Luminescence and EnergyTransfer in Lu3Al5O12ScintillatorsCo-Doped with Ce3橷 Tb3.

Lu3Al5O12(LuAG) dopedwith Ce3 a promising scintillator material with a highdensityand a fast response time. The light output under X-ray or γ-rayexcitation is, however, well below the theoretical limit. In thispaper the influence of codoping with Tb3 investigatedwith the aim to increase the light output. High resolution spectraof singly doped LuAG (with Ce3 Tb3) arereported and provide insight into the energy level structure of thetwo ions in LuAG. For Ce3췪phonon lines and vibronicstructure are observed for the two lowest energy 5d bands and theStokes’ shift (2 350 cm–1) and Huang–Rhyscoupling parameter (S= 9) have been determined.Tb3–5d transitions to the high spin (HS) andlow spin (LS) states are observed (including a zero-phonon line andvibrational structure for the high spin state). The HS–LS splittingof 5400 cm–1is smaller than usually observed andis explained by a reduction of the 5d–4f exchange couplingparameter Jby covalency. Upon replacing the smallerLu3誉 with the larger Tb3誉, the crystalfield splitting for the lowest 5d states increases, causing the lowest5d state to shift below the 5D4state of Tb3橷 allowing for efficient energy transfer from Tb3 Ce3皌 to the lowest temperatures. Luminescencedecay measurements confirm efficient energy transfer from Tb3 Ce3橷 provide a qualitative understanding of theenergy transfer process. Co-doping with Tb3皇 not resultin the desired increase in light output, and an explanation basedon electron trapping in defects is discussed. [ABSTRACT FROM AUTHOR]