Zinc Sulfide

Material
ZnS


Zinc Sulfide is an IR window material and a transparent semiconductor with a large direct band gap. It also possesses piezoelectric, photoconductive and electroluminescent properties. Zinc Sulfide is produced by a Chemical Vapor Deposition process (CVD).

Two grades of ZnS are available:

Regular (FLIR) grade Zinc Sulfide is a polycrystalline optical material and has reasonable hardness. FLIR grade ZnS has yellow colour and is translucent in the visible range. It is used as it is deposited without any further treatment. The material is often used for IR windows and lenses in the thermal band (8 to 14 µm) as a tough front optic in thermal imaging systems, particularly those subjected to harsh environments.

Multispectral grade Zinc Sulfide is treated after growth with a special process to eliminate microscopic voids and defects which occur in the regular grade material. This extends the transmission with low absorption and scatter to include visible region to infrared range. Clear grade ZnS is used for Multispectral applications as external windows or domes that require a single aperture or beam path for several wavebands like systems they have a visible camera, a mid- and long-wave detector and a laser rangefinder.

Properties
Optical Properties FLIR ZnS Multispectral ZnS
Transmission range in µm @10% min. 1 - 14 0.35 - 13
Transmission range in µm @50% min. 1 - 13 0.37 - 13
Refractive index 2.192 @10.6µm 2.20084 @10µm
Reflection losses in % at 1 surface 14 @10µm 14 @10µm
Reflection losses in % at 2 surfaces 24.6 @10.6µm 24.7 @10.6µm
dn/dT in 1/K 43 · 10-6 @3.39µm 38.7 · 10-6 @3.39µm
Physical Properties FLIR ZnS Multispectral ZnS
Density in g/cm³ 4.08 4.09
Melting point in °C 1827 1827
Specific heat capacity in J/(kg · K) 469 515
Thermal Conductivity in W/(m · K) 16.7 @296K 27.2 @298K
Thermal Expansion in 1/K 6.6 · 10-6 @273K 6.5 · 10-6 @273K
Dielectric constant 8.393 88
Solubility in water in g/100g unsoluble unsoluble
Mohs hardness 3.5 - 4
Knoop hardness in kg/mm² 160 160
Material type Polycrystalline, synthetic Polycrystalline, synthetic
Crystal type cubic, Zincblende structure
Crystal structure F43m F42m
Lattice constant in Å a = 5.67
Elastic coeficients in GPa C11 = 102
C12 = 64.6
C44 = 44.6
Young's Modulus (E) in GPa 87.6 33
Shear Modulus (G) in GPa 80.41
Bulk Modulus (K) in GPa 63.1
Rupture Modulus in MPa 68.9
Apparent elastic limit in MPa 103.4 68.9
Poisson ratio 0.29 0.28
Spectral Properties