Rare Earth Doped Spectral Conversion Materials And Biological Fluorescent Probe Application

The preparation, characterization and application of rare earth doped spectral conversion materials were discussed in this thesis. The research on spectral conversion materials consists of two parts:the first is upconverting materials discussed in Chapter2and Chapter3, the second is downconvertion materials discussed in Chapter4.The Chapter1is an introduction of the background knowledge about the content of this thesis, i.e., the basic principle of photoluminescence and luminescence properties of rare earth ions, and the basic principle of spectral conversion.The synthesis, characterization and biolabeling application of NaYF4:Yb3+,Tm3+(Er3+) upconverting luminescent materials are discussed in Chapter2and Chapter3. While the preparation, characterization and luminescent properties of NaYF4:Tb3+,Yb3+and YVO4:Bi3+(Tm3+),Yb3+downconvertion luminescence materials are studied in Chapter4. The main advisements are as follows:1. NaYF4:Yb3+,Tm3+(Er3+) core upconerting nanoparticles (UNCPs) with a size of17-19nm and NaYF4:Yb3+,Tm3+(Er3+)/NaYF4core/shell UNCPs with a size of22-25nm were synthesized by wet chemical method using oleic acid and octadecence. The Energy Dispersive X-Ray Spectroscopy (EDS) analysis confirms that the doping in the UNCPs is similar to the initial reaction mixture. The UNCPs are hydrophobic due to the surface coating with oleate ligands, which were confirmed through thermogravimentric analysis measurement (TGA). Under the excitation of980nm, the upconverting luminescence intensity for core/shell UNCPs is dozens of times higher than the core UNCPs. This is due to the presence of a shell which protects the dopants in the core, especially those near the surface, from quenching arising from solvents and surface ligands. The reduction in quenching improves the overall upconversion quantum yield of the UNCPs.2. The hydrophobic oleate-stabilized NaYF4:Yb3+,Tm3+(Er3+)/NaYF4core/shell UNCPs were transfered to hydrophilic by the cross-linked PMAO-BHMT coating. The cross-linking process of BHMT and PMAO on the surface of nanoparticles was further substantiated using Fourier transform infrared spectroscopy (FTIR). The absence of free amine groups and the presence of amide groups as observed in the FTIR spectra indicate that the cross-linking process was indeed successful. The results of1H NMR and TGA also substantiated the cross-linking process. At various pH values, in different physiological buffers (phosphate, tris and borate buffers), and in serum supplemented cell growth medium the cross-linked core/shell UNCPs exhibit excellent colloidal stability. The cross-linking strategy makes sure cross-linked polymer does not get detached from the surface of nanoparticles. At last, we demonstrate the uptake of cross-linked UCNPs by LNCaP cells to obtain the yellow green cell imaging, showing their utility as biolables.3. NaYF4:Tb3+,Yb3+phosphors were prepared by hydrothermal method. A variety of characterization methods show that we have successfully synthesized pure hexagonal NaYF4:Tb3+,Yb3+materials, and the size of particles are about1-6μm. The strong Raman peak of samples located298.9cm-1confirms the lower phonon energy in NaYF4materials. Under the excitation of355nm pulse laser, the visible emitting of Tb3+ion but no near infrared emitting was observed in the NaYF4matrix single doped Tb3+ion. While in the NaYF4matrix co-doped with Tb3+and Yb3+ions, both the visible emitting of Tb3+ion and the near infrared emitting were observed. This demonstrates that there exists the energy transfer from Tb3+ions to Yb3+ions, which may be a cooperative energy transfer process.4. A zirconia-type tetragonal structure of YVO4:Bi3+,Yb3+downconversion material was prepared by high-temperature solid-state method. Raman spectral analysis shows that the maximum phonon energy of YVO4material is892.1cm-1When the low concentration of Bi3+ion or Yb3+ion is doped in the YVO4matrix, the Raman peaks and FTIR peaks of YVO4material are not changed. In the room temperature, both visible and infrared excitation spectra are composed of two parts: the intense excitation peak between250and300nm due to O2--V5+charge transfer transition, and the weak excitation peak between300and375nm due to charge transfer transition from Bi3+to V5+. This demonstrates that there is energy transfer from the charge transfer state (CTS) to Yb3+ion. The concentration quenching efficiency of Yb3+ion was estimated through the decay lifetime of the near infrared emitting. It is found that when the concentration of Yb3+ion is higher, the concentration quenching efficiency is more serious. From the results of visible and NIR spectral evolution with temperature, the possible mechanism in the sample for the NIR emission is mainly phonon-assisted energy transfer at room temperature, and mainly cooperative energy transfer at low temperature.5. The tetragonal structure of YVO4:Tm3+,Yb3+downconversion material was also prepared by high-temperature solid-state method. XRD peaks, Raman peaks and FTIR peaks of the samples are all the same for the YVO4:Bi3+,Yb3+materials. This means that the doped ions of Tm3+,Bi3+or Yb3+substitute the Y3+ions in the YVO4, and the structure of YVO4is not changed by the substitution. Both visible and infrared excitation spectra exist a broad excitation peak from260to350nm which is attributed to the O2--V5+charge transfer transition, and a peak of473nm which is due to the transition of Tm3+:3H6→1G4. These demonstrate that there is energy transfer from Tm3+ion to Yb3+ion. When the Yb3+concentration is32%, the energy transfer efficiency from Tm3+to Yb3+was estimated to be60%, and the theoretical quantum efficiency is calculated to be160.9%. The energy transfer rate from Tm3+to Yb3+in the YVO4:Tm3+0.5%,Yb3+32%is1.94×104s-1which is much faster than that of the Tb3+-Yb3+system, indicating that energy transfer in the YVO4material is very efficient. The possible mechanism for NIR emission in YVO4:Tm3+,Yb3+phosphor is that:upon the UV varying from260to350nm light excitation, the VO43-is excited from the O2-(2p) ground state to the V5+(3d) excited state, the excited VO43-transfer its energy to the1G4of Tm3+via resonance energy transfer, then the excited Tm3+transfer its energy via cooperative energy transfer to two Yb3+ions, who emit near infrared photons.