Luminescence Properties of Terbium-, Cerium-, or Europium-Doped α-Sialon Materials

✍ Scribed by J.W.H. van Krevel; J.W.T. van Rutten; H. Mandal; H.T. Hintzen; R. Metselaar

• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 201 KB
• Volume: 165
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2001.9484

✦ Synopsis

New interesting luminescent a-sialon (M (m/val+) val+ Si 12-(m+n) Al (m+n) O n N (16Àn) ) (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 hostlattices. 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 Ce 3+ and Eu 2+ (6500-7500 and 7000-8000 cm À1 , respectively). For (Y,Tb)-a-sialon the Tb 3+ 4f-5d excitation band (B260 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 Tb 3+ at the defect-rich surface, resulting in radiationless transitions. Ce-and Eu-doped Ca-a-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 Eu 2+ emission intensity and absorption increases for increasing m, which is explained by the Eu 2+ richer a-sialon composition. The position of the Eu 2+ emission does not shift with changing composition of the hostlattice (m, n values), indicating that the local coordination of the Eu 2+ ion is hardly dependent on the matrix composition. # 2002 Elsevier Science (USA)