2020年2月17日星期一

Scintillation Crystal Material -- Magnesium Tungstate

When the inorganic crystal is subjected to high-energy particles or high-energy rays (such as X-rays, gamma-rays), a phosphor that emits visible light due to excitation of particles or rays, which is a scintillation crystal, and magnesium tungstate is a scintillation crystal.

Magnesium tungstate (MgWO4) single crystal belongs to the wolframite structure, its melting point is 1358 °C. The crystal has a wide emission band of blue white light with a peak value between 480~500 and nm, in which the half width of the spectrum reaches 140nm, the luminescent intensity of magnesium tungstate is sensitive to impurities and excessive grinding, and the emission intensity of the scintillation crystal is weakened regardless of the substance.

magnesium tungstate lamps image

The excitation spectrum of MgWO4 is wider than PbWO4. In early studies of scintillators, MgWO4 has the highest quantum efficiency, it is believed that the efficiency of converting 253.7 nm radiation to visible light is 100%. It is often used as reference samples of magnesium tungstate scintillator when measuring quantum efficiency. The subsequent results show that the actual quantum efficiency is about 85%. The current MgWO4 in the fluorescent lights and white lights have important applications, while quantum efficiency measurements are used as standard sample.

Method for preparing magnesium tungstate with high temperature solid state method and hydrothermal method. In general, the traditional high-temperature solid-state method is not only high calcination temperature, but also only monoclinic tungstate can be obtained. Co precipitation method can not prepare MgWO4 directly under normal temperature and atmospheric pressure. However, the scholars found that the hydrothermal method can obtain tetragonal magnesium tungstate at very low temperature, and less impurity phase formation, the rare earth ions can be doped into them, and can be converted to monoclinic phase at lower temperature, with good luminescence properties. Therefore, the hydrothermal method is more recommended by the method of preparation of magnesium tungstate.

It is often used for magnesium tungstate doped with Er3+, Nd3+, Tm3+, Ho3+, Yb3+ and other rare earth ions to produce near infrared luminescent materials, near infrared light has many special properties, such as large penetration depth, high intensity and light intensity absorbed, it has been widely used in optical fiber communication, laser source, biosensor and fluorescence immunoassay. In summary, the magnesium tungstate material also has great application potential.

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