I got a 38Khz 980nm IR receiver.
I want to use an IR transmitter that the receiver will not receive the transmitting IR signal or to receive the IR signal as little as possible.
Should I use an 36Khz 940nm emitter or an 38Khz 880nm instead?
Preferable for the minimum efficiency of the my receiver is to use an emitter with different wavelength or different frequency?
I wasn't aware that emitters had a pulse frequency. I though only receivers did. Do you know what these numbers represent? The 'frequency' is the pulse rate (how many times it turns on and off), the 'wavelength' is what part of the electromagnetic spectrum it is using. I put these in quotes because a wavelength is the reciprocal of a frequency and vice versa.
If you are going to be using these (transmitting/receiving) at the same time and you don't want to get into protocol complications, you want to have each (the 'wavelength' and the 'frequency') as far off each other as is possible. This will reduce as much as possible crosstalk between the two.
AFAIK, emitters are just IR LEDs, you have to pulse them at the correct frequency. There are libraries available for this, but you'll have to look for them yourself.
Try here: http://lmgtfy.com/?q=arduino+ir+transmitter+library
If you have multiple receivers controlled by one chip, you may find that they may interfere with each other depending on how the library is implemented. Depending on your usage, you may be able to get away with one transmitter and one receiver per unit using a communication protocol like I stated earlier. If you don't require too much data going across these two channels, you might be able to get away with it by writing your own library.