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