ray photoelectron spectroscopy analysis (XPS). The self-reduction process was controlled by adding the charge compensator Li2CO3 and the self-reduction mechanism was further investigated.

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