Quantum level working of IR sensor.... There are datasheets of IR sensors like the TSOP1738 that conveniently tell me that when I make an IR LED flash at 38Khz, a current is produced. However, i would like to know what happens on an atomic level. Is it just a matter of electron promotion because of the infrared light ? Then how does the sensor only allow IR to cause excitation of the electrons ? Is it the material they use for these sensors that reacts only to the IR light ? How exactly does infrared light cause electrons to flow in this sensor ? I would be very grateful of anyone could either answer my question or point me to links where this is nicely explained. I need to know what is behind these sensors as I am researching IR communication and wish to know more about the sensing mechanism. Thank you.