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Terbium orthotantalate powders were produced with M-fergusonite type (I2/a) and M 0-fergusonite type (P2/a) structures. The samples were studied by X-ray diffraction, Raman scattering, and photoluminescence measurements (emission and decay curves). The results showed that crystalline materials were obtained with all the 18 Raman-active modes predicted by group theory calculations. Also, it was observed through photoluminescence decay curves that the Tb 3 þ ions occupies only onesymmetry site in both crystallographic arrangements. Photoluminescence emission curves exhibited some variation in spectral shape, peak position, and relative intensity as a consequence of their different crystalline arrangements. The dominated emission of Tb 3 þ (5 D 4-7 F 5) is centered with a maximum intensity at 549.2 nm (M-type) and 543.0 nm (M 0-type). Fluorescence lifetimes for M-TbTaO 4 and M 0-TbTaO 4 were determined as 33.4 ms and 1.25 ms, respectively. M 0-type materials seems to be the most suitable for luminescent devices and could be a potential green luminescent material due to the strongest emission if compared with the M-fergusonite type.

Experimental evidence has been observed for energy transfer from CdS nanocrystals, synthesized by the fusion method, to Nd(3+) ions embedded in vitreous substrates. These dot samples doped with neodymium have been investigated by combined optical absorption (OA), photoluminescence (PL), and time-resolved photoluminescence (PLRT) techniques. Radiative and nonradiative energy transfers between CdS dot and Nd(3+) ion levels, to our knowledge not reported before, can be clearly observed in the PL spectra where the emission band valleys correspond exactly to the energy absorption peaks of the doping ion. The PLRT data reinforce these energy transfer mechanisms in which the increasing overlap between the CdS PL band and the OA to the Nd(3+) levels decreases stimulated emissions from the doping ions.