What is an infrared emitter, infrared light emitting diode, detector circuit

850 nm 80 uA 2 nA 60 deg Surface Mount Silicon PIN Photodiode – DIL-SMT-2 Website URL: https://www.futureelectronics.com/p/semiconductors–optoelectronics–infrared-emitters-detectors/q65110a1209-ams-osram-1170755 Country List: Bangladesh