Lead(II) sulfide

Lead sulfide (also spelled sulphide, see lead poisoning.

Applications

Lead sulfide and several other infrared detectors.

When used for infrared, these detection element are classified as photon detectors: unlike thermal detectors (the other major type), IR detectors respond directly to the incident radiation. Thermal detectors respond only to the material's temperature change caused by the energy from the photons. Because of this difference, radiation can then be measured in two ways, either by detecting the tiny photocurrent or by measuring the change in the materials electrical resistance. Measuring the resistance change is the more commonly used method.

At visible light. Only very hot objects emit radiation in these wavelengths.

Cooling the PbS elements, for example using pressurised or liquified gas or a Peltier element system shifts its sensitivity range to between approximately 2 and 4 μm. Objects which emit radiation in these wavelengths still have to be quite hot; several hundred degrees Celsius; but not as hot as those which are detectable by uncooled sensors.

Other compounds used for this purpose include indium antimonide (InSb) and HgCdTe, which have somewhat better properties for detecting the longer IR wavelengths.

The high dielectric constant of PbS leads to relatively slow detectors (compared to germanium, InSb or HgCdTe).

PbS can be formed as nanocrystals.

Astronomy

Elevations above 2.6 km (1.63 mi) on the planet Venus are coated with a shiny substance. Though the composition of this coat is not entirely certain, one theory is that Venus "snows" crystallized lead sulfide much as Earth snows frozen water. If this is the case, it would be the first time the substance was identified on a foreign planet. Other less likely candidates for Venus' "snow" are tellurium. [1]

See also

• infrared
• infra-red homing
• Lead(IV) Sulfide

References

• Lead Sulphide - An Intrinsic Semiconductor, E H Putley and J B Arthur, Proc. Phys. Soc. B, 64 pp. 616-618 (1951) doi:10.1088/0370-1301/64/7/110
• Absorption Spectra of Lead Sulphide at Different Temperatures, W. Paui and R. V. Jones, Proc. Phys. Soc. B, 6 (3) pp. 194-200 (1953).
• Electronic and Vibrational Properties of Lead Sulphide Nanocrystals, Janet Lynn Machol, Ph.D. Thesis, Cornell Univ. (1993).
• Nonlinear optical properties of lead sulfide nanocrystals in polymeric coatings, S W Lu et al, Nanotechnology 13 669-673 (2002) doi:10.1088/0957-4484/13/5/326