Identification of Eu oxidation states in a doped Sr₅(PO₄)₃F phosphor by TOF-SIMS imaging

An Eu-doped Sr₅(PO₄)₃F phosphor with a hexagonal apatite structure was prepared by a urea assisted combustion method. There was evidence of the reduction of Eu³⁺to Eu²⁺based upon the photoluminescence data. This was confirmed with X-ray photoelectron spectroscopy. Normally it is very difficult to distinguish between two oxidation states with time-offlight secondary ion mass spectrometry (TOF-SIMS), but it is shown that the parallel detection capability of the technique allows full molecular and isotopic characterization of the matrix chemistry. The two states were detected by the EuF+ and EuF2 + species, ostensibly the Eu(II) and Eu(III) oxidation states, respectively.