Absorption, emission and excitation spectra of NO in N2 and mixed N2/Kr matrixes at various N2 concns. have been recorded by means of tunable synchrotron radiation and ArF laser excitation. The gas-to-matrix shifts, bandwidths and Stokes shifts of the lowest Rydberg level A2S+(v=0) level increase linearly with N2 concn. The blue-shift is attributed to modifications in the bulk properties of the crystals and not to local perturbations. In emission, the fluorescence from B2P(v= 0) and the phosphorescence from a 4P(v=0) are obsd. While the former is little affected by the presence of N2, the latter is strongly broadened and red-shifted. High-resoln. scans and lifetime measurements upon laser excitation support the existence of at least two classes of NO sites. [on SciFinder (R)]