Tuning scintillation properties of Lu2SiO5 by Ce and Ca codoping

The light-yield enhancement and decay-time shortening by Ca codoped with ${\mathrm{Lu}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$:Ce have been observed in experiment. However, the underlying mechanisms remain enigmatic. First-principles calculations are performed to gain insight into the effect of Ca codoping. We show that first, the formation of ${\mathrm{Ca}}_{\mathrm{Lu}}\phantom{\rule{4.pt}{0ex}}\text{\ensuremath{-}}\phantom{\rule{4.pt}{0ex}}{V}_{\mathrm{O}}$ complex defects is favored, which causes the dissociation of ${\mathrm{Ce}}_{\mathrm{Lu}}\phantom{\rule{4.pt}{0ex}}\text{\ensuremath{-}}\phantom{\rule{4.pt}{0ex}}{V}_{\mathrm{O}}$; therefore, the nonradiative decay of Ce via ${V}_{\mathrm{O}}$ is suppressed, leading to light-yield enhancement. Secondly, the downward shift of the Fermi level by the codoping effect causes the observation of ${\mathrm{Ce}}^{4+}$ ions, and the electron trap depth of ${V}_{\mathrm{O}}$ decreases by the combination with Ca; thus, the trapping/detrapping rates increase, leading to decay-time shortening. Hence, our study has demonstrated an effective way to gain insight into the mechanisms for tuning properties of optical materials by codoping. The principles of the obtained mechanisms provide guidance for designing and optimizing a broad range of functional materials.