Rare Earth Calcium Tungstate

Nano calcium tungstate is very promising is a promising self luminescent fluorescent material. It can emit dazzling light without being modified, thus playing an important role in the X ray, electron beam and ultraviolet ray and other optical fields.

In recent years, doping a small amount of rare earth ions in calcium tungstate has become a research trend. Scholars have found that phosphor with three primary colors can be synthetised by doping rare earth ions, greatly increasing the luminous range of calcium tungstate. The major doped rare earth ions are europium, Eu³⁺, terbium, Tb³⁺, dysprosium, Dy³⁺ and samarium Sm³⁺. Calcium tungstate can achieve different color effects by doping different rare earth ions. Additionally, its luminous intensity can be improved by controlling the pattern and size.

Current preparation methods of rare earth calcium tungstate including coprecipitation method, hydrothermal / solvothermal synthesis, high temperature solid phase method, ultrasonic chemical method, microwave method and molten-salt growth method. Among them, hydrothermal / solvothermal synthesis is widely used, because its synthesis of rare earth ions doped CaWO₄ phosphor has many advantages such as low reaction temperature, neat morphology and relatively uniform particle size.

In solvothermal synthesis, scholars tested respectively four rare earth elements, namely terbium oxide, europium oxide, samarium oxide and dysprosium oxide. A mixture of water and ethylenediamine with a volume ratio of 1 to 2 was used as solvent. And the precursor was obtained at a reaction temperature of 160 ℃ and a reaction time of 24 h. When the precursor is calcined at 800 ℃, the rare earth doped CaWO₄ nanocrystals with tetragonal structure can be obtained.

When the excitation wavelength is 254 nm, CaWO₄:Tb³⁺ has a strong emission peak near 544 nm. CaWO₄ radical phosphor with different color light is obtained by doping different rare earth ions. CaWO₄:Eu³⁺ red light, CaWO₄:Dy³⁺ blue light, CaWO₄:Sm³⁺ red light, CaWO₄:Tb³⁺ strong green light.

By the above method, after adding rare earth, calcium tungstate has been issued red, blue, green (RGB) three primary colors. We know that red, blue, and green can blend all the colors of an electronic display, which is also the basis of LED display technology.

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