Optical Switching and Photoluminescence in Erbium Implanted Vanadium Dioxide Thin Films
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Optical Switching and Photoluminescence in Erbium Implanted Vanadium Dioxide Thin Films Herianto Lim1, Nikolas Stavrias1, Jeffrey C. McCallum1, Robert E. Marvel2 and Richard F. Haglund2 1 School of Physics, University of Melbourne, Parkville, Victoria, Australia. 2 Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, U.S.A. ABSTRACT Vanadium dioxide (VO2) is a promising material for an optical switch due to the ultrafast and reversible transition between its two phases with contrasting optical, as well as electronic, properties. Meanwhile, erbium (Er3+) has been a standard optical amplifier for the current fiberoptic communication system. Hence, a combination of the two could be expected to make an optical switch capable of simultaneous optical amplification. In the present work, the optical switching and photoluminescence of Er-implanted VO2 were successfully demonstrated. Postimplantation annealing at 800°C or above was seen crucial for the activation of the Er centers in the VO2 crystals. INTRODUCTION Vanadium dioxide (VO2) is a transition metal oxide that undergoes a reversible insulator– to–metal transition (IMT) close to room temperature at Tc ≈ 67°C [1]. The IMT is accompanied by a reversible structural phase transition (SPT) from a low-symmetry monoclinic structure (M1) into a high-symmetry rutile structure (R) [2]. The former has relatively high transmittance for thin films (> 60%) while the latter is reflective to infrared light [3]. Switching between the two structures can be triggered by thermal heating [4], electrical or optical pumping [5,6], or even by applying mechanical pressure [7]. When triggered optically, the transition can occur in the subpicosecond regime [8], making VO2 an attractive material as a switching device with optical as well as optoelectronic applications. Trivalent erbium (Er3+) is a lanthanide ion that is commonly used as an optical amplifier, due to its fluorescence at ~ 1.5µm [9]. This fluorescence wavelength lies within the wavelength window of minimal transport loss in silica-based optical fibers, and its lifetime is relatively long compared to those of other fluorescent materials. As such, Er3+ has become a standard amplifier for current fiber-optic communication systems [10]. Incorporating Er3+ into VO2 offers the possibility of making an optical switch capable of simultaneous optical amplification. The technology could be used as, for example, an optical transistor, an optical modulator, or a smart LED that changes its response under different optical and electrical conditions. In the present work, the optical switching and the Er3+ photoluminescence (PL) in Erimplanted VO2 thin film samples were investigated. As the ion implantation was observed to induce disorder in the crystals, post-thermal annealing was carried out. According to Raman scattering measurements, the crystal quality of the annealed samples was similar to the unprocessed crystals. Hence, subsequent experiments could be conducted with the certainty that the processed samples cons
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