X-ray excited emission spectra, photoluminescence excitation and emission spectra, optical reflectivity spectra, and pulsed X-ray and optical excited luminescence decay measurements were reported for cerium-doped La2Hf2O7 powders prepared by solid state synthesis. A broad luminescence associated with oxygen vacancies was observed in the region 350–750nm with a peak around 460 nm. The photoluminescence spectra and the number of oxygen vacancies vary for samples annealed in oxidizing or reducing atmospheres and with the temperature of the synthesis process. Increasing the cerium concentration reduces the oxygen-vacancy-related emission due to the presence of Ce4+. First principles calculations predict that Ce4+ can substitute in Hf sites; this was confirmed from the optical reflectivity spectrum of cerium-doped La2Hf2O7. Photoluminescence excitation and emission spectra characteristic of Ce4+ charge transfer transitions and possibly Ce3+ were also observed. Although trivalent cerium may be present, no emission observed from cerium-doped La2Hf2O7 can be attributed to Ce3+ in La sites.

Luminescence Study of Cerium-Doped La2Hf2O7: Effects due to Trivalent and Tetravalent Cerium and Oxygen Vacancies. Y.Eagleman, M.Weber, A.Chaudhry, S.Derenzo: Journal of Luminescence, 2012, 132[11], 2889–96