Study of the Luminescence of Eu-Doped Nanocrystalline Si/SiO 2 Systems Prepared by RF Co-Sputtering
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G.A. NERY*, A. MAHFOUD**, L.F. FONSECA, H. LIU**, 0. RESTO, AND S.Z. WEISZ Physics Department, University of Puerto Rico, San Juan, PR, USA. *Physics and Chemistry Department, University of Puerto Rico, Arecibo, PR, USA. "**PhysicsDepartment, University of Puerto Rico, Mayaguez, PR, USA. ABSTRACT We prepared Eu-doped films of Si nanoparticles embedded in Si0 2 using pellets of Eu 20 3 by sputtering. We studied their photoemission, transmission and fluorescence to obtain data about their composition and particle size and the Eu interaction characteristics. We were able to incorporate Eu(III) into the Si nanoparticle / Si0 2 host. We also found we obtained Eu(II) in the process. We found a lowering of photoluminescence intensity with lowering of temperature. An as yet unanswered question is the reason for the intense whitish luminescence found in some regions of the samples. Some involvement with Eu(II) is suspected. Eu(IIl) related peaks were only observed where the size distribution peak of the nanoparticles was lower than 1.3nm. Whitish luminescence was related to peak sizes ranging from 1.Inm to 1.4nm. Annealing the samples had clear effects upon their photoluminescence, but did not necessarily involve changes in particle sizes, nor were these size changes necessary to increase luminescence. The Eu doping has a tendency to halt the annealing effects on size and, when changes did occur, the particles generally became smaller. INTRODUCTION Europium is an interesting material when incorporated as a dopant into solid state materials. This is because trivalent Eu(III) ions can be used as a structure probe, and due to its large quadrupole splitting and spin-lattice relaxation times, Eu(III) is particularly attractive in high-resolution laser spectroscopy [1]. One proposed application is in a frequency domain optical data memory, based on the large ratio of inhomogeneous-to-homogeneous line widths present. In some solid state materials the Eu(III) dopant ions exhibit the longest ever dephasing time of 822ýts and the narrowest homogeneous line width at low temperature [2]. This has stimulated interest in searching for appropriate materials to host Eu(III) ions, which could be optimized for operation at room temperature. We have produced and studied Si/Si0 2 material in which visible light emitting Si nanoparticles are embedded in a Si0 2 matrix. We made subsequent studies incorporating another rare-earth metal, Er, into the Si nanoparticle embedded Si02 matrix and verified that the luminescence of Er is enhanced due to energy transfer between the nanoparticles and the Er [3]. These considerations led us to attempt to ascertain the interactions between Eu and this new host material. Due to the amorphous nature of the Si0 2 material prepared by this particular technique, the dopant europium ions must experience large variations of their environment. Additionally, some Eu(III) ions may be placed at the Si nanoparticle / Si0 2 interface while the others are inside the Si0 2 host. This would produce fluorescence line broad
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