The Synthesis And Spectral Properties Of Gd₂O₃: Ce, Bi And YAG: Ce, Bi Nanophosphor

Nanosized rare-earth materials have been widely used in luminescence, optical fibers and amplifiers, fluorescence labeling etc. 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. So, more and more attention has been paid to improve currently used phosphors or explore novel efficient phosphors. 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:Er and YAG:Ce we make a comprehensive study on effect of Bi³⁺ doping to photoluminescent properties of nanocrystalline Gd₂O₃:Er and YAG:Ce. The main contents and the important results are listed as follows:1. Nanocrystalline Gd₂O₃:Er 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 and fluorescence spectrophotometry. The results showed that Gd₂O₃:Er with pure cubic phase was produced. The grain size was approximately 29.3 run. When excited at 376 nm and 980 nm, both photoluminescence and upconversion emission of Er³⁺ can be observed. The main emission peak of Gd₂O₃:Er was 559 nm, being attributed to (²H_11/2, ⁴S_3/2 )→⁴I_15/2 transitions of Er³⁺ ions. In addition, the influences of Er³⁺ concentrations on luminescent properties were studied and discussed.2. Gd₂O₃:Er,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 ( ²H_11/2, ⁴S_3/2 )→⁴I_15/2 transitions of Er³⁺ ions upon excitation with UV irradiation. The emission intensity of Er³⁺ ions was largely enhanced with introducing Bi³⁺ ions into Gd₂O₃:Er and the maximum occurred at a Bi³⁺ concentration of 1.5mol%. There was a highly efficient energy transfer from Bi³⁺ to Er³⁺ ions, leading to that the emission intensity of Er³⁺ at 559nm was largely enhanced. For higher concentration of Bi³⁺, the absorbed energy was non-radiatively dissipated due to the formation of Bi_n³⁺ aggregates, which results in an evident reduction of the sensitized effectiveness of Bi³⁺ ions on Er³⁺ ions.3. Nanocrystalline YAG:Ce 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, and fluorescence spectrophotometry. When excited at 455 nm photoluminescence emission of Ce³⁺ can be observed. The main emission peak of YAG:Ce was 530 nm, being attributed to5d→4f transitions of Ce³⁺ ions. In addition, the influences of Ce³⁺ concentrations on luminescent properties were studied and discussed.4. YAG:Ce,Bi powders were prepared at different doping concentrations. The emission spectra of all samples presented the characteristic emission peak arising from the5d→4f transitions of Ce³⁺ ions upon excitation with 455 nm. The emission intensity of Ce³⁺ ions was largely enhanced with introducing Bi³⁺ ions into YAG:Ce and the maximum occurred at a Bi³⁺ concentration of 6mol%. There was a highly efficient energy transfer from Bi³⁺ to Ce³⁺ ions, leading to that the emission intensity of Ce³⁺ at 530nm was largely enhanced. For higher concentration of Bi³⁺, the absorbed energy was non-radiatively dissipated due to the formation of Bi³⁺ aggregates, which results in an evident reduction of the sensitized effectiveness of Bi³⁺ ions on Ce³⁺ ions.