ABSTRACT
PrLuO3 interlanthanides were prepared at temperatures ranging from 800 °C to 1600 °C using hydrothermally-derived precursors. The chemical reactions observed include the conversion and segregation of Pr(OH)3 and LuO(OH), respectively, into PrO2 and Lu2O3 cubic oxides below 1200 °C, followed by the production of a mixture of hexagonal P63/mmc and orthorhombic Pnma PrLuO3 phases at 1400 °C. Phase-pure orthorhombic PrLuO3 was obtained at 1600 °C, which was corroborated by Raman and micro far-infrared spectroscopic analyses. Photoluminescence, colorimetric and lifetime measurements were carried out in PrLuO3 samples. Dominant emission verified in samples calcined at 1400 °C corresponds to the hypersensitive 3P0 â 3F2 transition with a color purity of 97% (decay times of 12 µs and 3 µs), while emissions for the phase-pure samples correspond to the 3P0 â 3H6 and 3P0 â 3H5 transitions with a color purity of 94% (a single luminescence lifetime of 12 µs). The optical properties of PrLuO3 interlanthanides thereby suggest that they can be used as luminescent materials in both structural arrangements.
ABSTRACT
Lanthanide orthotantalates RETaO(4) (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) were synthesized by solid-state reaction in optimized conditions of temperature (1300 °C) and time (up to 14 h) to yield crystalline materials. The crystal structures of the obtained compounds were investigated by X-ray diffraction and Raman scattering. All the samples exhibited monoclinic structures, but with different arrangements as a function of the ionic radius of the rare-earth metal occupying the A-site. For compounds with the largest ionic radii (La-Pr), the ceramics crystallized in the monoclinic structure, P2(1)/c (C(2h)(5), #14, Z = 4), while the compounds with intermediate ionic radii (Nd-Tb) exhibited the fergusonite M-type structure, I2/a (C(2h)(6), #15, Z = 4). Samples with the smallest ionic radii (Dy-Lu) presented the fergusonite M'-type structure, P2/a (C(2h)(4), #13, Z = 2). These last two groups of compounds exhibited phase transitions, which can be related to the processing temperature. The compounds belonging to the M-type structure are stable at high temperatures, whilst materials belonging to the M'-type structure are stable at low temperatures. The results from XRD and Raman scattering allows us to understand the differences between these two structures in terms of the vibrational-active modes assigned to each space group. Also, the Raman patterns in addition to group-theory calculations for this complete lanthanide series were reported for the first time. The experimental results are in perfect agreement with theoretical calculations: samples with P2(1)/c (#14) structure showed 36 Raman-active modes, while both I2/a (#15) and P2/a (#13) structures exhibited 18 Raman modes.
