Luminescence study of cerium-doped La2Hf2O7: Effects due to trivalent and tetravalent cerium and oxygen vacancies

Abstract X-ray excited emission spectra, photoluminescence excitation and emission spectra, optical reflectivity spectra, and pulsed X-ray and optical excited luminescence decay measurements are reported for cerium-doped La 2 Hf 2 O 7 powders prepared by solid state synthesis. A broad luminescence associated with oxygen vacancies is observed in the region 350–750 nm 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 Ce 4+ . First principles calculations predict that Ce 4+ can substitute in Hf sites; this is confirmed from the optical reflectivity spectrum of cerium-doped La 2 Hf 2 O 7 . Photoluminescence excitation and emission spectra characteristic of Ce 4+ charge transfer transitions and possibly Ce 3+ are also observed. Although trivalent cerium may be present, no emission observed from cerium-doped La 2 Hf 2 O 7 can be attributed to Ce 3+ in La sites.