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Study on the Photoluminescence Properties of Gd2O3:Sm and Bi3+/Na+ Doped Gd2O3:Sm Nanocrystals

Author: LiuGuangSheng
Tutor: ZhangWeiFeng
School: Henan University
Course: Condensed Matter Physics
Keywords: Gd2O3 Sm Bi3+ Na~+ energy transfer enhanced luminescence
CLC: TB383.1
Type: Master's thesis
Year: 2008
Downloads: 24
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Abstract


Nanosized rare-earth materials have been widely used in luminescence, optical fibers and amplifiers, fluorescence labeling etc. because the rare earth ions possess the advantages of high efficiency and brightness at low voltage and high current, higher stability, uniform granularity and narrow distribution. Nanoscale phosphors have unique advantages in improving the spatial resolution of display unites. In the last decade, significant interest in investigation of nanosized rare-earth phosphor materials had been emerged due to the possibilities for advanced applications, especially for the field emission display (FED), the plasma display panels (PDP), the cathode ray tubes (CRT) and various flat panel displays. However, the luminescent efficiency of phosphor is reduced with the decrease of the grain size due to a large contribution of the surface states to the nonradiative transition. It was found that some ions as coactivators, even in very small quantities, could play an important role in the enhancement of the luminescent efficiency of phosphors. In this thesis, on the basis of studying of luminescent properties of Gd2O3:Sm, we make a comprehensive study on effect of Bi3+/Na+ doping to photoluminescent properties of nanocrystalline Gd2O3:Sm. The main contents and the important results are listed as follows:1. Nanocrystalline Gd2O3:Sm was prepared by combustion synthesis using citric acid as the fuel and metal nitrates as oxidants. The structural, morphological and luminescent properties of samples were investigated by XRD, TEM and fluorescence spectrophotometry. The results showed that Gd2O3:Sm with pure cubic phase was produced. The grain size was approximately 28.2 nm. When excited at 275 nm and 980 nm, both photoluminescence and upconversion emission of Sm3+ can be observed. The main emission peak of Gd2O3:Sm was 603.5 nm, being attributed to 4G5/2→6H7/2 transition. In addition, the influences of Sm3+ concentrations, annealing temperature and C/M molar ratio on luminescent properties were studied and discussed.2. Gd2O3:Sm,Bi powders were prepared at different annealing temperatures and doping concentrations. The emission spectra of all samples presented the characteristic emission narrow lines arising from the 4G5/2→6HJ transitions (J=5/2,7/2, and 9/2) of Sm3+ ions upon excitation with UV irradiation. The emission intensity of Sm3+ ions was largely enhanced with introducing Bi3+ ions into Gd2O3:Sm and the maximum occurred at a Bi3+ concentration of 0.5mol%. There was a highly efficient energy transfer from Bi3+ to Sm3+ ions, leading to that the emission intensity of Sm3+ at 603 nm was largely enhanced. For higher concentration of Bi3+, the absorbed energy was non-radiatively dissipated due to the formation of Bin3+ aggregates, which results in an evident reduction of the sensitized effectiveness of Bi3+ ions on Sm3+ ions.3. Gd2O3:Sm,Na powders with different doping concentrations were prepared by solution combustion synthesis. The excitation and emission spectra were measured. The results indicated the emission intensity of Sm3+ ions was enhanced with introducing Na+ ions into Gd2O3:Sm. The enhanced luminescence by Na+ doping is mainly regarded as the results of the flux effect of Na+ and the creation of oxygen vacancy by Na+ ion doping. The flux effect of the Na+ gives a better crystallization and larger grain size, reducing the luminescence quenching due to the surface defects which act as non-radiative transition probabilities, thus bringing on the increase of the luminescent intensity. The oxygen vacancy is result from the occupation of Gd3+ site by Na+ ion, acting a sensitizer for the effective energy transfer, resulting in the improvement of luminescent intensity.

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