Eu2+ luminescence in the EuAl2O4 concentrated phosphor

Powder samples of EuAl2O4 and (Eu,Sr)Al2O4 with a quantum efficiency (QE) of the Eu2+ emission more than 0.30 were synthesized. A modified method of QE determination is described and results of the QE measurements for EuAl2O4, (Eu0.8Sr0.2)Al2O4, (Eu0.65Sr0.35)Al2O4, and a diluted sample (Sr0.98Eu0.02)Al2O4 are presented. Excitation and emission spectra as well as decay behaviour of the Eu2+ luminescence in (Eu1-xSrx)Al2O4 in the temperature region of 20-300 K are studied. It is concluded that the main reason for the high QE is a pronounced relaxation of the crystal lattice after excitation of the Eu2+ ions resulting in an emission with a large Stokes shift and, therefore, in a restriction of energy migration. Eu ions occupying the crystallographic sites with the higher coordination number (EuII) are supposed to be the luminescence centres in (EuSr)Al2O4 lattice.