High Pressure Studies of Sm 2+ -Doped Sol-Gel Glasses
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HIGH PRESSURE STUDIES OF Sm2+-DOPED SOL-GEL GLASSES Vilma C. Costa, Yongrong Shen, and Kevin L. Bray Department of Chemistry, Washington State University, Pullman, WA 99164 Ana M. M. Santos Center of Nuclear Technology Development / CDTN, CP 941, Pampulha, Belo Horizonte, MG, Brazil, 30123-970 ABSTRACT Glasses containing nominally 1, 2, 5, and 10 wt% Sm2O3 in Na2O-Al2O3-SiO2 and Al2O3SiO2 were prepared from metal alkoxide solution using the sol-gel process. After low temperature heat treatment in air, the glasses were heated up to 800 oC under a flowing H2 atmosphere to reduce Sm3+ into Sm2+. Samarium ions in the divalent and trivalent states were identified by fluorescence measurements. The fluorescence properties of Sm2+ ions are discussed in relation to concentration of Sm2O3 and the glass matrix composition. Preliminary results of pressure studies on the luminescence spectra and lifetime of Sm2+ in the glasses are presented as well.
INTRODUCTION Samarium (II) doped crystals and glasses have attracted much attention for potential applications in lasers, fiber amplifiers and memory devices. Interest in materials containing Sm2+ has increased in recent years because of their hole burning properties and applications as optical data-storage materials. Macfarlane et al. [1] first observed persistent spectral hole burning spectra in Sm2+ in halide crystals at 2 K. Recently, persistent spectral hole burning has been observed at room temperature in fluoride crystals [2], borate glasses [3], and fluorohafnate glasses [4]. A new approach for the preparation of Sm2+-doped aluminosilicate glasses using the sol-gel process has been reported [5] and room temperature persistent spectral hole burning has been observed in these systems. Glass systems are expected to be more desirable for high density memory devices than crystals because of their large inhomogeneous line widths and convenient sample preparation. The sol-gel technique is an especially attractive glass preparation method since lower processing temperatures are required relative to conventional melting techniques and the high porosity of sol-gel glass promotes reduction of Sm3+ to Sm2+ in presence of H2. Sm2+ has a ground 4f6 configuration and an excited 4f55d configuration. The close proximity in energy of the two configuration leads to a mixing of the states from the two configurations and to an alteration of the optical properties of Sm2+. With high pressure we can tune the extent of mixing of the two configurations by varying their energy separation. As a result, we can systematically investigate how the extent of mixing varies the static and dynamic emission properties of Sm2+ and correlate the emission properties with crystal field strength and coordination environment. There has been considerable progress in understanding the spectral properties of rare earth ions under pressure. The effects of pressure on spectral properties of Pr3+ [6], Nd3+ [7], Sm2+ [8] and Eu3+ [9] in crystals and Eu3+ [10] and Sm3+ [11] in glasses have been reported.
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