The influence of charge compensation defects on the spectroscopic properties of europium doped Ca9Y(PO4)7

Abstract

In this study, a series of Ca₉Y(PO₄)₇ compounds doped with 5% of Eu ions and with different [Y]/[Ca] ratios was synthesized using the Pechini method. Due to the presence of two different cations in the studied matrix (Ca²⁺ and Y³⁺) that are available for europium substitution, the synthesis parameters were selected to obtain the incorporation of the europium ions (5% mol) into the calcium sites only. The phase composition as well as elemental analysis and the spectroscopic measurements, carried out before and/or after the reduction of Eu³⁺ were performed to characterize the obtained phosphors. The XRD patterns show that in all cases the obtained materials consist of pure phase of Ca₉Y(PO₄)₇. PLE and PL spectra measured before the reduction indicate that for the materials with the excess of yttrium, an additional Eu³⁺ site is observed which was not observed for materials with a deficiency of yttrium. For samples obtained after the reduction, the luminescence of Eu²⁺ depends on the changes of the Y/Ca ratio. The observed differences in Eu²⁺ luminescence are discussed taking into account the creation of different compensation defects depending on change of the Y/Ca ratio.