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

Calcium tungstate phosphors activated by the Ln3+ 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 nm and up-conversion, UC, at excitation wavelength 980 nm). CaWO4 doped with Tb3+/Yb3+ showed green DC and UC luminescence characteristic of Tb(III) ion in the range of 470–660 nm, corresponding to the 5D4→7F6,5,4,3,2 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 3P1→3H4,5,6, 3P0→3H4,5,6, 3P1→3F2 and 3P0→3F2 transitions, respectively. CaWO4 doped with Nd3+/Yb3+ phosphor emitted orange UC luminescence at 450–690 nm (2P3/2→4I15/2, 4G7/2→4I9/2,11/2,13/2) and strong near-infrared UC luminescence at 720–900 nm (4F7/2+4S3/2→4I9/2, 4F5/2+2H3/2→4I9/2, 4F3/2→4I9/2) which is the characteristic of Nd(III) ion.

Ln3+:CaWO4 doped with Tb3+/Yb3+, Pr3+/Yb3+ and Nd3+/Yb3+ luminescence phosphors synthesized using a solid-state method showed interesting luminescence properties (downconversion, DC, at excitation wavelength 254 nm and up-conversion, UC, at excitation wavelength 980 nm). The upconversion luminescence intensity increased in the series of Pr3+/Yb3+