Investigation of optical properties and stabilities of some phosphor/ organic dye/ combinations in polymeric matrices

Phosphors are commercially important chemicals because they are used as raw materials in mobile phones, personal computers, LCD screens, light emitting diode (LED) and white light emitting diode (WLED) technologies. In this thesis, commercially available phosphors of Lu3Al5O12:Ce3+ (LuAG:Ce3+), (Y,Gd)3Al5O12:Ce3+ (YAG:Ce3+) and CaAlSiN3:Eu2+ (CASN:Eu2+) were investigated to enhance their spectral properties rather than the known approaches. The green, yellow and red phosphors were chosen to represent a large spectral range available in the screen technologies as well as LED applications. All phosphors were prepared in thin film form in a polymethyl methacrylate (PMMA) matrix. The light harvesting materials of nano-scale ZnO and CuO, have been used to improve the spectral properties of the LuAG:Ce3+ and YAG:Ce3+. In this process, fluorescence, phosphorescence, and excited state lifetimes were monitored and promising experimental results were obtained. Mechanisms indicating possible energy transfers between the species have been revealed. In the second part of the thesis, the energy transfer between phosphors and Tris (1,10-phenanthroline) ruthenium (II) hexafluorophosphate dye (Ru(phen)3PF6) has been investigated. The binary blends of the LuAG:Ce3+, YAG:Ce3+ and CASN:Eu2+ with the Ru(phen)3PF6 exhibited promising results in the presence of the ionic liquid (IL). Long-term photo stabilities of the composites supported with the IL were investigated during 8 months. No significant effect of the IL on photo-stability levels was detected.Keywords: LuAG:Ce3+, YAG:Ce3+, CASN:Eu2+, phosphor, Ruthenium complex, ionic liquid, LED, WLED, photoluminescence, fluorescence, phosphorescence</p

MANIPULATION OF SPECTRAL PROPERTIES OF POLYMER EMBEDDED PHOSPHORS AND DYES BY USING METALLIC NANOPARTICLES

Tez Özeti &nbsp; 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. &nbsp; 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. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </table