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Composite ZnO-Yb2O3-Er2O3 transparent ceramics: structure and spectral-luminescent properties

We report on the structure and spectral-luminescent properties of a composite ZnO-Er2O3-Yb2O3 optical ceramic. The ZnO ceramic codoped with 1 wt% Er3+ and 4 wt% Yb3+ was prepared by uniaxial hot pressing of oxide powders at 1180 °C in vacuum. The maximum total transmittance of the ceramic is ~40%. The ceramic is a composite material comprised of hexagonal ZnO microcrystals (mean size: 10-15 μm, a = 3.251 Å and c = 5.201 Å) and cubic sesquioxide Er2O3 and Yb2O3 nanocrystals (mean size: ~130 nm, a = 10.450 Å and 10.555 Å, respectively). Its texture is dominated by the ZnO prism planes (100). The absorption spectrum of the ceramic demonstrates bands characteristic of Er3+ and Yb3+ ions in the Er2O3 and Yb2O3 crystals, respectively. The ceramic exhibits intense red upconversion luminescence. The X-ray induced luminescence spectrum contains two intense emission bands. The more intense one with a maximum at ~390 nm is due to the near-band-edge transitions and its decay time is ~1 ns. The broad band in the green represents defect emission. Its decay deviates from the single-exponential law revealing several characteristic times of ~6, 60 and 250 ns. The free carrier concentration of the composite ceramic is ~7.65×1018 cm-3, which is significantly higher than that for the undoped ZnO one.