I suppose you mean He instead of Ne and F2 instead of F. Efficient gas mixture content can depend on pumping procedure, let say e-beam pumped or electric discharge laser. For instance,1.2% Kr and 0.07% F2 in He is all right for electric discharge one.
If you work with an excimer laser, I would strongly recommend to read 'Excimer lasers" ed. by Ch.K.Rhodes, Springer-Verlag, Berlin, Heidelberg, New York (1979)
Active medium : is a mixture of a noble gas, halogen gas and a buffer gas, usually neon. Gas mixture in a typical excimerlaser consists of 2–9% of a noble gas, 0.2% of a halogen gas, and 90–98% of a buffer gas which serves as a medium to transport energy. The mixture is confined in a pressure vessel, typically at a pressure of 3500–5000 millibars. The gas mixture is usually excited by means of a fast electric discharge lasting a few tens of nanoseconds