The luminescence properties ofEu 3+ and Tb 3+ in Y30+C1, Y304Br, and Gd304Br, a family of oxyhalides with high chemical stability, have been investigated. The emission results from rare earth ions lying in two different sites. Spectral distributions and efficiencies are compared to those of the related Eu ~ § or Tb 3 § doped LnOX compounds. The efficiency is of the same order of magnitude for UV excitation into the Eu 3+ charge transfer or Tb 3 § 5d bands, but much lower for excitation through the host lattice (i.e., by x-ray or electron beam).Although the luminescent properties of the LnOX (Ln = rare earth, X = C1, Br) oxyhalides have been thoroughly investigated (1-5), little is known about those of the Ln304X-type. The first members of this familly (Sm304Br, Eu304Br, and Yb304Br) have been discovered by Barnighausen et al. (6). Afterwards the existence of tetraoxybromides has been mentioned for Ln = Pr, Nd, Gd, and Y (7, 8). They have been obtained from the LnOBr phases either by decomposition in air, 6LnOBr + 02 --~ 2Ln~O4Br + 2Br2, or, except for Y304Br, by reaction with the Ln203 oxides, LnOBr + Ln203 ---> Ln30~X. The tetraoxychlorides Ln304C1 have been prepared only for the small rare earth ions (Y, Er, Tm, Yb, Lu), from the PbC1F-type variety of the LnOC1 oxychlorides (9, 10).Unlike most LnOX phases the tetraoxyhalides show high chemical stability. The luminescent properties of rare earth ions in those compounds have been mentioned in a patent (11); no information on the luminescence efficiency is given.For various reasons, in particular the wide gap between the emitting level and the next lowest level (Fig. 1), Eu 3 § and Tb 3 § are obviously the most favorable rare earth ions for visible emission. Hence we have investigated the luminescence properties of these ions in the host lattices: Y304C1, Y304Br, and Gd304Br. In agreement with previous publications (7-9), all attempts to prepare La304C1, Gd304C1, or La30,Br were unsuccessful.
Synthesis and Structural Features of the Ln~O4X PhasesIn the case of the oxybromides, the rare earth oxides (4N, Rh6ne-Poulenc) were dissolved in a HBr solution (Prolabo) which was evaporated to dryness. The residue (a mixture of hydrated bromide and LnOBr) was converted 3O 20 10 0 E(x 103cm -1) % 'D, 'Oo 7F o __ + --5 --4 4 --5 --
