The role of zinc sulfide

Metal sulfides have excellent electrical properties and are widely used in semiconductors, pigments, photoluminescent devices, solar cells, infrared detectors, optical fiber communications, etc. Among them, zinc sulfide is one of the most widely studied and applied materials in II-VI compounds. So what is the role of zinc sulfide?

Zinc sulfide is a white to grayish white or light yellow powder. The color becomes darker when exposed to light. It is stable in dry air and gradually oxidizes to zinc sulfate when placed in moist air or with moisture for a long time. It is soluble in dilute inorganic acids, insoluble in water and alkaline solutions. The relative density is 3.98 (α type), (d25) 4.102 (β type), and it is irritating. Due to its many excellent properties, it is widely used in many fields.

1 Chemical Industry

Zinc sulfide is mainly used in paints and plastics in chemical production. The production of zinc sulfide was first recorded in France in 1783. It has become an important pigment in paints due to its white opacity and insolubility in water, organic solvents, weak acids, and weak bases. Zinc sulfide has now become the second most important pigment in the United States after titanium dioxide, but it continues to enjoy an important position in the European industry. As a bulk material, the melting point of commercial grade zinc sulfide is 1650℃, the purity is 98%, the Mohs hardness is 3.0, and the refractive index is 2.37. Due to its high refractive index and wear resistance, zinc sulfide pigment has a relatively high hiding power when applied in a thin layer on equipment, wax paper, and metal plates. Zinc sulfide is easy to disperse and not easy to agglomerate. It is neutral white and has good optical properties. It is often used as a component of thermosetting plastics, thermoplastics, reinforced fiberglass, flame retardants, artificial rubber and dispersants.

Zinc sulfide is very soft and therefore has little wear. The soles produced by white elastomers as pigments have a much longer service life than those made with TiO2.

As a stabilizer, zinc sulfide has also been inventively used in some thermoplastics, especially PP and PBT, to improve the thermal stability of polymers. As for the mechanism, there is no conclusive explanation so far. But we believe that it is because zinc sulfide can react with most metal ions with catalytic effects to form immobile complexes, avoiding the catalytic degradation caused by these ions entering the polymer lattice, which is the so-called "fixing effect" of zinc sulfide.

In addition, the softness of zinc sulfide gives it an unmatched advantage over TiO2 in processes requiring wear resistance.

2 Ceramics

Zinc sulfide is used in ceramics because it has good sintering properties. Studies have shown that the sintering properties of monodisperse zinc sulfide powder are higher than those of agglomerated zinc sulfide, and the sintering properties increase with decreasing particle size. The density of zinc sulfide ceramics obtained by sintering zinc sulfide with a particle size of 0.1 μm at 1000°C for 2 hours is as high as 98% of the theoretical density.

3 Optoelectronics

Cubic zinc sulfide has a high refractive index in the visible light range (n488: 2.43, n589=2.36) and does not absorb light in this band. Zinc sulfide is a wide bandgap semiconductor. The bandgap of the bulk material is 3.75eV, and the bandgap of 3nm zinc sulfide particles is 4.13eV, which is obviously blue-shifted. It is a potential photon material. In 1994, Bhargava R N first reported that a certain amount of manganese was doped into the semiconductor nanocrystalline material zinc sulfide to obtain doped nanocrystalline material zinc sulfide: manganese. By doping, the electron transition path in the luminescent body is changed, thereby reducing the non-radiative electron loss. Luminescence tests show that its quantum efficiency is greatly improved, and the decay time is shortened by 5 orders of magnitude compared with the bulk material, so that the zinc sulfide: manganese luminescent body has fast response and low threshold optical properties. Through the doping of other metal ions M (transition metal ions copper, silver, rare earth element ions samarium, europium, terbium, erbium, etc.), it was found that different dopants introduced into the nano zinc sulfide matrix can obtain visible emission in different bands. The color of electroluminescent display based on zinc sulfide varies with the added substances. For example, zinc sulfide doped with manganese (adding manganese fluoride, the luminescent wavelength is 675nm) is yellow-orange, doped with manganese and filter is yellow-green, doped with samarium is red, doped with terbium fluoride (adding terbium fluoride, the wavelength of 542.5nm and 487.5nm light) is green, and doped with thulium fluoride is blue. Erbium-doped zinc sulfide thin film devices have electroluminescent near-infrared luminescence performance. The presence of trace copper will cause the zinc sulfide structure in the local area to change from hexagonal crystal to cubic crystal, forming a variety of luminescent centers. Due to the existence of quantum size effect, the emission wavelength of nano zinc sulfide: M phosphor has also changed compared with the bulk phase. Therefore, the luminescent frequency, luminous efficiency, etc. can be modulated by doping and controlling the size of its particles to achieve doping at the molecular level, and it is expected to develop blue light-emitting devices to achieve ultra-high resolution and ultra-large screen display. The zinc sulfide: Mn, Cu DC electroluminescent material developed by Changchun Institute of Physics has reached the world's advanced level. It is used for digital, text, symbol and automatic analog display, computer terminal and radar display, large screen display, military, transportation, post and telecommunications, etc.

4 Photocatalysis

Since nano zinc sulfide is a photon material that can generate photon holes, the energy level change and energy gap widening brought about by the quantum size effect enhance its redox ability, making it an excellent photocatalytic semiconductor. Nano zinc sulfide is wrapped on polystyrene or silicon dioxide to form nanoparticles with a core-shell structure, and then the core is removed to make hollow balls, which float on the surface of wastewater containing organic matter, and the organic matter can be degraded by sunlight. The United States and Japan use this method to deal with pollution caused by offshore oil spills. This method can also be used to add powder to ceramic glazes to make them have the function of cleaning and sterilization, and can also be added to artificial fibers to make bactericidal fibers.

5 Infrared performance

Zinc sulfide is an infrared optical material with high infrared transmittance and excellent optical, mechanical and thermal comprehensive performance in the 3-5p.m and 8-12ym bands. It is a dual-band infrared observation window and hood material for aircraft. When using this property as a special absorbent material doped with pigments, a single particle with a larger particle size is required, and the metal nanolayer wrapped on the surface of zinc sulfide can be used for modification.

The excellent performance of zinc sulfide has been increasingly valued by materials scientists, and people have been exploring good synthesis methods to stabilize particles and control the size of particles from a microscopic perspective. With the continuous deepening of research work, there is hope to find low-dimensional zinc sulfide materials with uniform scale and shape and excellent optical, electrical and other properties in the future.