The Optical Properties Of Rare-Earth Doped BI₃TiNbO₉ Ferroelectric Oxide

Layered-perovskite ferroelectric Bi₃TiNbO₉ have attracted much attention due totheir high Curie temperature, high mechanical quality, and high resistivity. Bi₃TiNbO₉ isan excellent host material for rare earth ions doping because it has large band gap, lowphonon energy, and excellent physical and chemical stability. However, several opticalproperty problems still need to be resolved, such as what is the effect of poling on the pho-tonluminescence of the rare earth doped ferroelectric material, how about the ffuorescencetemperature effect below the room temperature, how to enhance the photonluminescenceintensity of the thin film, and what is the effect of rare earth ions doing on the optical ab-sorption properties of the thin film, and so on. Therefore scientists devote much energy toinvestigating the optical property of the ferroelectric material. In this thesis, photonlumi-nescence properties, ffuorescence temperature effect, optical waveguide property, linearand nonlinear optical absorption properties of the rare-earth doped ferroelectric materialswere investigated.The effect of poling on the photonluminescence properties of the rare earth dopedferroelectric materials were investigated. The upconversion photonluminescence intensi-ty and the piezoelectric properties of Bi₃TiNbO₉: Er³⁺, Yb³⁺ and Bi₃TiNbO₉: Tm³⁺, Yb³⁺ferroelectric ceramics enhance with the poling electric field intensity. This is because theinner electric field can be enhanced by poling, then the transition probability and pho-tonluminescence intensity increase. The photonluminescence spectra of Ba(Ti_0.8Zr_0.2)O₃-(Ba_0.7Ca_0.3)TiO₃: Eu³⁺ ceramics were analyzed by the JO theory. With the increasing ofthe poling electric field intensity, the piezoelectric constant and the JO theory parameterff2 increase. This is because the spontaneous polarization turn to the poling direction,then the piezoelectric property enhances. At the same time, the local symmetry of thecrystalline field around Eu³⁺ ions reduces, and the ff2 value increases.And then, the ffuorescence temperature dependence of the thermally coupled levels2H11/2 and 4S3/2 ffuorescence intensity ratio of Bi₃TiNbO₉: Er³⁺, Yb³⁺ ceramics was in-vestigated. The maximum sensitivity of Bi₃TiNbO₉: Er³⁺, Yb³⁺ ceramics is 0.0032 K-1at the temperature range 123～693K. Bi₃TiNbO₉: Er³⁺, Yb³⁺ ceramics has good thermal,physical and chemical stability, great upconversion photonluminescence intensity and low cost fabrication. The results imply that Bi₃TiNbO₉: Er³⁺, Yb³⁺ ceramic is promising forapplication in wide temperature range sensors.In order to understanding the effect of the laser ffuence and the substrate temper-ature during the pulsed laser deposition on the upconversion photoluminescence of thethin films, the upconversion photoluminescence of Bi₃TiNbO₉: Er³⁺, Yb³⁺ thin film werestudied. The upconversion photoluminescence intensity of the thin films can be enhancedby improvement of crystalline state and increasing of the grain size. First, with the im-provement of the crystalline state, the crystalline field effects can be enhanced, and thephotoluminescence intensity can be enhanced. Second, surface area and the number ofquenching particle reduce with the increasing of grain size, and then the upconversionphotoluminescence of the thin films can be enhanced. Third, the enhancement of upcon-version photoluminescence emission in large particle size films may be brought about bythe reduction of internal reffections due to the substantial decrease of domain wall density.In order to know more optical properties of the thin films, the optical waveguideproperty, linear and nonlinear optical absorption properties of Bi₃TiNbO₉: La³⁺ thin filmwere investigated. The intrinsic refractive index and the thickness of Bi_2.85La_0.15TiNbO₉and Bi2.25La0.75TiNbO9 thin films were obtained by the prism-coupler method. The filmhomogeneity and the film-substrate interface were analyzed using an improved versionof the iWKB method. Our results show that the refractive index of Bi_2.85La_0.15TiNbO₉and Bi2.25La0.75TiNbO9 thin films remains fairly constant throughout the thickness anddecreases rapidly near the film/substrate interface. The result shows that the thin filmshave a good uniformity. It also indicates that the interface layer is negligibly thin so asto not have any effect on the deposition of the Bi₃TiNbO₉: La³⁺ film. The linear opticalproperties (include band gap, linear index, linear absorption coefficient, and so on.) ofBi₃TiNbO₉: La³⁺ thin films were studied by transmittance measurement. The nonlinearabsorption coefficient were measured by open aperture femtosecond laser Z-scan method.Our results show that La³⁺ ions in thin films substitute the A site in perovskite layers whenLa³⁺ content x≤0.75, and the nonlinear absorption coefficient increases with the La³⁺content of the thin films. When the La³⁺ content x = 1.05, the substitution content ofBi³⁺ in (Bi2O2)2+ layers is high enough to aggravate the orthorhombic distortion of theoctahedra, leading to remarkable changes of the nonlinear absorption coefficient of thethin film. The results show that the nonlinear absorption coefficient of the thin film canbe manipulated by the doping content of La³⁺ ions. In this thesis, the effect of poling on the piezoelectric and the photoluminescenceproperties of the rare earth doped ferroelectric materials were investigated, which exploita new approach to piezoelectric properties research. Optical properties of the rare earthdoped Bi₃TiNbO₉ were studied, which offers the reference to understanding the opticalproperties and application of Bi₃TiNbO₉ thin films.