The role of Ce3+ Co-doping in the luminescent enhancement of Bi3+ emission and Bi3+→Bi2+ conversion in LiLaP4O12 host

Abstract

This work investigates the luminescent versatility of the LiLa_(1-x-y)Bi_xCe_yP₄O₁₂ system as a scintillator material capable of displaying emission in a range from the blue to the red region depending on the Ce³⁺ concentration. The LiLaP₄O₁₂ host has been proven to be useful as a scintillator material when doped with some rare earths and with bismuth ions. However, the process of bismuth valence change induced by X-rays, when inserted in the LiLaP₄O₁₂ matrix, is not known to date, as well as whether this can be controlled and used to enhance the luminescence emission. To determine the mechanism of interaction between the Ce³⁺ and Bi³⁺ ions in the LiLaP₄O₁₂ host, doped and co-doped samples were synthesized and investigated. Identification of crystalline phase was carried out with X-Ray Powder Diffraction. The luminescent properties were studied via photoluminescence emission and excitation using synchrotron radiation. Scintillator features were studied through radioluminescence emission spectrum. The results indicate that Ce³⁺ transfers either energy or electrons to Bi³⁺ when excited with UV (5.2 eV) or X-rays, respectively. In the first case, the overall white luminescence is improved, while in the latter, enhanced red luminescence from Bi²⁺ was observed, indicating the valence change of Bi ions, assisted by Ce co-dopant. A luminescent mechanism, based on the vacuum-referred binding energy model applied to the experimental data, was proposed to explain the Bi²⁺ emission, deepening the understanding of the Bi emission mechanism and opening the possibility of tailoring the Bi²⁺/Bi³⁺ proportion varying the Ce-co-doping concentration.