The role of hypersensitive transition in Eu3+ optical probe for site symmetry determination in BaScBO-SrScBO solid-solution phosphor

Abstract

Ba3Sc(BO3)3 – Sr3Sc(BO3)3 solid-solution was synthesized by conventional solid-state method with Sr2+ concentration 0%, 25%, 50%, 100%. The Eu3+ has been used as an optical probe to determine the site symmetry of studied host. Ba3Sc(BO3)3 (BaScBO) has six sites Eu3+ can enter: four Ba2+ 9-coordinated sites and two Sc3+ 6-coordinated sites. Sr3Sc(BO3)3 (SrScBO) has only three: one Sr2+ 9-coordinated site and two Sc3+ 6-coordinated sites. The luminescence from Eu3+ at Sc3+ sites was observed at 10 K only. At 77 K only luminescence from Eu3+ at Sr/Ba2+ sites was observed.With increasing Sr2+ concentration the luminescence decay time increases and the R parameter (electric dipole transitions to magnetic dipole transitions ratio) decreases.The Judd-Ofelt analysis reveals, that only the intensity of hypersensitive 5D0 → 7F2 transition decreases with Sr2+ concentration, while the intensity of the remaining electric dipole transitions (5D0 → 7F4 and 5D0 → 7F6) increases. The decrease of the intensity of the hypersensitive transition results from the lower refractive index, not from the higher site symmetry.The studies explicitly reveal the importance of considering the refraction index in the optical probe method.