A simple collisional–radiative model for low-pressure argon–oxygen mixture discharges

The simple collisional–radiative model is investigated in low-pressure discharges containing argon and oxygen. Using this model, one can obtain a simple relationship between the electron density and the intensity ratio of two argon emission lines without knowing electron temperature. It is found that the relationship is valid in these discharges regardless of oxygen concentration, if argon np levels with zero total angle momentum quantum numbers are selected. This is because that the kinetics of these levels is not significantly affected by the metastables under low-pressure conditions. The application and validity of this model in other kinds of low-pressure plasmas, such as discharges contain CF₄, are also discussed.