PSI - Issue 47

Stavros Tseremoglou et al. / Procedia Structural Integrity 47 (2023) 119–124 Tseremoglou/ Structural Integrity Procedia 00 (2023) 000 – 000

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the band gap of La. The 5d electron is probably bound to a Ce 3+ trapped exciton and its return to the ground state of Ce 3+ occurs without light emission (Dorenbos 2005). According to another possible explanation for the LY reduction, a Ce 3+ cation in the excited state does not have exactly the same position in the crystal lattice as in the ground state, resulting in a cross-over between them in the configurational coordinate diagram. This displacement is due to change of the average distance of Ce 3+ from adjacent ions at the excited state. With temperature increase, the 5d excited electron receives the required energy to reach the cross-over point and return to the ground state 4f without radiation emission (Blasse et al. 1994). 4. Conclusions In the current study, the absolute luminescence efficiency of a LaCl 3 :Ce crystal was investigated, within a range of temperatures. 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