IrLED vs Photointerrupter
An infrared LED (IrLED) is a photoelectric conversion element that converts electrical energy into optical energy, with an emission wavelength between 800nm to 950nm.
Materials used include GaAs and GaAlAs.
Since photointerrupters (or phototransistors) combine a photodiode and transistor, the base current of the transistor is input as light. Silicon with a sensitivity between 400nm and 1100nm is used.