An IR photodiode can be used to detect IR light. It is commonly used in security cameras, it can also be found in IR proximity sensor or line follower sensor in combination with IR transmitter. The diode allows some current to flow through it which is proportional to the amount of IR light falling on it.
 
3mm Photodiode Features:
Fast response time
High Photo Sensitivity
Small Junction Capacitance
 
Applications:
Used to detect Light and its intensity
Used with IR LED for object detection, counting, encoder and more
Used in automatic door sensors
Used in line follower and object avoiding robot
Distinguish between Day and night
Automatic light (streetlight or vehicle light)  control
 
Note: This is a 3mm IR, but the colour of the LED might be different from what it appears on the picture. Some IR receivers like everlight PT204-6C also comes with white LED dom