Luminescence properties of Tm3+/Yb3+,Er3+/Yb3+ and Ho3+/Yb3+ activated calcium tungstate

CaWO4 phosphor activated by the Tm3+/Yb3+, Er3+/Yb3+ and Ho3+/Yb3+ ions were synthesized by a traditional high-temperature solid-state method. The crystal structures and morphologies of the products were characterized by X-ray powders diffraction method (XRD), infrared spectra (FT-IR) and scanning electron microscopy (SEM). The samples were found to show up-conversion luminescence properties. CaWO4 doped with Tm3+/Yb3+ showed blue luminescence characteristic of Tm(III) ion in the range of 460-485 nm, corresponding to the (1)G(4)-> H-3(6) electronic transition. CaWO4 doped with Er3+/Yb3+ showed strong green luminescence at 510-565 nm (H-2(11/2), S-4(3/2)-> I-4(15/2)) and weak red luminescence at 640-685 nm (F-4(9/2)-> I-4(15/2)) of Er(III) ion. CaWO4 doped with Ho3+/Yb3+ phosphor emitted green luminescence at 525-560 nm (S-5(2), F-5(4)-> I-5(8)) and red luminescence at 630-670 nm (F-5(5)-> I-5(8)) and at 730-770 nm (S-5(2), F-5(4)-> I-5(7)), which is the characteristic of Ho(III) ion.