Enhanced luminescence of oxygen atoms in solid molecular nitrogen nanoclusters

We studied luminescence accompanied an injection of the nitrogen-helium gas mixture after passing discharge into dense cold helium gas. Initially, when the experimental beaker was filled with superfluid helium and the nitrogen-helium gas was injected into bulk superfluid helium at T approximate to 1.5 K, the dominant band in the emission spectra was the alpha-group of nitrogen atoms. At these conditions, the nanoclusters of molecular nitrogen with high concentrations of stabilized nitrogen atoms were formed. When superfluid helium was evaporated from the beaker and the temperature at the bottom of the beaker was increased to T approximate to 20 K, we observed a drastic change in the luminescence spectra. The beta-group of oxygen atoms was dominated in the luminescence spectra, and the emission of the alpha-group became small. At high temperatures (T approximate to 20 K), most of the nitrogen atoms recombine on the surface of N-2 nanoclusters with the formation of excited nitrogen molecules. We explained the effect of the enhancement of beta-group emission by effective energy transfer from excited nitrogen molecules to the stabilized impurity oxygen atom inside N2 nanoclusters.