Effect of Ce4+→Ce3+ conversion on the structural and luminescence properties of Ce4+ doped Gd2Ti2O7 pyrochlore oxide

Abstract

Ternary oxides with cerium oxide as dopant are now useful as blue chip for the production of WLED's. In this present work, pyrochlore oxides Gd2Ti2-xCexO7 with doping concentration x = 0, 0.04, 0.08, 0.12, and 0.16, were prepared through standard solid-state reaction route. A pyrochlore structured phase is formed in the synthesized series as confirmed by conventional techniques; i.e., X-ray diffraction and Raman spectroscopy. Both techniques were revealed a systematic unit cell expansion as a function of doping concentration. The SEM micrograph confirms the formation of spherically agglomerated micron sized grains. In the later section of the manuscript, Ce4+→Ce3+ conversion effect on structural and luminescent properties were investigated. A relatively larger amount of cell expansion and accumulation of the strain is observed in the pyrochlore structured reduced samples. X-ray photoelectron spectroscopic (XPS) was used to investigate the oxidation state of the Gd, and Ti cations and oxygen anion. PL excitation spectra showed two broad bands centered around 255 nm and 360 nm due to the 4f→5d transition of Ce3+ ions at λem = 425 nm. Moreover, PL emission spectrum shows a broad peak around 425 nm at λex = 360 nm due to the 5d to 2F7/2 and 2F5/2 transitions. We observed that for the Ce4+→Ce3+ conversion both the PL emission and excitation spectra give far better results as compared to unreduced samples. Concentration quenching effect was observed for the doping concentration of 4% of cerium dopant. For 4% doping of cerium ion, CIE chromaticity results showed that the reduced as well as unreduced samples produce a bright blue colored emission line. The present study provides an insight about the potential use of Ce4+→Ce3+: Gd2Ti2O7 to synthesize blue LED chips for the fabrication of WLED's.