Eu3+ Spectroscopy: A Structural Probe for Yttrium Orthoborate Phosphors

Yttrium orthorborate YBO3 containing 0.5 or 5 atom % of Eu3+ has been prepared by the spray-pyrolysis method. Low-temperature, high-resolution emission spectroscopy has been used to probe the local site symmetries of Eu3+ ions accommodated on the Y3+ sites in YBO3:Eu3+ (0.5 atom %) and hence to determine the crystal structure of the title compound. The use of point group selection rules enabled a consistent spectral interpretation by envisaging distinct C-i and C-1 symmetry Eu3+ sites, in accordance with the neutron diffraction study of Lin et al. (Chem. Mater. 2004, 16, 2418). The assignment of features in the 10 K visible absorption spectrum of YBO3:Eu3+ (5 atom %) is also consistent with the two-site model, but it was found that the site occupation by Eu3+ differs from the expected ratio 2C(1):1C(i). The fitting of 31 crystal-field levels of the C-1 site has been made with some approximations by employing 7 parameters. In addition, the emission spectrum of YBO3:Eu3+ containing a trace amount of Y3BO6 has been compared with those of YBO3:Eu3+ and Y3BO6: Eu3+, which serves as a reference to elucidate the concern on the red/orange color ratio of YBO3:Eu3+ emission.