Nanostructured CaWO₄, CaWO₄:Eu³⁺ and CaWO₄:Tb³⁺ Particles: Sonochemical Synthesis and Luminescent Properties

Abstract

Nanostructured CaWO 4 , CaWO 4 :Eu 3+ , and CaWO 4 :Tb 3+ phosphor particles were synthesized via a facile sonochemical route. X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, low voltage cathodoluminescence spectra, and photoluminescence lifetimes were used to characterize the as-obtained samples. The X-ray diffraction results indicate that the samples are well crystallized with the scheelite structure of CaWO 4 . The transmission electron microscopy and field emission scanning electron microscopy images illustrate that the powders consist of spherical particles with sizes from 120 to 160 nm, which are the aggregates of even smaller nanoparticles ranging from 10 to 20 nm. Under UV light or electron beam excitation, the CaWO 4 powder exhibited a blue emission band with a maximum at 430 nm originating from the WO 2− 4 groups, while the CaWO 4 :Eu 3+ powder showed red emission dominated by 613 nm ascribed to the 5 D 0 → 7 F 2 of Eu 3+ , and the CaWO 4 :Tb 3+ powders showed emission at 544 nm, ascribed to the 5 D 4 → 7 F 5 transition of Tb 3+ . The PL excitation and emission spectra suggest that the energy is transferred from WO 2− 4 to Eu 3+ CaWO 4 :Eu 3+ and to Tb 3+ in CaWO 4 :Tb 3+ . Moreover, the energy transfer from WO 2− 4 to Tb 3+ in CaWO 4 :Tb 3+ is more efficient than that from WO 2− 4 to Eu 3+ in CaWO 4 :Eu 3+ . This novel and efficient pathway could open new opportunities for further investigating the novel properties of tungstate materials.