Tez Özeti

In this thesis, we examined optical properties of the commercially available yellow and red phosphors in polymethylmethacrylate (PMMA) matrix together with light -harvesting nanoparticles; TiO₂ and TiO₂:Cr³⁺. The yellow and red phosphors of La₃Si₆N₁₁:Ce³⁺ (LSN) and (Sr,Ca)AlSiN₃:Eu²⁺ (SCASN) were chosen due to their superior properties including optical brightness, excitation ability by blue light, thermal resistivity, hardness and high chemical stability. Both the LSN and silicate-based nitride phosphor; SCASN are promising conversion materials for white-light emitting diode (WLEDs) applications and other optoelectronics. Excitation and emission behavior of the offered materials were investigated by the spectrofluorimetric measurements. The excited state lifetimes of the presented materials were recorded both in nanosecond and microsecond time scales, respectively. The blended forms of the LSN and SCASN with Cr³⁺ activated TiO₂ nanoparticles exhibited extraordinary performance in terms of optical emission. We attributed the observed enhancement to the energy transfer from Cr³⁺ activated TiO₂ NPs to the phosphors.

In the second part of the thesis, newly synthesized 2-(9-Hexyl-9H-carbazol-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazole (YEN 5) dye specified in the plasticized PMMA matrix, together with the silver nanoparticles (AgNPs). The offered dye exhibited a spectral sensitivity towards ionic mercury both in the absence and presence of the AgNPs. The composite was designed in form of thin film and electrospun nano fibers to test the sensitivity for the quantification of the Hg (II). The better spectral results observed for the silver containing blends were assigned to the energy transfer from AgNPs to the dye which is also explained with is theoretical background in this thesis. Similarly, the decay characteristics of the dye-based compositions were measured in nanosecond time-regime. The presented composites can bring a new approach for the LED technologies in terms of phosphor materials and dye-based optical mercury sensing applications.

Keywords: Phosphor, La₃Si₆N₁₁:Ce³⁺, (Sr,Ca)AlSiN₃:Eu²⁺, luminescence, mercury, titanium dioxide, silver nanoparticles.