High-frequency EPR investigation of X-ray storage SrBPO5:Eu phosphor

High-frequency EPR (HFEPR) spectra of the SrBPO5:Eu with stillwellite structure, which was prepared using EuCl3.6H(2)O as a dopant, have been examined in order to clarify the Eu sites in it. They showed an intense doublet at 3.3 T corresponding to g = 2.0 as is expected for the S-8 state ions. Also, weak satellites were observed on both sides of the central doublet signal symmetrically. This means that microwave energy at 90 GHz is sufficiently larger than the zero-field splitting. Taking into account the crystal structure of stillwellite and the earlier PL investigation, a single Eu2+ site was assumed for the HFEPR simulation. As a result, it was found that HFEPR spectrum simulated using g = 1.98161, 1 D I = 0.130T and lambda = \E/D\ = 0.06 reasonably agrees well with the experimental one, supporting that the Eu2+ occupies the Sr site. The large I D I value small lambda value obtained implies that the crystal field surrounding Eu2+ has a strong axial field with weak rhombic distortion. (C) 2003 Elsevier Science B.V. All rights reserved.