Structural investigation of Eu2+ emissions from alkaline earth zirconium phosphate

Eu2+ doped A0.5Zr2(PO4)3 (A=Ca, Sr, Ba) phosphors with the NASICON structure were synthesized by a co-precipitation method. Their photoluminescent and structural properties were investigated by photoluminescent spectroscopy and powder X-ray Rietveld analysis, which determined two sites for Eu2+ ions in the host structure, 3a and 3b. The Eu–O bond lengths were increased by changing alkaline earth ions from Ca to Ba, causing Eu2+ emission bands to shift from blue-green to blue. A correlation was observed between the peak wavelength positions and the Eu–O bond length. The photoluminescent properties are discussed in terms of crystal field strength and nephelauxetic effect, and a schematic diagram of Eu2+ emissions is proposed for the Eu2+ doped NASICON phosphor.