The infrared detector (or receiver) I used in this prototype is shown in the following image (actually, the receiver is the device with the red dot; the other one is just a transmitter that we're not using here).
The devices can be purchased at the following link (or by surfing the Internet): http://www.cosino.io/product/infrared-emitter-detector.
The datasheet is available at https://www.sparkfun.com/datasheets/Components/LTR-301.pdf.
Note that the image shows the topmost part only of the infrared devices. In reality, they look similar to a normal diode.