Controllable Synthesis of NaLu(WO₄)₂:Eu³⁺ Microcrystal and Luminescence Properties for LEDs

The phosphors of trivalent rare-earth ion Eu³⁺-activated alkaline double tungstates NaLu­(WO₄)₂ were prepared by the EDTA-assisted hydrothermal method. The crystal structure and morphology of the as-synthesized phosphors were determined by powder X-ray diffraction (XRD) and electron microscopes (SEM and TEM), respectively. The phase and morphology can be controlled by different Eu³⁺-doping concentrations. Not less than 40 at % of Eu³⁺ doping concentration pledged the NaLu­(WO₄)₂:Eu³⁺ structure, and the microcrystal changed from hexahedron to tetrahedron with increasing Eu³⁺ doping concentration. It was found that the final product of NaLu_1–<i>x</i>Eu_<i>x</i>(WO₄)₂ (<i>x</i> ≥ 0.4) can not be obtained directly, intermediated by WO₃, Na₂W₂O₇, and REO­(OH). The photoluminescence and electroluminescence properties were also investigated. Because of an intense red emission and a good excitation in the region of near-ultraviolet (n-UV), the samples NaLu­(WO₄)₂:Eu³⁺ can be served as alternative red phosphors in the n-UV chip-based LED application

Structure Refinement and Two-Center Luminescence of Ca₃La₃(BO₃)₅:Ce³⁺ under VUV–UV Excitation

A series of Ca₃La_{3(1–<i>x</i>)}Ce_3<i>x</i>(BO₃)₅ phosphors were prepared by a high-temperature solid-state reaction technique. Rietveld refinement was performed using the powder X-ray diffraction (XRD) data, which shows occupation of Ce³⁺ on both Ca²⁺ and La³⁺ sites with a preferred location on the La³⁺ site over the Ca²⁺ site. The prepared samples contain minor second phase LaBO₃ with contents of ∼0.64–3.27 wt % from the Rietveld analysis. LaBO₃:1%Ce³⁺ was prepared as a single phase material and its excitation and emission bands were determined for identifying the influence of impurity LaBO₃:Ce³⁺ luminescence on the spectra of the Ca₃La_{3(1–<i>x</i>)}Ce_3<i>x</i>(BO₃)₅ samples. The luminescence properties of Ca₃La_{3(1–<i>x</i>)}Ce_3<i>x</i>(BO₃)₅ samples under vacuum ultraviolet (VUV) and UV excitation were investigated, which exhibited two-center luminescence of Ce³⁺, assigned to the Ce(1)³⁺ center in the La³⁺ site and Ce(2)³⁺ center in the Ca²⁺ site, taking into account the spectroscopic properties and the Rietveld refinement results. The influences of the doping concentration and the excitation wavelength on the luminescence of Ce³⁺ in Ca₃La_{3(1–<i>x</i>)}Ce_3<i>x</i>(BO₃)₅ are discussed together with the decay characteristics

Structure Refinement and Two-Center Luminescence of Ca₃La₃(BO₃)₅:Ce³⁺ under VUV–UV Excitation

A series of Ca₃La_{3(1–<i>x</i>)}Ce_3<i>x</i>(BO₃)₅ phosphors were prepared by a high-temperature solid-state reaction technique. Rietveld refinement was performed using the powder X-ray diffraction (XRD) data, which shows occupation of Ce³⁺ on both Ca²⁺ and La³⁺ sites with a preferred location on the La³⁺ site over the Ca²⁺ site. The prepared samples contain minor second phase LaBO₃ with contents of ∼0.64–3.27 wt % from the Rietveld analysis. LaBO₃:1%Ce³⁺ was prepared as a single phase material and its excitation and emission bands were determined for identifying the influence of impurity LaBO₃:Ce³⁺ luminescence on the spectra of the Ca₃La_{3(1–<i>x</i>)}Ce_3<i>x</i>(BO₃)₅ samples. The luminescence properties of Ca₃La_{3(1–<i>x</i>)}Ce_3<i>x</i>(BO₃)₅ samples under vacuum ultraviolet (VUV) and UV excitation were investigated, which exhibited two-center luminescence of Ce³⁺, assigned to the Ce(1)³⁺ center in the La³⁺ site and Ce(2)³⁺ center in the Ca²⁺ site, taking into account the spectroscopic properties and the Rietveld refinement results. The influences of the doping concentration and the excitation wavelength on the luminescence of Ce³⁺ in Ca₃La_{3(1–<i>x</i>)}Ce_3<i>x</i>(BO₃)₅ are discussed together with the decay characteristics

The Influence of Oxygen Vacancies on Luminescence Properties of Na₃LuSi₃O₉:Ce³⁺

Oxygen vacancies play an important role in the luminescence processes of inorganic scintillator materials. In order to study the effects of oxygen vacancies on the luminescence properties of Na₃LuSi₃O₉:Ce³⁺, these phosphors were prepared using a high temperature solid-state reaction method under different atmosphere and raw materials. It was found that oxygen vacancy had great influence on the absorption, photoluminescence and decay curves of Na₃LuSi₃O₉:Ce³⁺. The luminescence intensity and peak position showed a regular change when synthesizing atmosphere changed. Na₃LuSi₃O₉:Ce³⁺ with more oxygen vacancies showed much stronger luminescence intensity at high temperature than that without vacancies. And it was also found that the decreasing of oxygen vacancies can quicken the photoluminescence decay of Ce³⁺ in Na₃LuSi₃O₉. The existence of oxygen vacancies in Na₃LuSi₃O₉:Ce³⁺ was confirmed by Zr⁴⁺ doping and thermoluminescence emission spectra. At last, emission bands of Ce³⁺ and oxygen vacancies were well distinguished under X-ray excitation and probable cause of the formation of oxygen vacancies was discussed