Everything about Pbs totally explained
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Lead sulfide (also spelled
sulphide, see
Sulfur#Spelling) is a
chemical compound, most often purified from the
mineral galena. PbS,
PbSe and
PbTe lead salts are
semiconductors of the IV-VI family. Lead sulfide is toxic due to the lead content, see
lead poisoning.
Applications
Lead sulfide and several other
lead compounds are used as detection element material in various
infra-red sensors. Of these,
PbS (lead
sulfide) is one of the oldest and most commonly used. It is used for eg.
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
room temperature, PbS elements are sensitive to radiation at
wavelengths between approximately 1 and 2.5
μm. This range corresponds to the shorter wavelengths in the IR
band, and is called near-IR, a term which refers to the fact that it's close to the wavelengths of
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
silicon,
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 isn't 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
bismuth sulfide and
tellurium.
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