Calculated microwave emission spectra for the O-N and P-N for small (i.e. N = 1 for O-N and P-N, black), large (i.e. N = 10 for O-N and P-N, blue) and medium-sized nanocluster containing ~20 atoms (N = 3 for O-N, N = 4 for P-N and N = 10 for SiO-N, red) under MC (T = 20 K) conditions. The emissivity is calculated using a fraction of 0.01 of Si in the medium and large nanoclusters and 1e-5 for the smallest nanoclusters.