Charge-Transfer Luminescence and Energy Transfer in Eu(2+)-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 BaZrSi(3)O(9) and Ba(2)Zr(2)Si(3)O(12) using synchrotron radiation, and examined the possibility of sensitizing Eu(2+) by hosts that contain zirconate. Upon VUV excitation, BaZrSi(3)O(9) and Ba(2)Zr(2)Si(3)O(12) show self-activated emission peaking at 285 nm and 334 nm, which are assigned to Zr(4+)-O(2-) charge transfer (CT) luminescence. The evidence for the occurrence of Zr(4+)-O(2-) charge transfer in BaZrSi(3)O(9) and Ba(2)Zr(2)Si(3)O(12) was further supported by density of state (DOS) calculation. Energy transfer from host excitation (similar to 172 nm) to Eu(2+) was observed in BaZrSi(3)O(9):Eu(2+) and Ba(2)Zr(2)Si(3)O(12):Eu(2+), showing that host sensitization of Eu(2+) occurs in these materials. Despite that the host emission overlaps with the Eu(2+) 4f-5d absorption band significantly, host -to-Eu(2+) energy transfer in Ba(2)Zr(2)Si(3)O(12):Eu(2+) was found to be less efficient than that in BaZrSi(3)O(9):Eu(2+) and Eu(2+) luminescence was found to be inferior in Ba(2)Zr(2)Si(3)O(12):Eu(2+). These observations are ascribed to a smaller Zr-O-Ba(Eu) angles and a lower Eu(2+)-Zr(4+) metal-to-metal charge transfer energy in Ba(2)Zr(2)Si(3)O(12):Eu(2+). (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.008112jes] All rights reserved.