Doping Eu3+/Sm3+ into CaWO4:Tm3+, Dy3+ phosphors and their luminescence properties, tunable color and energy transfer

Abstract

In order to obtain warm white light emission, Eu³⁺ or Sm³⁺ ions were incorporated into CaWO₄:Tm³⁺, Dy³⁺ phosphors via a one-step hydrothermal method without further sintering. The as-synthesized samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and photoluminescence (PL) spectra. Upon UV light (355 nm and 365 nm) excitation, the phosphors exhibit blue emission of Tm³⁺ ions, yellow-blue emission of Dy³⁺ ions and red emission of Eu³⁺ ions (or red-orange emission of Sm³⁺ ions). The quenching concentration of Dy³⁺ is determined to be about 1.0%. The critical distance between Tm³⁺ and Dy³⁺ has been calculated to be about 16.4 Å and the energy transfer from Tm³⁺ to Dy³⁺ occurs through the quadrupole–quadrupole interaction. The color tone of the obtained phosphors is easily modulated to warm-white-light by co-doped Eu³⁺ or Sm³⁺. Furthermore, the influence of the rare earth ion emission intensities under different excitation wavelengths (355 nm and 365 nm), and the doped concentration of Eu³⁺ or Sm³⁺ ions on the luminescence properties for the CaWO₄:Tm³⁺, Dy³⁺ phosphor were measured and discussed. These results reveal that this kind of phosphor is a potential candidate for white LEDs.