الفهرس 
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Abstract
Up-conversion (UC) is a non-linear optical process that is responsible for converting low energy photons (e.g. infrared light) into higher energy (e.g. visible light using photon absorption mechanism. Up-conversion process is being widely studied due to its enormous applications such as bioimaging, laser sources, energy harvesting, and optical sensors. Although UC is highly efficient in different applications, the luminescence and efficiency (quantum yield) have some important limitations that make them impractical for real world applications. The main limitation in this process is that UC efficiency is quite low compared to other optical conversion processes such as quasi-phase matching nonlinear optics. Consequently, additional means of increasing the UC luminescence and efficiency are necessary. Getting benefit of plasmonic effect metal nanoparticles, such as gold nanoparticles (Au NPs), is one of the most significant ways to manipulate the problem of low conversion efficiency. For a long time, it has been shown that noble-metal nanoparticles (MNP) have intriguing property to interact with emitters such as Er3+ and enhance their luminescence, absorption and other optical properties because of its ability to couple and confine oscillating electric dipoles. Plasmons lead light inside deep sub-wavelength volumes in electromagnetic (EM) modes. UC process is influenced in two ways when the emitter is close to MNP. Firstly, the local field intensity is enhanced due to the plasmon resonance, leading to enhanced absorption. Secondly, the decay rates related to the MNPs are affecting the transitions probabilities of the Er+3 ion. The influence of MNP on UC process alters highly with the positions and polarizations of oscillating dipoles whether parallel (PPOL) or perpendicular (SPOL) orientations. In this thesis, a complete study about the influence of using plasmonic metallic nanostructures is presented, resulting to support the UC process under 780 nm laser excitation. The selected material is erbium-doped ceria or Sodium Yttrium Fluoride nanoparticles because of their promising optical properties besides the relatively low-phonon energy of the host. Red shifted to the higher wavelength in the resonance peak is happened as a result of increasing the diameter of metal nanoparticle. At the used pump wavelength, the field enhancement, γE , is 101.1 according to a refractive index of the surrounding medium of value 1.5 and radius of 30 nm. Simulations depict that around 103 enhancement is appeared in the UC luminescence after employing gold nanoparticles to UC system. At the optimum position, a significant improvement is achieved. For more clarifying, at an average distance of 0.9 nm between Er ions, and Irradiance of 1000 W/m2 in Er-Ceria nanocomposite, the efficiency witnesses an enhancement from 0.42% to 4.81% for green emission and from 0.0047% to 0.081% for the red one that corresponds to 11.45-fold and 17.23-fold, respectively. In addition, the effect of other parameters such as multi-phonon relaxations, irradiance on UC efficiency, according to the added gold nanoparticles are investigated. Such promising modeling outcomes could help in further studies and applications.