Optical properties of Eu²⁺ /Eu³⁺ mixed valence phosphor Ca₂ SiO₂ F₂ :Eu²⁺ /Eu³

The Eu²⁺ /Eu³⁺ mixed valence phosphor Ca₂ SiO₂ F₂ :Eu²⁺ /Eu³⁺ was prepared using a solid-state reaction synthesis method in a CO atmosphere, and the optical properties were investigated. The spectroscopic properties revealed that Ca²⁺ ions were occupied by both Eu²⁺ and Eu³⁺ ions in Ca₂ SiO₂ F₂ , and both ions were able to generate their characteristic emissions. A broad 5d → 4f Eu²⁺ band at ~470 nm and narrow 4f → 4f Eu³⁺ peaks upon excitation with n-UV light were observed. The ratio between Eu²⁺ and Eu³⁺ emissions changed regularly, and the relative intensity of the red component from Eu³⁺ became systematically stronger with increasing overall Eu content. As a result, the emission color of these phosphors can be tunable from blue to pink under n-UV light excitation.