Calcium Tungstate Self-Excited Phosphor Preparation

Calcium tungstate (CaWO₄) is a self-excited phosphor, which is an effective luminescent material under X-ray, electron and ultraviolet excitation. Blue fluorescence was observed under 253.7 nm ultraviolet irradiation. The peak wavelength of emission spectrum was 423 nm and the half width was 120 nm. It emits blue light under the excitation of cathode rays. Because of its excellent blue fluorescence, it has been widely used in luminescent coatings, fluorescent lamps, neon lights, X-ray fluorescent screens, scintillation counters and lasers.

The results show that the higher the purity of calcium tungstate is, the better its luminescent properties will be, and the more widely used it will be. However, because the calcium tungstate used now is mainly synthesized by artificial method, its luminescent properties are not good and its luminescent intensity is weak.

In view of the current technical situation, some scholars have put forward the technical proposal as follows: a preparation method of calcium tungstate phosphor, which is characterized by using cuttlefish bone as raw material and hydrothermal synthesis of fluorescent body, including the following steps:

Take the cuttlefish bones from the market, peel them, cut them into blocks and set aside. 12 mmol, 1.20 g block cuttlefish bone (CaCO₃), 1.0 mmol, 3.04 g ammonium tungstate (NH₄)₁₀O₄₁W₁₂, the ratio of cuttlefish bone to molar ammonium tungstate is 12:1, then placed in the PTFE reactor, added 15 ml distilled water, sealed, and reacted in the oven at 120 ℃ or 24 hours. After cooling to room temperature, flushing with distilled water, then calcining a small sample at 200, 600, 900 and 1000 degrees for 1 to 2 hours respectively, calcium tungstate phosphors were obtained.

The calcined samples were tested by infrared and fluorescence. Infrared spectra show that when calcined to 900 ℃, the product has a high purity, and the organic impurities in cuttlefish bones are basically burned off. Fluorescence analysis showed that the fluorescence intensity of the product increased gradually with the increase of calcination temperature. When calcined to 900 C, the product had a high fluorescence intensity at 414 nm, about 1093 a.u., under 240 nm light excitation.

Calcium carbonate in cuttlefish bone reacts fully with Ammonium Tungstate by hydrothermal reaction at high temperature and pressure. After calcination at high temperature, the organic impurities and other impurities in the product are removed. Calcium tungstate phosphors with good luminescent properties are obtained. Especially when ammonium tungstate can not fully participate in the reaction, they can be completely decomposed in the calcination process without introducing impurities. Therefore, it can be widely used in luminescent coatings, fluorescent lamps, neon lights, X-ray fluorescent screens and so on.

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