$5d$ electron delocalization of ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Pr}}^{3+}$ in ${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ and ${\mathrm{Lu}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$

$5 d$ electron delocalization of ${Ce}^{3 +}$ and $\Pr^{3 +}$ in $Y_{2} Si O_{5}$ and ${Lu}_{2} Si O_{5}$

E. van der Kolk, P. Dorenbos, C. W. E. van Eijk, S. A. Basun, G. F. Imbusch, and W. M. Yen

Phys. Rev. B 71, 165120 – Published 29 April 2005

Abstract

The energies of the $5 d$ excited states of ${Ce}^{3 +}$ and $\Pr^{3 +}$ impurities relative to the conduction band of the insulators $Y_{2} Si O_{5}$ and ${Lu}_{2} Si O_{5}$ were investigated through a temperature and spectrally resolved photoconductivity study. The effective ionization barrier of $\Pr^{3 +}$ from the $5 d$ state to the conduction band is found to be $0.15 eV$ smaller than that of ${Ce}^{3 +}$ in both $Y_{2} Si O_{5}$ and ${Lu}_{2} Si O_{5}$ . The difference is explained by a model, represented by rate equations, that takes into account interconfigurational $4 f 5 d \to 4 f^{2}$ relaxation for $\Pr^{3 +}$ , a process that is absent for ${Ce}^{3 +}$ .