I have build a SF6 (and methane) camera some years ago.
I still have a SF6 narrow band-pass filter for this purpose (spectrogon BP-10500-775).
You have no chance to build a (passive) gascam with a simple bolometer, if you want to see small amounts of the gases.
You definitley need a cooled FPA for this, with very low noise.
Please remember, that you want to detect the photons, that are emitted from the gas itself. You can measure this only, if enough photon will reach your pixel.
With such a narrow bandpass you limit the spectrum a lot, but your bolometer furthermore measure all photons from the broad range, that the bolometer is sensitive at (i.e. 7.5 to 14 µm) and the band pass filter itself in front of your camera is NOT cooled, so it "heat" the FPA normally a lot more than the few photons from the gas you search for.
You have to detect nearly nothing on top of a huge radiator. Not possible with a uncooled detector.
Don't waste your time on this.
And PLEASE don't wast SF6 for such trials!
1kg of SF6 has an identical climate effect (Global warming potential) as 23500kg CO2 (23.5 metric tons of CO2!!).