Luminescent and Structural Analysis of Nanosized Strontium Aluminate and Zinc Sulfide Phosphors
Date Issued
2006
Date
2006
Author(s)
Chen, Shih-Yen
DOI
en-US
Abstract
In the first part of this thesis, synthesis of Eu2+, Dy3+ -activated strontium aluminate nanosized phosphors via a novel reverse microemulsion process is reported. This new synthesis technique not only reduced the synthesis temperature of SrAl2O4:Eu2+, Dy3+ phosphors to as low as 900oC, but also reduced the phosphor particle size to nanometer scale. In the microemulsion process, nanometered-micellees trapped the constituent cations, leading to a reduction of the interdiffusion length and an enhancement of the reactivity of the precursors. The photoluminescence intensity of prepared phosphors was found to substantially depend on their crystallinity and the results also indicated that the main peaks of nanosized SrAl2O4:Eu2+, Dy3+ phosphors in the excitation and emission spectrum shifted to shorter wavelengths. The decay time of prepared phosphors was greatly increased when synthesized at elevated temperature.
In the second part of this thesis, synthesis of highly luminescent ZnS: Mn2+ nano-particles via a microwave irradiation technique using zinc 2-ethylhexanoate as a novel zinc precursor is reported. This process was revealed as an efficient technique for producing in-situ capping of 2-ethylhexanoic acid on the ZnS: Mn2+ nano-particle surface, resulting in high luminescence intensity due to effective surface passivation. The chemical interaction of the carboxylic acid group with the ZnS: Mn2+ nano-particle was investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The obtained results indicated that 2-ethylhexanoic acid is chemisorbed as a carboxylate onto the surface of ZnS:
Mn2+ nano-particles and the two oxygen atoms in the carboxylate are coordinated symmetrically to the Zn atoms, leading to the formation of the covalent Zn-O bond. The anion bound onto the nano-particle surface prevents particle agglomeration due to electrostatic repulsion between two adjacent particles. Electron spin resonance (ESR) study showed a hyperfine sextet indicating well separated Mn2+ states without agglomeration. The prepared ZnS: Mn2+ nano-particles showed bright yellow-orange luminescence at about 585 nm, characteristic of 4T1 (excited)-> 6A1 (ground) transition of Mn2+ ion at Td symmetry in ZnS crystals.
In the last part of this thesis, the effect of microwave irradiation power on the physical properties of ZnS: Mn2+ nanophosphors is investigated. A series of ZnS: Mn2+ nanoparticles is synthesized changing the microwave power (from 150 W-500 W) to study its effect on the physical properties of the ZnS:Mn2+ nanoparticles, when all other synthesis conditions are kept fixed. From the obtained experimental results, it is observed that with changing power, there is also some effect in the particle size, leading to change the band gap of the prepared nano-phosphors. In the photoluminescence spectra, the blue shift phenomena is also revealed due to the quantum size effect and the sample synthesized with microwave power of 300 W showed highest luminescence intensity because of more manganese ions going inside the host lattice. From this experiment, the synthesis condition with microwave power at 300W is proven to be the optimum condition for synthesizing the nano ZnS: Mn2+ phosphors in this process.
Subjects
奈米
鋁酸鍶
硫化鋅
螢光材料
nano-phosphors
strontiu
aluminate
zinc sulfide
Type
thesis
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