Photoluminescence from Silver Nanoparticles Enhanced by Surface Plasmon Resonance
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Photoluminescence from Silver Nanoparticles Enhanced by Surface Plasmon Resonance Oleg A. Yeshchenko1, Igor M. Dmitruk1, Alexandr A. Alexeenko2 , Mykhaylo Yu. Losytskyy1, Andriy V. Kotko3 and Anatoliy O. Pinchuk4 1
2
Physics Department, National Taras Shevchenko Kyiv University, 2/1 Akademik Glushkov prosp., 03127 Kyiv, Ukraine
Laboratory of Technical Ceramics and Silicates, Gomel State Technical University, 48 October prosp., 246746 Gomel, Belarus 3
4
I.M. Frantsevich Institute for Problems of Materials Science, 3 Krzhizhanovsky str., 03680 Kyiv, Ukraine
Department of Physics and Energy Sciences, University of Colorado at Colorado Springs, 1420 Austin Bluffs Pkwy, Colorado Springs, Colorado 80933, USA Abstract The size dependence of the photoluminescence spectra from silver nanoparticles embedded in a silica host medium was observed. The quantum yield of the photoluminescence increased when the size of the nanoparticles was decreased. The quantum yield for 8 nm silver nanoparticle was estimated to be on the order of 10-2 which is 108 times higher than the one observed for bulk silver. The two photoluminescence bands observed from silver nanoparticles were rationalized as the radiative electron interband transitions and radiative decay of the surface plasmons in silver nanoparticles. The strong local electric field induced by the surface plasmon resonance in silver nanoparticles enhances the exciting and emitted photons and increases the quantum yield of the photoluminescence.
1. Introduction Noble metal nanoparticles exhibit unique optical properties, such as resonant absorption and scattering of light, not found in bulk counterparts.1, 2 Collective coherent excitations of the free electrons in the conduction band are responsible for the strong absorption and scattering of the light by the particles.1 These coherent oscillations, also known as Surface Plasmon Resonance (SPR), lead to an enhanced local electric field close to the surface of the particles.1-4 The wavelength and width of the SPR band depend on the size, morphology, spatial orientation and optical constants of the particles and the embedding medium.2 The strong local electric field in the vicinity of the nanoparticles, sometimes referred to as the “hot spots”, can be used in surface enhanced spectroscopy, such as Surface Enhanced Raman Scattering (SERS)5, Surface Enhanced Infrared Absorption (SEIRA)6, Surface Enhanced Fluorescence,7 etc. While these methods received considerable experimental and theoretical attention,6, 8-10 the luminescence from noble metal nanoparticles has been studied very sparsely,11, 12 partly because of a very low probability of the corresponding radiative transitions.13-15 In contrast, the luminescence from bulk and nanostructured semiconductors (quantum dots, QD) has been extensively studied and well understood in terms of a radiative transition defined by the selection rules across the band gap between the conduction and valence bands. Since metals do not have a forbidden energy gap between occupied and un
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