Excitation-dependent variation in local symmetry in Ba2Mg(BO3)2 evidenced by Eu3+ luminescent structural probe

Abstract

Eu3+ luminescence was studied in Ba2Mg(BO3)2 by selectively substituting at Mg site. The parent host Ba2Mg(BO3)2 and Ba2Mg0.9Eu0.05Li0.05(BO3)2 were synthesized by conventional solid state reaction method. Their isostructural nature was confirmed using powder X-ray diffraction technique. The photoluminescence excitation spectrum of Eu3+ exhibited a broad Eu3+O2− charge transfer band with a maximum at 253 nm along with other excitation transitions. The emission characteristics of Eu3+ were found to be excitation wavelength-dependent. The equally intense magnetic and electric dipole transitions for excitation under longer wavelengths showed the presence of Eu3+ at a site with non-inversion symmetry. Excitation using 253 nm resulted in the predominant magnetic dipole transition revealing Eu3+ at a site with inversion symmetry. The difference in the relative intensities of magnetic and electric dipole transitions originates from the change in symmetry around Eu3+ in Ba2Mg(BO3)2 under different excitations.