ELECTRONIC-RAMAN-SCATTERING STUDY OF THE LOW-LYING ENERGY-LEVELS OF TRIVALENT CERIUM-DOPED YTTRIA

Electronic-Raman (ER) transitions from the ground level of the F-2(5/2) manifold to other 4f levels of trivalent cerium (Ce3+) in yttria (Y2O3) have been studied as a function of excitation wavelength and temperature. ER transitions were observed for Ce3+ occupying both the C3i and C2 sites in Y2O3. Energy-level positions of the Kramer doublets of Ce3+ in the C3i site were determined from this measurement. The levels of the F-2(5/2) manifold were at 978 and 1503 cm-1, while three of the four levels of the F-2(7/2) manifold were at 2270, 2996, and 3402 cm-1 above the ground level. Previous literature values of three of the four energy levels of the F-1(7/2) manifold of the C-2 site were confirmed. A level of the F-2(5/2) manifold of Ce3+ in the C-2 site at 666 cm-1 was also identified. For resonant excitation involving a 5d intermediate state, two-orders-of-magnitude enhancement in the ER transition strength was observed. This resonant enhancement effect makes the electronic-Raman-scattering technique site selective, since for resonant excitation of the intermediate state of a particular site the ER lines of that site become more intense than those belonging to the other site. The differential scattering cross section for the transition from the ground state to the lowest F-2(7/2) level was measured to be 2.2 X 10(-30) cm2 sr-1 ion-1 for the C-2 site, and 8.8 X 10(-30) cm2 sr-1 ion-1 for the C3i site. These experimental values of cross sections are compared to the theoretical estimates.