Spectroscopic properties of Er 3+ in sol–gel derived ZrO 2 films

Abstract

Films of ( x/2)Er 2O 3–100ZrO 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 ZrO 2 phase on Er 3+ 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 ZrO 2 with the addition of Er 2O 3 (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 ( 2H 11/2+ 4S 3/2)→ 4I 15/2 transition and the red (670 nm) downconversion fluorescence due to the 4F 9/2→ 4I 15/2 transition were observed, and their intensities increased with increasing the heat-treatment temperature regardless of the type of the ZrO 2 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 °C; x=5, below 700 °C), but was observed in the cubic ( x=1, at 800 °C or above; x=5, at 700 °C or above) and monoclinic ( x=0.1, at 600 °C or above) phases under excitations at 647 and 780 nm. The reason is probably that the f–f transition probability concerning the 4I 13/2, from which the excited state absorption occurs, varied sensitively with the local structure of Er 3+ ions in the different phase of ZrO 2.