The luminescence properties of nanocrystalline Y2O3:Er3+ prepared via wet chemical synthesis were investigated. A broadening of both the reflectance spectrum and 77 K luminescence spectrum (lambda(exc) = 488 nm) was observed in the nanocrystalline material compared to bulk Y2O3:Er3+. The spectral broadening was attributed to the presence of Er3+ ions on the surface of the particle, which experienced different crystal fields than the ions buried in the core of the particle. Upconversion was observed in both the bulk and nanocrystal material following excitation with 650-nm or 800-nm radiation. Following excitation with 800-nm radiation, an enhancement of the red (F-4(9/2) --> I-4(15/2)) upconverted emission was observed and occurred as a result of the (I-4(9/2),I-4(11/2)) --> (I-4(13/2), F-4(9/2)) ion-pair process that directly populated the F-4(9/2) state. The magnitude of the red enhancement in the nanocrystalline material prepared via wet chemical synthesis was less than that of the identically doped bulk sample and less still than Y2O3:Er3+ nanocrystals prepared via a combustion synthesis technique. An explanation is proposed to account for the drastic difference in the red upconverted luminescence intensity.
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