Films of (x/2)Er2O3-100ZrO(2) (X = 0, 0.1, 1 and 5) were prepared by the sol-gel and dip-coating methods, and the influences of the type of ZrO2 phase on Er3+ spectroscopic properties were investigated. X-ray diffraction patterns show the existence of metastable tetragonal phase at low temperatures, which are probably caused by both the excess surface energy due to the small crystallite-size effect (J. Phys. Chem. 4 (1965) 1238) and the stabilization of ZrO2 with the addition of Er2O3 (J. Phys. Chem. B 106 (2002) 1909; J. Ceram. Soc. Jpn. 107 (1999) 1111). Under excitation at 488 nm, the green (525 + 545 nm) downconversion fluorescence due to the (H-2(11/2) + S-4(3/2)) --> I-4(15/2) transition and the red (670 nm) downconversion fluorescence due to the F-4(9/2) --> I-4(15/2) transition were observed, and their intensities increased with increasing the heat-treatment temperature regardless of the type of the ZrO2 phase. On the other hand, the intensity of red upconversion fluorescence also increased monotonically with the heat-treatment temperature under excitation at 780 nm, while the green upconversion fluorescence was hardly observed in the tetragonal phase (for the film with x = 1, below 800 degreesC; x = 5, below 700 degreesC), but was observed in the cubic (x = 1, at 800 degreesC or above; x = 5, at 700 degreesC or above) and monoclinic (x = 0.1, at 600 degreesC or above) phases under excitations at 647 and 780 nm. The reason is probably that the f-f transition probability concerning the I-4(13/2), from which the excited state absorption occurs, varied sensitively with the local structure of Er3+ ions in the different phase of ZrO2. (C) 2003 Elsevier B.V. All rights reserved.