The Impact of Different Alkali Metal Ions on Photoluminescence Properties of Ca<sub>10</sub>M(PO<sub>4</sub>)<sub>7</sub>:Eu<sup>2+</sup> (M: Li, Na, K)

Abstract

A series of novel luminescent materials Ca10M(PO4)7:Eu2+(M: Li, Na, K) were synthesized by the solid-state reaction. The previous literatures indicate that the doped different alkali metal ions can only lead to regular shift of the emission and excitation spectra. Howerver, in this paper, we found the result that these three kinds of phosphors showed huge differences between the emission spectra intensity as well as the positions of the excitation and emission spectra peaks. No any regulars can be found. In order to explore it, crystal structure, the performance of photoluminescence spectra and CIE coordinates have been systematically investigated and discussed. In Ca10Li (PO4)7, Ca10Na (PO4)7and Ca10K(PO4)7host lattices, the positions of the cations are different, leading to three different crystal structures. Besides, the coordination conditions of the luminescent centers Eu2+ions are also changed by the incorporation of the alkali metal ions. Thus the enormous disparity on the luminescence intensity as well as the excitation and emission peak positions may be ascribed to these three quite different crystal fields and different coordination numbers of the luminescent central ion in the Ca10M(PO4)7:Eu2+(M: Li, Na, K) phosphors.