We produced mixtures of N-2-O-2 with different concentrations and performed low-temperature Raman studies at ambient and high pressures. From spectra in vibron and phonon regions, we determined band frequency, bandwidth, and band intensity as a function of temperature, pressure, and concentration. We determined the vibron Raman cross-sections and deduced the true concentrations of mixtures from vibron Raman band intensities. These concentrations were different from those determined from partial gas pressure of the initial gaseous mixtures. From fingerprints in Raman spectra, such as jumps in band frequencies or additional band splitting, we were able to prove phase transitions and propose a preliminary T-x phase diagram. We compared this diagram with two reported in the literature from structural analysis. Comparing all three variants of the T-x phase diagrams we found several discrepancies and inconsistencies, which we associate with different solid sample production techniques. Since we could prove that our samples were in thermodynamic equilibrium, we are convinced that we improved the known phase diagram substantially. From Raman band intensities of the O-2 vibrations in different phases of N-2 and O-2, we were able to determine quantitatively the solubility of O-2 in N-2. Preliminary Raman studies of 2% and 7% O-2 in N-2 at high pressure and low temperatures showed that a larger amount of O-2 can be dissolved in N-2 than at ambient pressure. At the critical pressure (p similar to 15 GPa) we found from Raman spectra that O-2 is demixed from 7% O-2 in N-2 to form epsilon-O-2. This was previously called a "new phase" in the literature and not understood up to now. Finally, from band frequencies we determined the environmental shift of oxygen molecules in the mixture which is related to the intermolecular potential U(N-2-O-2) between different types of molecules.