27Al MAS NMR spectroscopy study of Eu2+-doped and Dy3+-co-doped SrAl4O7

Abstract

The Eu²⁺-doped strontium aluminate SrAl₄O₇ samples have shown the blue-green persistent luminescence at 490 nm while the co-doping with Dy³⁺ shifts the maximum of emission to 475 nm. Undoped, 3% Eu-doped and 6% Dy-co-doped SrAl₄O₇ samples were prepared by the solid state-reaction method and studied by the solid-state ²⁷Al MAS NMR applying the single pulse-acquire and Hahn-echo pulse sequences. It was shown that the Eu²⁺ with Dy³⁺ ion doping did not affect the bulk structure as well as the local Al environment in SrAl₄O₇. This means that large shifts of the emission maximum cannot be caused by changes in the local environment upon the co-doping of SrAl₄O₇:Eu²⁺ with Dy³⁺. However, the spectral features observed in the range between the signals of 4- and 6-coordinated Al (20–40 ppm) indicate that certain phase imperfections are present in all studied samples, and most probably amorphous/glassy domains were formed. Note that such amount of phase impurities was not detected by standard XRD or FTIR methods. This has revealed the ²⁷Al MAS NMR technique to be a very effective tool monitoring the phase perfectness in series of strontium aluminate samples.