Dy-alpha-sialon and beta-Si3N4 materials containing Dy-oxynitride glass were hot pressed at 1800 degrees C for 1 h. The luminescence spectra of Dy3+ in these samples were compared when excited at 350 nm. The results showed that two strong emission bands in the region 470-500 nm and 570-600 nm, associated with the F-4(9/2)->H-6(15/2) and F-4(9/2)->H-6(13/2) transitions of Dy3+ ions, were observed in Dy-alpha-sialon. However, no emission peak was detected from the beta-Si3N4 sample, despite it containing the same amount of Dy3+ cations. This proved that only the Dy3+ cations in the alpha-sialon structure, not those in the oxynitride glass, produce the luminescence spectrum.