The influence of Si4+ co-doping on the spectroscopic properties of β-NaCaPO4:Eu2+/Eu3+

Abstract

A series of luminescent materials based on a sodium calcium phosphate matrix doped with europium and different concentrations of silicon ions was synthesized using the Pechini method. A two-step strategy of synthesis was applied. The phase composition analysis as well as spectroscopic measurements were performed to characterize the obtained phosphors. The XRD patterns show that in all cases the obtained materials consist of a pure phase of β-NaCaPO₄. Emission spectra of the materials obtained after the first step of the synthesis consist of narrow bands attributed to ⁵D₀ → ⁷F_J transitions in Eu³⁺ ions. However, for the materials co-doped with silicon ions, an additional Eu³⁺ site is observed, which is not observed for materials doped only with europium. The emission spectra of the materials after the reduction process are characterized by an intensive broad band attributed to the d–f transitions in Eu²⁺ and narrow bands at 619 nm attributed to the Eu³⁺ ion (incorporation of silicon ions causes the stabilization of the Eu³⁺ ions under a reductive atmosphere).