| Nanomaterials exhibit many excellent characteristics different from the traditional bulk materials, such as special electrical properties, optical properties, magnetic properties due to quantum size effect, surface and interface effect, small size effect and macroscopic quantum tunneling effect, and thus have broad application prospects as optical materials, electronic materials, magnetic, catalytic materials, and so on. Among nanomaterials, alkali metal niobate XNb O3(X = Li, Na, K) is a kind of excellent multifunctional material, which not only has good ferroelectric, piezoelectric, photovoltaic, photocatalysis, non-linear optical properties,but also has a photorefractive effect, low toxicity and chemical stability, thus, it has a wide range of uses in high-tech fields. Furthermore, rare earth elements(Re) has a rich level structure and a special electron shell structure showed some excellent features. Therefore, this dissertation is committed to study the design and preparation of alkali metal niobate micro/nano-materials for spectral modulation. Detailed research contents and results are as follows:(1) XNb O3(X = Li, Na, K) micro/nano-crystals were prepared by liquid ion exchange techniques. First, the precursor KNb O3 nanoparticles were prepared by hydrothermal method,the chemical activity of precursor KNb O3 nanoparticles were explored in XOH(X = Li, Na, K)solution, it was found that the as-prepared precursor KNb O3 nanoparticles were a new phase of KNb O3 and with a higher reactivity in Na OH solution. Secondly, the effects of reaction conditions(surfactant, the reaction medium) on structures and morphologies for Na Nb O3 and Li Nb O3 micro/nano-crystals were explored. It was found that surfactant and the reaction medium were the most significant impact on the phase type, size and morphology of Na Nb O3micro/nano-crystals, and the growth mechanism of Na Nb O3 micro/nano-crystals was analyzed in detailed. Thirdly, the optical properties of Na Nb O3 micro/nano-crystals and luminescent properties of Na Nb O3:Eu3+ nanocrystals were studied, it was found that Na Nb O3micro/nano-crystals had a strong SHG response, and their SHG intensities were consistent with the volumes and sizes; furthermore, Na Nb O3:Eu3+ nanocrystals showed a strong red emission.(2) The optical SHG properties of single hexagonal Na Nb O3 micro/nano-crystals with different morphologies and sizes were investigated. It was found that each single hexagonal Na Nb O3 micro/nano-crystal(samples No.1-No.3) exhibited strong second-order nonlinear response, and which SHG intensities showed a quadratic dependence of the incident power.By calculating the average intensity and measuring polarization response of each singlehexagonal Na Nb O3 micro/nano-crystal(samples No.1-No.3), it had demonstrated that the same crystal structure displayed a similar optical SHG response. Furthermore, SHG was independent of the morphology and identical for similar crystals, which was expected for a volume effect with a second-order susceptibility tensor depending on the material properties.Furthermore, the orientation of each various Na Nb O3 micro/nano-crystal was also established.(3) A series of Na Nb O3:Ln3+(Ln = Eu, Dy, Sm, Er/Yb) luminescent nanomaterials were prepared by sol-gel method, their crystal phase and morphology were tested. It was found that the incorporation of a small amount of Ln3+ions had no significant effect on the crystal structure for Na Nb O3, and the morphology was ~ 45 nm cubic nanoparticle. The influences external pulsed magnetic field on the fluorescence properties of Na Nb O3:Ln3+(Ln = Eu, Dy,Sm, Er/Yb) nanocrystals were investigated, and the possible reasons and mechanism of magneto-optical interaction were explored. For Na Nb O3:Eu3+nanocrystals, which the integrated photoluminescence(PL) intensities of 5D0â†'7F2 and 5D0â†'7F4 transitions were reduced with the increment of magnetic field and both blue shift and red shift of peaks were found, but there was no significant effect on the Eu3+:5D0â†'7F1 and 5D0â†'7F3 transitions, the reasons might be attributed to the result of the Zeeman effect by high magnetic field which had changed the crystal site symmetry around Eu3+ ions and sensitivity to changes of symmetry for Eu3+:5D0â†'7FJ(J = 1-4) transitions in Na Nb O3 nanocrystals. For Na Nb O3:Dy3+/Sm3+ nanocrystals, which the integrated PL intensities of Dy3+:4S3/2â†'4I15/2,4F9/2â†'4I15/2 and Sm3+:4G5/2â†'6H5/2,4G5/2â†'6H7/2,4G5/2â†'6H9/2 all were reduced with the increment of magnetic field, emission bands broadened and emission peaks occured degeneracy, the magnetic field strength increased, the displacement increased, degeneracy increased, this phenomenon should be attributed to the strong overlap in transition energy involving the Zeeman levels under magnetic field, increased the non-radiative relaxation among the energy levels. For magnetic tuning of upconversion luminescence in Na Nb O3:Er3+,Yb3+nanocrystals, Yb3+ions acted as the sensitizer for Er3+ions, the integrated luminescent intensities of both Er3+:4S3/2â†'4I15/2 and 4F9/2â†'4I15/2 transitions first increased with the applied magnetic fields and then decreased with the applied magnetic fields increasing further, the “mixing” effect caused by pulsed magnetic field related with spin-orbit coupling were under consideration to responsible for this phenomenon.(4) Red afterglow luminescent material Na Nb O3:Pr3+ was synthesized by high temperature solid state method. The fluorescence properties and afterglow luminescent properties of Na Nb O3:Pr3+ material were investigated, and the effect of Pr3+ concentration on afterglow luminescence properties were also investigated. The result showed that theafterglow performance was from1D2â†'3H4 transition of Pr3+ion, and the optimum doping contents of Pr3+ion is 4%, finally, the afterglow mechanism was analyzed: electrons were the main charge carriers. |
PDF Full Text Request