Spectral hole burning in sol-gel-derived Eu 3+ -doped film
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The sol-gel technique was applied to the preparation of Eu3+ ion–doped films, which showed persistent spectral hole burning. A gel film of ∼3500-nm thickness was prepared by dip-coating of the solution synthesized from Si(OC2H5)4, CH3Si(OC2H5)3, Eu(NO3)3 ⭈ 6H2O, and hydropropyl-cellulose. The spectral hole was burned in the 7 F0 → 5D0 transition band of the Eu3+ ions at 7 K, the depth of which was 24% of the total fluorescence intensity and decreased as the heat-treatment temperature of film increased. It was found that the hole was thermally filled and erased above ∼170 K; the temperature at which the hole was erased was lower for the film heated at high temperature.
I. INTRODUCTION
The persistent spectral hole burning (PSHB) phenomenon of rare-earth ions is one of the most significant optical properties of rare-earth ions because of their potential ability for a high-density frequency-domain optical data memory.1 For practical use, high-temperature PSHB is required, and in most of the rare-earth ions PSHB is limited at low temperature. Sm2+ and Eu3+ ions are special cases favorable to high-temperature PSHB. Room-temperature PSHB was first observed for the f–f transitions of Sm2+ ion–doped fluoride single crystals.2 Since then, many bulk materials such as crystals and glasses have been doped with Sm2+ ions.3–9 As a host material, glasses are more favorable than crystals, because of their wide inhomogeneous width, compositional variety, and easy mass production. In addition to the Sm2+ ions, high-temperature PSHB has recently been observed in the Eu3+ ion–doped glasses.10,11 We have successfully used a sol-gel method in preparation of the PSHB glasses doped with Sm2+ and Eu3+ ions exhibiting PSHB.12,13 Of the many potential fabrication methods of PSHB devices, film formation on the glass substrate is one promising technique. A sputtering method has been applied to prepare the Sm2+ ion–doped glass-films.14,15 In contrast, the sol-gel technique also proves an excellent method for the preparation of many types of optical coatings. In this paper, we demonstrated the preparation of thick films of silica glass doped with Eu3+ ions exhibiting PSHB. In the sol-gel method, the films are prepared by dip or spin coatings. Although the thickness of the films
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J. Mater. Res., Vol. 15, No. 5, May 2000 Downloaded: 02 Apr 2015
is controlled by changing the concentration, viscosity of the solution, and withdrawal or spin speed, the maximum thickness of the films without cracking is less than a few hundred nanometers. The holes are observed on the fluorescence spectra of the rare-earth ions, and their strong fluorescence intensities are required. One way to increase the fluorescence is the formation of thicker films. Here, we prepared the Eu3+-doped film with the thickness of ∼3500 nm by the hydrolysis of Si(OC2H5)4, CH3Si(OC2H5)3, and Eu(NO3)3 ⭈ 6H2O, and the PSHB properties were measured as a function of temperat
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