Date

2017

Author

Abacı, Özde Ceren

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In recent years, light emitting materials especially trivalent rare earth ions (RE3+) doped inorganic borate phosphors have attracted much attention due to their useful applications in several fields, which include flat panel displays, white light emitting diodes (WLEDs), solar cells, thermoluminescence dosimeters. In this research, single phase Dy3+; Eu3+ doped Dy3+/ Bi3+; Dy3+/ Ce3+; Dy3+/ Eu3+; Tb3+/ Ce3+ codoped lanthanum orthoborate phosphors were prepared by microwave assisted solid state synthesis method using metal oxides and carbonates as initial reactants. This method is preferential for us because previous microwave treatment of mixture before heating sample at high temperature in furnace reduces duration of heat and leads to produce fine powders. Crystal structure, morphology, vibrational band modes, low frequency vibrational modes, photoluminescence properties of all synthesized phosphors were investigated by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Attenuated vi Total Reflectance (ATR), Far Infrared (Far-IR), Fluorescence spectrometers, respectively. The colors of phosphors were detected with CIE 1931 color space chromaticity coordinates and photographs of materials were taken under 355 nm excitation. The XRD patterns prove that undoped, single doped and codoped LaBO3 powder crystalline samples were prepared successfully. Except high doping concentrations of Ce3+ ions that lead to observation of XRD pattern of CeBO3 with very low intensities, no significant changes are observed in the patterns of doped LaBO3 products. SEM images of synthesized materials show that fine particle size and regular morphology were obtained. ATR spectra of the products support the formation of planar borate units (BO33-). Far-IR spectra showed the variation in low frequency vibrational modes LaBO3 with various type and amounts of doping. Results of the luminescence studies showed that optical properties of samples can be tuned by codoping. Especially, Dy3+/ Ce3+ and Tb3+/ Ce3+ codoped samples had highest luminescence intensity among the all synthesized phospors. Moreover, Luminescence lifetimes were recorded at the highest emission bands in order to explain possible energy transfer mechanisms. Emission colors of phosphors were presented as red, pale yellow, white, green and yellow-orange, for Eu3+ doped; Dy3+ doped and Dy3+/ Bi3+ codoped; Dy3+/ Ce3+; Tb3+/ Ce3+; Dy3+/ Eu3+ codoped phosphors respectively.  

Subject Keywords

Cerium., Terbium., Europium., Lanthanum., Luminescence., Solid state chemistry.

URI

http://etd.lib.metu.edu.tr/upload/12621201/index.pdf
https://hdl.handle.net/11511/26826

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Graduate School of Natural and Applied Sciences, Thesis