The variation with charge gain of the total number of photons emitted per e
lectron, in the visible and near-infrared (NIR) regions (400 < lambda < 100
0 mn), in Ar/CF4 mixtures, is investigated for CF4 concentrations below 15%
. Measurements were performed in a uniform field configuration and results
are presented for charge gains below 100, under X-ray excitation. The maxim
um number of photons emitted per drifting electron (0.7 and 0.2 ph/e(-) for
Ar + 2% CF4 and Ar + 10% CF4, respectively) is obtained for a charge gain
G similar to 4. The spectral distribution of the emitted light in Ar/CF4 mi
xtures is also analyzed. The pressure dependence (1-4 atm) of the secondary
light output, in the visible and near infrared regions is studied as a fun
ction of the reduced electric field E/P for pure argon and Ar/CF4 mixtures.
Above the charge multiplication threshold, the maximum number of photons e
mitted per electron decreases by a factor of about 1.5 when the pressure in
creases from 1 to 2 atms.