Core-shell nanoparticles are one of the most important and attractive research topics due to their excelent properties compared to nanocomposite particles. LEDs or light emitting diodes are made of nanoparticles called phosphor, which are responsible for converting blue light into yellow light. These phosphors, which are composed of host materials called yttrium aluminum garnet (YAG) or Y 3 Al 5 O 12 , are modified by cerium ions as dopant with different atomic percentages to form the term YAG:Ce. In fact, YAG:Ce phosphor is a key component in white light emitting diodes (LEDs), with its main functionality being the generation of yellow light. Generated yellow light from phosphor will be combined with blue light, emitted from chip, resulting in the generation of white light. Generated light in LEDs will often be scattered by SiO 2 nanoparticles, distributed within the optical window, aiming for a more homogeneous light output. One of the most important issues in LEDs along with phosphors is the scattering to maintain the Lighting uniformity. Scattering in LEDs is mainly caused by silica nanoparticles. The presence of silica and phosphor nanoparticles in LEDs creats the idea of forming a core-shell structure of these particles, which is the subject of the present study. This thesis aims to investigate the synthesis, structure, and optical properties of SiO 2 @YAG:Ce core-shell optical nanoparticles for solid-state lighting applications. The main idea in this research is to combine these functionalities in one particle, with its core being SiO 2 and its shell being phosphor. In this study core-shell nanoparticles with different Ce 3+ concentration from 0.25 to 2 atomic percentages were synthesized by the sol-gel method. The synthesis of nanoparticles were performed at different pH and the time of calcination as the second parameter in the sol-gel process were investigated. The results show that the synthesis of these nanoparticles is strongly dependent on pH and the optimal amount is determined according to the conditions of experminetal and raw materials. This value is optimal on 3 and increase of this value can lead to impure phases. Synthesized nanoparticles were characterized by X-ray diffraction (XRD), small Angel X-ray Scattering (SAXS) analysis, high resolution transmission electron macroscopy (HRTEM), Fourier transform infrared (FTIR), and photoluminescence spectroscopy. Luminescence characteristics of SiO 2 @YAG:Ce core-shell particles were compared with that of YAG:Ce/SiO 2 mixture composite. Obtained results showed that core-shell nanoparticles have comparatively much better optical properties, compared to YAG:Ce/SiO 2 mixture composite and can therefore be used in LEDs.
