Optical and Luminescent Properties of Highly Oriented Nanocrystalline Gd 2-x Eu x O 3 Thin Films
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1111-D04-11
Optical and luminescent properties of highly oriented nanocrystalline Gd2-xEuxO3 thin films S. Jáuregui-Rosas1,2, O. Perales Pérez3, S. P. Singh3, M.S. Tomar1, W. Jia1, and O. Vásquez1 1
Department of Physics, University of Puerto Rico at Mayagüez; Mayagüez-Puerto Rico 2 Departamento de Física, Universidad Nacional de Trujillo, Trujillo-Perú 3 Department of Engineering Science & Materials, University of Puerto Rico at Mayagüez; Mayagüez-Puerto Rico. ABSTRACT Highly crystalline and transparent Eu-doped Gd2O3 thin films were produced through a modified sol-gel method that did not require the use of any chelating agent. The effect of the atomic fraction of Eu3+ ions (‘x’ =0.05-0.30) on the structural, optical and luminescent properties has been studied. X-ray diffraction studies showed the preferential growth of Gd2-xEuxO3 thin films along the (400) plane corresponding to the cubic phase. UV-vis measurements revealed the high film transparency of the films in the visible region and a band gap value of 5.3eV. It has also been observed that the luminescence properties of the films were strongly dependent on both, the excitation wavelength and Eu concentration; the most efficient excitation conducive to red luminescence was achieved at the absorption band of Gd2O3 host (229nm). Under this condition all films exhibited strong red emission that is characteristic of Eu3+ ions. The emission intensity was also dependent on the doping level; the most intense luminescence was obtained at ‘x’=0.15. The drop in the luminescence intensity observed for ‘x’ values higher than 0.15 was attributed to quenching concentration effect. INTRODUCTION The high stability in vacuum systems and absence of corrosive gas emission under electron bombardment, which is a key issue in field emission devices, makes oxide-based phosphors more promising than conventional sulfide-based materials. It has been shown that rare-earth sesquioxides (RE2O3) can be used as efficient host matrices for trivalent rare earth ions in the fabrication of nanocrystalline phosphor materials. Gadolinium oxide, Gd2O3, is one of those sesquioxides with a cubic structure at room temperature and a band gap of 5.4eV [1, 2]. From an application viewpoint, the use Gd3+ species as contrast agent for magnetic resonance imaging (MRI) opens interesting possibilities of using nanocrystalline RE-doped Gd2O3 phosphors as multifunctional fluorescence MRI labels [3] or immunoassays agents [4]. Among trivalent RE ions Europium (Eu), is a red emitting species whose sharp luminescence peaks are associated to intra-4f shell transitions. Although the spectral positions of Eu species are independent of the embedding matrix, their intensities may vary. Furthermore, the individual levels of Eu (except 5D0→7F0) are splitted up due to crystal field effects. On this basis, it results not surprising the increasing attention that the preparation and functional characterization of Gd2O3:Eu3+ thin films are from the scientific community [2, 5, 6]. In this regard, the sol-gel route is a sim
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