Luminescence properties of terbium-, cerium-, or europium-doped α-sialon materials

New interesting luminescent α-sialon (M(m/val+)val+ Si12-(m+n) Al(m +n)OnN(16-n)) (M = Ca, Y) materials doped with Ce, Tb, or Eu have been prepared and their luminescence properties studied. These show that Tb and Ce are in the 3+ and Eu in the 2+ state. Low-energy 4f↔5d transitions are observed as compared to the luminescence of these ions doped in oxidic host-lattices. This is partially explained by the nitrogen-rich coordination of the rare-earth ion and partially by the narrow size of the lattice site. The latter gives rise to a strong crystalfield splitting of the 5d band and a rather large Stokes shift for Ce3+ and Eu2+ (6500-7500 and 7000-8000 cm-1, respectively). For (Y,Tb)-α-sialon the Tb3+ 4f↔5d excitation band (∼260 nm) is in the low-energy host-lattice absorption band (≤290 nm), giving rise to a strong absorption for 254-nm excitation, but a low quantum efficiency. The latter is due to photoionization processes or selective excitation of Tb3+ at the defect-rich surface, resulting in radiationless transitions. Ce- and Eu-doped Ca-α-sialon show bright long-wavelength luminescence (maxima at 515-540 and 560-580 nm for Ce and Eu, respectively) with a high quantum efficiency and high absorption for 365- and 254-nm excitation. The Eu2+ emission intensity and absorption increases for increasing m, which is explained by the Eu2+ richer α-sialon composition. The position of the Eu2+ emission does not shift with changing composition of the host-lattice (m, n values), indicating that the local coordination of the Eu2+ ion is hardly dependent on the matrix composition. © 2002 Elsevier Science (USA).