Charge-Transfer Luminescence and Energy Transfer in Eu2+-Doped Barium Zirconosilicates

Abstract

Although zirconates are known to show ultraviolet luminescence under X-ray excitation, few have studied the vacuum ultraviolet (VUV) excited luminescence of zirconate compounds. We have investigated the VUV-excited luminescence of zirconate in BaZrSi3O9 and Ba2Zr2Si3O12 using synchrotron radiation, and examined the possibility of sensitizing Eu2+ by hosts that contain zirconate. Upon VUV excitation, BaZrSi3O9 and Ba2Zr2Si3O12 show self-activated emission peaking at 285 nm and 334 nm, which are assigned to Zr4+-O2− charge transfer (CT) luminescence. The evidence for the occurrence of Zr4+-O2− charge transfer in BaZrSi3O9 and Ba2Zr2Si3O12 was further supported by density of state (DOS) calculation. Energy transfer from host excitation (∼172 nm) to Eu2+ was observed in BaZrSi3O9:Eu2+ and Ba2Zr2Si3O12:Eu2+, showing that host sensitization of Eu2+ occurs in these materials. Despite that the host emission overlaps with the Eu2+ 4f-5d absorption band significantly, host -to-Eu2+ energy transfer in Ba2Zr2Si3O12:Eu2+ was found to be less efficient than that in BaZrSi3O9:Eu2+ and Eu2+ luminescence was found to be inferior in Ba2Zr2Si3O12:Eu2+. These observations are ascribed to a smaller Zr-O-Ba(Eu) angles and a lower Eu2+-Zr4+ metal-to-metal charge transfer energy in Ba2Zr2Si3O12:Eu2+.