PbS and PbSe infrared detectors for gas sensing

These detectors work because infrared radiation incident on the polycrystalline thin film promote electrons across the bandgap increasing the conductivity of the material in turn decreasing the resistance of the substance. 

The polycrystalline lead sulphide (PbS) units detect radiation in the wavelength range between 1 and 3.3 microns and exhibit a higher sensitivity than polycrystalline lead selenide (PbSe) which can detect radiation between 1 and 5.2 microns. These devices are photoconductive and require bias voltage to operate.

The detectors are manufactured in standard transistor style packages and have long expected lifetimes making them ideal for fit and forget applications such as gas sensing, surface inspection and identifying the presence of a flame. 

The PB25 is a collection of uncooled polycrystalline biased single element PbS detector with a 20% cut off at 3.3 microns and a maximum element size of 6x6mm².