Studies On Optical And Electric Properties Of Rare Earth-Doped Bismuth Titanate Ferroelectric Thin Films

In this thesis, europium (Eu) doped bismuth titanate (BEuT) ferroelectric thin films were prepared on ITO coated glass and quartz substrates by using chemical solution deposition (CSD) method, the effects of substrate type, annealing temperature and Eu3+concentrations on structure and properties of the BEuT thin films were studied. To further increase properties of BEuT thin films, composite thin films technology were used to explore properties of different types of ZnO/BEuT ferroelectric composite thin films, and improved their Photolumineseence (PL) performance, thus understand their mechanism at last. The structure of the paper is as follows.(1) Bi3.45Eu0.55Ti3O12thin films were prepared on indium-tin-oxide (ITO)-coated glass substrates annealed at different temperatures. XRD results showed that BEuT thin films exhibit a polycrystalline bismuth-layered perovskite structure, no other peaks from impurity phase or secondary phase were observed. By scanning electron microscopy, the grain sizes of BEuT thin films increased with increasing annealing temperature. BEuT thin films exhibit high optical transparency in the visible wavelength region. The absorption edges of BEuT thin films are at the wavelength of about 350nm. BEuT thin films which were prepared on indium-tin-oxide (ITO)-coated glass substrates enhanced the ferroelectric properties. PL spectra of the thin films included two strong peaks which originated from two transitions of 594 nm (5D0â†'7F1) and 617 nm(5D0â†'7F2) . The BEuT thin films were excited more effectively under 350nm, which could be due to the effective energy transfer from Bi+ to Eu3+. This could be proved by the overlap of Bi3+emission spectra and Eu3+ excitation spectra. Bi3.5Eu0.5Ti3012 thin films deposited on quartz substrates annealed at different temperatures. With increasing annealing temperature, BEuT thin films which were prepared on quartz substrates, also showed properties comparable to those of BEuT thin films onto (ITO)-coated glass substrates. However, BEuT/quartz showed a higher optical transmittance and a stronger PL intensity.(2) The effect of the concentration of Eu3+ ions on the PL properties and optical properties of Bi4-xEuxTi3O12 thin films was studied. The experimental results revealed that Eu3+ concentrations directly enhanced PL properties. The PL properties of BEuT thin films were influenced greatly by concentration quenching. It was observed that the PL intensity was obviously related to the doping amount of Eu3+ ions. The maximum PL intensity was obtained for the BEuT thin films with quenching concentration x of about 0.40 on both substrates. The high concentration quenching value of Bi4-xEuxTi3O12 materials in this study indicated that there was thought to be an unusual concentration quenching effect of photoluminescence. The europium (Eu) doped bismuth titanate (BEuT) ferroelectric thin films were the most promising candidate materials for multifunctional optoelectronic devices. The doping contents of Eu3+ ions had little influence to the transmittance of BEuT thin films.(3) ZnO/BEuT composite thin films with different types were prepared and their photoluminescence properties were studied. The composition types included constituting layered composite ZnO/BEuT thin films and incorporating BEuT with ZnO to form ZnO/BEuT nano composite films, as well as ZnO-BEuT solid solution. The results indicated that all of these methods could improve PL properties of BEuT thin films significantly. But the first one was a little weak compared to the other two, because the contact of ZnO and BEuT was not so completely for this method, and hence the energy transfer was not so high accordingly. Instead, ZnO nano powder with high specific surface area could easily transfer incident light to Eu3+ions, and hence emitted visible light finally.