title: Luminescence and energy transfer in Lu3Al5O12 scintillators co-doped with Ce3+ and Tb3+.
abstract: Lu(3)Al(5)O(12) (LuAG) doped with Ce(3+) is a promising scintillator material with a high density and a fast response time. The light output under X-ray or γ-ray excitation is, however, well below the theoretical limit. In this paper the influence of codoping with Tb(3+) is investigated with the aim to increase the light output. High resolution spectra of singly doped LuAG (with Ce(3+) or Tb(3+)) are reported and provide insight into the energy level structure of the two ions in LuAG. For Ce(3+) zero-phonon lines and vibronic structure are observed for the two lowest energy 5d bands and the Stokes' shift (2 350 cm(-1)) and Huang-Rhys coupling parameter (S = 9) have been determined. Tb(3+) 4f-5d transitions to the high spin (HS) and low spin (LS) states are observed (including a zero-phonon line and vibrational structure for the high spin state). The HS-LS splitting of 5400 cm(-1) is smaller than usually observed and is explained by a reduction of the 5d-4f exchange coupling parameter J by covalency. Upon replacing the smaller Lu(3+) ion with the larger Tb(3+) ion, the crystal field splitting for the lowest 5d states increases, causing the lowest 5d state to shift below the (5)D(4) state of Tb(3+) and allowing for efficient energy transfer from Tb(3+) to Ce(3+) down to the lowest temperatures. Luminescence decay measurements confirm efficient energy transfer from Tb(3+) to Ce(3+) and provide a qualitative understanding of the energy transfer process. Co-doping with Tb(3+) does not result in the desired increase in light output, and an explanation based on electron trapping in defects is discussed.
authors: CMI, Debye Institute for Nanomaterials Science, Utrecht University, P O. Box 80 000, 3508 TA Utrecht, The Netherlands.
authors: Joanna M
authors: JM
authors: Ogiegło
authors: Aleksander
authors: A
authors: Zych
authors: Konstantin V
authors: KV
authors: Ivanovskikh
authors: Thomas
authors: T
authors: Jüstel
authors: Cees R
authors: CR
authors: Ronda
authors: Andries
authors: A
authors: Meijerink
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D002563:Cerium / Q000737:chemistry*; D004735:Energy Transfer; D049449:Luminescence; D008163:Luminescent Measurements; D008187:Lutetium / Q000737:chemistry*; D013725:Terbium / Q000737:chemistry*
chemical_list: D013725:Terbium; D002563:Cerium; D008187:Lutetium; D000537:Aluminum Oxide