Codoping of LSO:Ce with Yb³⁺ and Dy³⁺ ions

Nowadays, doped oxide crystals are successfully used as luminescent materials in laser and scintillation systems and medical diagnostic devises. Such crystals exhibit high chemical and radiation stability and wide transparency range. Cerium-doped rare-earth oxyorthosilicates, in particular, Lu₂SiO₅:Ce³⁺ (LSO:Ce) stand out in the doped oxide crystal family. This scintillator is used mainly in modern positron emission tomographs. However, LSO:Ce crystal reveals undesirable for scintillator effect, an effective energy storage, that can be observed as an afterglow or thermoluminescence.
It was shown that a high afterglow level of LSO:Ce is caused by the effective charging of electron traps. Due to the fact that the lowest excited 5d level of Ce³⁺ ion is located close to the bottom of the conduction band, the dopant ion can undergo ionization, and transport of electrons to trapping centers occurs through the conduction band.
Since doped rare-earth ions and electron traps in a LSO:Ce crystal are independent subsystems, one can affect the energy storage efficiency by crystal co-doping with other rare-earth elements, which possess strongly pronounced donor or acceptor properties regarding charge carriers. Co-doping can promote the enhancement of the charge carrier recombination process, which rivals with the trapping one, or, conversely, reduce the recombination rate.

Our results:
The incorporation of the co-dopant ions with the different donor-acceptor properties to charge carriers significantly affects the charge interactions in Lu₂SiO₅:Ce³⁺ crystal, and allows the efficiency of energy storage to be controlled. According to the proposed mechanisms of free charge carriers recombination in LSO:Ce,Dy и LSO:Ce,Yb crystals, the Dy³⁺ ions act as a hole trap and promote the increase of the energy storage effect; Yb³⁺ ions are acceptors of electrons and produce the additional channel of charge carrier recombination that reduces the energy storage level in LSО:Ce,Yb. So we can see an increase of thermoluminescence level for LSO:Ce,Dy crystals and reduction of thermoluminescence level for LSО:Ce,Yb crystals.

Main publications:

• Masalov, A.; Vyagin, O.; Ganina, I.; Malyukin, Yu.; Zenya, I.; Starzhinskii, N. Effect of coactivation with Dy³⁺ and Yb³⁺ ions on the efficiency of energy storage in Lu₂SiO₅:Ce³⁺ crystals// Technical Physics Letters 35 (2), 2009, 154-157(4) abstract
• N. V. Znamenski, E. A. Manykina, E. A. Petrenko, T. G. Yukina, Yu. V. Malyukin, P. N. Zhmurin, B. V. Grinev, A. A. Masalov and A. P. Shpak. The Nature and Mechanism of Charging of Electron Traps in Lu₂SiO₅: Ce³⁺ Crystals// JETP – 2004. – v.99.,№ 2. – P.386–393. abstract
  

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