Which cheap IR LEDs and Sensors are out there for arduino?

I am planning to play around with different IR LEDs and sensors. Basically I want to emit different IR wave lengths through different samples (lets say a banana or any object) and measure on the other side the absorption with an appropriate sensor.

There are a lot of ~940nm IR LEDs commercially available and IR sensors like the popular TSL235R sensor (it's very cheap) that detects any light in the range of 300-1000nm. This is a good start, but I am actually looking for LEDs and sensors that can emit/detect in the range of 5-10 µm (mid-IR). I was not able to find any good LED/sensor pair that works at this range. So I am asking you guys if you know about any other cheap LEDs/sensors that I can test. Thanks.

Browse around at Digikey.com http://www.digikey.com/product-search/en/optoelectronics/infrared-uv-visible-emitters/524328?k=led

Thanks, but unfortunately nothing on this list goes beyond 1720nm.

Spectrophotometry with opaque objects? Not so sure about that. Not sure what's influencing your choice of wavelengths, but a bulb that emits a known spectral output gives you reference points across many wavelengths. So the bulb is more of a shotgun approach, while the sensor is what you dial in to which wavelength you want to see the differences in. I.e., you should focus on a capable sensor because the bulb is the least of your concerns.

yes a bulb that emits a wide spectral output is ok, but I feel like the mid-IR sensors didn't hit the commercial market yet. There are some companys out there that sell them in the range of 1-4.7µm but you have to request a quote so I guess these sensors are probably expensive right now.

What about this one (Operating wavelength 7-14μm)? Could I possibly abuse this as a detector...?

http://www.aliexpress.com/item/Free-Shipping-RE200B-PIR-Human-Infrared-Radial-Sensor-RE200B-dual-pyroelectric-infrared-sensor-30730/32490940059.html