Tunable luminescence properties and elucidating the electronic structures of single-phase spherical bawo₄:Dy³⁺,tm³⁺,eu³⁺ phosphors for warm-white-lighting

A series of uniform single-phase spherical BaWO₄:Dy³⁺,Tm³⁺,Eu³⁺ phosphors were prepared via a microwave hydrothermal method by using trisodium citrate dehydrate as surfactant. The phase structure, morphology and photoluminescence properties were measured by powder X-ray diffraction, scanning electron microscope and fluorescence spectrometer, respectively. The results show that uniform spherical microcrystals with diameters in the range of 2–4 μm are obtained. And the phase and morphology of samples are not significantly changed by doping rare earth (RE³⁺) ions. Under the excitation wavelength of 356 and 365 nm, the samples BaWO₄: 0.03Dy³⁺, yTm³⁺ can emit cold white light. In order to lower the correlated color temperature (CCT) to get a warm white light, the Eu³⁺ ions were doped into BaWO₄: 0.03Dy³⁺, 0.01Tm³⁺. Especially, under the excitation of 365 nm, BaWO₄: 0.03Dy³⁺, 0.01Tm³⁺, 0.03Eu³⁺ phosphor shew a bright warm white light with color coordinate of (0.4013, 0.3629) and CCT of 3288 K. Moreover, in the BaWO₄:Dy³⁺,Tm³⁺,Eu³⁺ phosphors, the energy transfer mechanism among Dy³⁺,Tm³⁺ and Eu³⁺ ions have been discussed and the change of electron structures have been calculated by first-principles calculations. The results shew that the uniform single-phase spherical BaWO₄:Dy³⁺,Tm³⁺,Eu³⁺ phosphors could be favorable candidates in warm white LEDs.