Untitled

Spectral and structural studies of GdCOB and YCOB crystals

“…Though the GdCOB and YCOB are members of the same family, differences between the two crystals have been reported recently from: DTA data [5,6], single crystals X-ray [7,8] or high resolution optical spectroscopy of Yb 3+ or Nd 3+ [9,10].…”

Spectroscopic study of europium doped RCOB host lattices: evidence of local perturbations

“…The inhomogeneous broadening effects observed for Eu 3+ spectra can be associated to a distribution of the crystal field strength. The second order crystal field parameters depend on the neighbors in the second and further coordination cationic spheres and therefore the observed shifts in 5 D 0 → 7 F 0,1 transitions could be qualitatively explained by the model proposed for RCOB structure [6,7]. The disorder in pure RCOB crystals involves a mixed occupancy of R 3+ and Ca 2+ (1) sites, and the degree of disorder depends only on the R 3+ ionic radius.…”

“…The RE 3+ dopant would also contribute to disorder, since depending on the ionic radius (and concentration) it would be distributed between the two positions by the same rules. The compositions estimated according to [6,7] and this determine an inhomogeneous broadening. The disorder in GdCOB: Eu 3+ is larger than in EuCOB.…”

“…The real structure of RCOB crystals is still under discussion. Recent structural investigations [6,7] based on single crystal X-ray diffraction have proposed, like in [2], a mixed occupancy of R 3+ and Ca 2+ (1) sites. A relation giving the distribution of these ions in the two sites function only on rare earth ionic radius is deduced: the degree of disorder increases if the ionic radius decreases and thus the RCOB compounds are in fact only isotypic and not isostructural.…”

“…These data [15,16] have shown the role of rare earth ionic radii in disordered behavior, explained only qualitatively in terms of charged defects induced by R 3+ ⇔ Ca 2+ inversion. The reanalysis of Nd 3+ and Yb 3+ spectral data in GdCOB and YCOB in terms of structural model [6,7] has shown that the relative concentration of one minor site depends on dopants ionic radii in the same RCOB crystal. The investigation of Eu 3+ ion, situated in the middle of lanthanide series, could bring new information, especially since this ion possess several transitions, such as 7 F 0 ⇔ 5 D 0,1 , very sensitive to the local environment.…”