The aim of the work was to study the nature of unstable luminescence of nitride bulk layers and heterostructures under stationery electron beam irradiation. During irradiation increasing of intensity of luminescence was observed. Typical times of this effect are tens up to hundreds of seconds. Details of the effect were studied. It was noticed that in several cases the irradiated by electron beam area was characterized by different luminescence properties even after 24 h at room temperature in vacuum. Several mechanisms leading to increasing of the intensity of luminescence were discussed.