Revealing the oxidation number and local coordination of uranium in Nd2Zr2O7 pyrochlore: A photoluminescence study

Uranium doped Nd2Zr2O7 is synthesized at 800 °C (NUZO-800) using gel-combustion method and characterized using X-ray diffraction, scanning electron microscopy (SEM), X-ray photoelectron microscopy (XPS) and time-resolved photoluminescence (TRPL). As prepared sample was annealed further at 900, 1000, 1100 and 1200 °C leading to increase in the size of the particle and the effect of same has been investigated on the photophysical properties of NUZO. Based on excitation and emission spectroscopy it was inferred that uranium stabilizes as +6 oxidation state in the form of UO66−. XPS measurement also establishes +6 oxidation state of uranium in Nd2Zr2O7. Both emission intensity and photoluminescence (PL) decay time increases with increase in temperature till 1000 °C beyond which lifetime saturates whereas emission intensity decreases. The decay curve shows two different chemical environments for uranate ion in Nd2Zr2O7 pyrochlore matrix.