Luminescence properties of calcium tungstate activated by lanthanide(III) ions

Calcium tungstate phosphors activated by the Ln(3+) ions (Ln-Pr, Nd, Tb, Yb) were synthesized by a traditional high-temperature solid-state method. The crystal structures and morphologies of the products were characterized by scanning electron microscopy (SEM), X-ray powders diffraction (XRD) and infrared spectra (FT-IR). The samples were found to show luminescence properties (down-conversion, DC, at excitation wavelength 254 urn and up-conversion, UC, at excitation wavelength 980 nm). CaWO4 doped with Tb3+/Yb3+ showed green DC and UC luminescence characteristic of Tb(M) ion in the range of 470-660 nm, corresponding to the D-5(4)-> F-7(6,5,4,3,2) electronic transition. CaWO4 doped with Pr3+/Yb3+ showed week blue, green and red (DC and UC) luminescence of Pr(III) ion, in the wavelength region of 450-700 nm. Emission peaks were ascribed to the P-3(1)-> H-3(4,5,6), P-3(0)-> H-3(4,5,6), P-3(1)-> F-3(2) and P-3(0)-> F-3(2) transitions, respectively. CaWO4 doped with Nd3+/Yb3+ phosphor emitted orange UC luminescence at 450-690 nrn (P-2(3/2)-> I-4(15/2), (4)G(7/2)-> I-4(9/2,11/2,13/2)) and strong near-infrared UC luminescence at 720-900 nm (F-4(7/2)+S-4(3/2)-> I-4(9/2), F-4(5/2) + H-2(3/2)-> I-4(9/2), F-4(3/2)-> I-4(9/2)) which is the characteristic of Nd(III) ion.