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Photoluminescence of Sr2 – xLnxCeO4 + x/2 (Ln = Eu, Sm or Yb) prepared by a wet chemical methodElectronic supplementary information (ESI) available: thermoanalytical, XRD and TEM studies; photoluminescence of undoped Sr2CeO4. See http://www.rsc.org/suppdata/jm/b2/b207756f/

2002; Royal Society of Chemistry; Volume: 13; Issue: 2 Linguagem: Inglês

10.1039/b207756f

1364-5501

Abanti Nag, T.R.N. Kutty,

Crystal Structures and Properties

A wet chemical route is developed for the preparation of Sr2CeO4 denoted the carbonate-gel composite technique. This involves the coprecipitation of strontium as fine particles of carbonates within hydrated gels of ceria (CeO2·xH2O, 40 < x < 75) by the addition of ammonium carbonate. During calcination, CeO2·xH2O dehydroxylation is followed by the reaction with SrCO3 to form Sr2CeO4 with complete phase purity. Doping of other rare-earths is carried out at the co-precipitation stage. The photoluminescence (PL) observed for Sr2CeO4 originates from the Ce4+–O2− charge-transfer (CT) transition resulting from the interaction of Ce4+ ion with the neighboring oxide ions. The effect of next-nearest-neighbor (NNN) environment on the Ce4+–O2− CT emission is studied by doping with Eu3+, Sm3+ or Yb3+ which in turn, have unique charge-transfer associated energy levels in the excited states in oxides. Efficient energy transfer occurs from Ce4+–O2− CT state to trivalent lanthanide ions (Ln3+) if the latter has CT excited states, leading to sensitizer–activator relation, through non-resonance process involving exchange interaction. Yb3+-substituted Sr2CeO4 does not show any line emission because the energy of Yb3+–O2− CT level is higher than that of the Ce4+–O2− CT level. Sr2 − xEuxCeO4 + x/2 shows white emission at x ≤ 0.02 because of the dominant intensities of 5D2–7F0–3 transitions in blue–green region whereas the intensities of 5D0–7F0–3 transitions in orange–red regions dominate at concentrations x ≥ 0.03 and give red emission. The appearance of all the emissions from 5D2, 5D1 and 5D0 excited states to the 7F0–3 ground multiplets of Eu3+ is explained on the basis of the shift from the hypersensitive electric-dipole to magnetic-dipole related transitions with the variation in site symmetry with increasing concentration of Eu3+. White emission of Sr2 − xSmxCeO4 + x/2 at x ≤ 0.02 is due the co-existence of Ce4+–O2− CT emission and 4G(4)5/2–6HJ Sm3+transitions whereas only the Sm3+ red emission prevails for x ≥ 0.03. The above unique changes in PL emission features are explained in terms of the changes in NNN environments of Ce4+. Quenching of Ce4+–O2− CT emission by other Ln3+ is due to the ground state cross-over arising out of the NNN interactions.