Erbium doped ZrO 2 nanocrystals ranging from 30 to 80 nm in size were prepared by a sol-gel process with the presence of cationic (CTAB) and nonionic (PLURONIC P-127) surfactants, and the up-conversion emission was characterized. A strong green emission was produced by the transition 2 H 11/2 + 4 S 3/2 f 4 I 15/2 and enhanced 1 order of magnitude with the presence of PLURONIC P-127 at a molar ratio Mrp ) 0.0082 annealed 5 h at 1000 °C. A molar ratio of Mrc ) 0.2 CTAB annealed 0 min at 1000 °C induced an increment of 300% of the signal emitted. In both cases the enhancement was partly attributed to the high content of monoclinic phase and crystallite size. However, the dominant parameter for the enhancement of the luminescence was the elimination of residual contaminants and defects produced for surface recombination.

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