Zinc sulfide

Zinc sulfide

Zinc sulfide (or zinc sulphide) is a chemical compound with the formula ZnS. Zinc sulfide is a white- to yellow-colored powder or crystal. It is typically encountered in the more stable cubic form, known also as zinc blende or sphalerite. The hexagonal form is also known both as a synthetic material and as the mineral wurtzite. Tetragonal form is also known as very rare mineral polhemusite (Zn,Hg)S. Both sphalerite and wurtzite are intrinsic, wide-bandgap semiconductors. The cubic form has a band gap of 3.54 eV at 300 K whereas the hexagonal form has a band gap of 3.91 eV.

A transition from the sphalerite form to the wurtzite form occurs at around 1293.15 K. Sphalerite melts at 1991 K. It has a standard enthalpy of formation of −204.6 kJ mol−1 at 298 K.

Applications

ZnS was used by Ernest Rutherford and others in the early years of nuclear physics as a scintillation detector, because it emits light on excitation by x-rays or electron beam, making it useful for x-ray screens and cathode ray tubes. It also exhibits phosphorescence due to impurities on illumination with blue or ultraviolet light.

Zinc sulfide, with addition of few ppm of suitable activator, is used as phosphor in many applications, from cathode ray tubes through x-ray screens to glow in the dark products. When silver is used as activator, the resulting color is bright blue, with maximum at 450 nm. Manganese yields an orange-red color at around 590 nm. Copper provides long glow time and the familiar glow-in-the-dark greenish color. Copper doped zinc sulfide (ZnS+Cu) is used also in electroluminescent panels.

Zinc sulfide is also used as an infrared optical material, transmitting from visible wavelengths to over 12 micrometres. It can be used planar as an optical window or shaped into a lens. It is made as microcrystalline sheets by the synthesis from H2S gas and zinc vapour and sold as FLIR (Forward Looking IR) grade ZnS a pale milky yellow visibly opaque form. This material when hot isostatically pressed (HIPed) can be converted to a water-clear form known as Cleartran (trademark). Early commercial forms were marketed as Irtran-2 but this designation is now obsolete.

It can be doped as both n-type semiconductor and p-type semiconductor, which is unusual for the II-VI semiconductors. ZnS is a covalently bonded solid.

Production in lab

It is easily produced by mixing an amount of zinc and sulfur and then igniting it. The result (after cooling) is zinc sulfide.

See also

References

External links

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