5d electron delocalization of Ce3+ and Pr3+ in Y2SiO5 and Lu2SiO5
The energies of the 5d excited states of Ce3+ and Pr3+ impurities relative to the conduction band of the insulators Y2SiO5 and Lu2SiO5 were investigated through a temperature and spectrally resolved photoconductivity study. The effective ionization barrier of Pr3+ from the 5d state to the conduction band is found to be 0.15 eV smaller than that of Ce3+ in both Y2SiO5 and Lu2SiO5. The difference is explained by a model, represented by rate equations, that takes into account interconfigurational 4f5d→4f2 relaxation for Pr3+, a process that is absent for Ce3+.
The effects of rare earth lanthanum on sintering process and structure of MoSi 2 have been investigated by x ray diffraction and SEM.The results show that La 2O 3 is the unigue form of La in the sintered MoSi 2 bars.The sintering process is activated by the addition of La,and the relative density of sintered MoSi 2 is the biggest when the content of La reaches 0.8wt.% ?