【作者】 贾昌文；

【导师】 谢二庆；

【作者基本信息】 兰州大学 ， 凝聚态物理， 2007， 博士

【摘要】 TiO₂基半导体薄膜和纳米结构的研究与开发对半导体发光材料、自旋电子学、光催化剂以及染料敏化太阳电池等领域具有重要意义。稀土掺杂TiO₂薄膜和纳米材料可以获得从可见到红外波段的有效发光；Co掺杂TiO₂纳米材料可以获得具有室温铁磁性的纳米稀磁半导体；N的掺杂可以使TiO₂的吸收边延伸至可见光区。本论文主要在TiO₂材料的制备工艺以及对其进行掺杂等方面开展了工作，对材料的结构、光学以及磁学特性进行了研究。主要内容包括以下几个方面：（1）用Sol-Gel法制备了TiO₂:Tb薄膜并且研究了薄膜的发光性能。PL研究表明在可见光区410，432，467，493，550，590和624nm有较强的发光峰，分别对应于Tb³⁺离子4f层内的⁵D₃→⁷F₅，⁵D₃→⁷F₄，⁵D₃→⁷F₃，⁵D₄→⁷F₆，⁵D₄→⁷F₅，⁵D₄→⁷F₄和⁵D₄→⁷F₃跃迁。其中最强的发光为550nm的绿光发射。研究了绿光强度与Tb³⁺离子浓度的关系，发现当Tb³⁺离子浓度达到9.5mol％时发光强度最大，当Tb³⁺离子浓度高于9.5mol％后发生浓度猝灭现象。当在TiO₂:Tb薄膜中掺入Ce³⁺离子后，Tb³⁺离子的发光强度明显增强，表明在材料中存在Ce³⁺对Tb³⁺的敏化作用。获得的薄膜在半导体发光材料领域有潜在的应用价值。（2）用Sol-Gel法制备了TiO₂:Eu薄膜并且研究了材料的结构和发光性能，获得的薄膜有很强的红光（620nm）和近红外发光（815nm）发射，前者归因于Eu³⁺离子4f层内⁵D₀→⁷F_j的跃迁发光，后者是由于TiO₂中Ti³⁺离子的缺陷态引起的发光。研究了退火温度对薄膜发光的影响，并且讨论了稀土离子在TiO₂中的发光机理，随着退火温度的升高，Eu³⁺离子的红光发射强度先增大后减小，退火温度为700℃时红光最强。对比纯TiO₂薄膜的发光谱后发现TiO₂:Eu薄膜中存在自陷态激子（STE）向Eu³⁺离子的能量转移，当退火温度高于700℃后815nm的近红外光出现并且随着退火温度的进一步升高发光强度显著增强，在此基础上提出了能量转移机制，即在高温退火后材料存在从TiO₂基质到Eu³⁺离子的能量传递，同时Eu³⁺离子向TiO₂基质中的Ti³⁺缺陷态能量背传递，这导致了Eu³⁺离子的发光减弱而Ti³⁺离子的缺陷态的发光增强。（3）用电纺丝（electrospinning）法制备了直径为75nm左右的TiO₂纳米纤维。并且对TiO₂纳米纤维成功地进行了稀土（Er）掺杂，研究了TiO₂：Er纳米纤维的表面形貌，晶体结构以及光致发光特性。获得的材料有很强的位于566.6nm的绿光发射，是由于Er³⁺离子4f层内⁴S_3/2→⁴I_15/2的跃迁所致。随着退火温度的升高Er³⁺离子绿光发射显著增强，在室温下能用肉眼观察到。制备的纳米纤维在荧光材料领域有潜在的应用价值。（4）用电纺丝法获得了具有室温铁磁性的稀磁半导体（TiO₂：Co）纳米纤维。获得的纳米纤维其直径约为70nm，Co的掺杂浓度约为5mol％。用XRD分析了不同温度下空气中退火后材料的结构，没有发现与Co有关的杂相，随着退火温度的升高样品从锐钛矿转变到金红石相。通过VSM测量表明样品呈现室温铁磁性。分析发现TiO₂：Co纳米纤维的发光谱与纯TiO₂纳米纤维的发光谱不同，不仅存在TiO₂自陷态激子（STEs）的复合发光，而且包含Co²⁺离子掺杂引起的氧空位的发光，说明TiO₂：Co纳米纤维的铁磁性与氧空位有关，经过分析后认为：F中心交换（FCE）作用可能是产生材料铁磁性的原因，Co²⁺离子通过以被氧空位陷落的电子为媒介进行铁磁性耦合，从而使材料呈铁磁性。（5）用电纺丝方法制得TiO₂纳米纤维，然后在NH₃气流中长时间退火将N掺入TiO₂纳米纤维中。对其表面形貌，结构以及紫外-可见吸收特性进行研究后发现N掺杂TiO₂纳米纤维的光学带隙（2.7eV）相对于纯TiO₂纳米纤维减小了约0.46eV，即N的掺杂使TiO₂纳米纤维的吸收边延伸到了可见光区。获得的材料在光催化以及染料敏化太阳电池等领域具有潜在的应用价值。更多还原

【Abstract】 The research and development of TiO₂ based semiconductor films and nanostructures have potential applications in the fields of luminescent semiconductor materials, spintronics, catalysts and dye-sensitized solar cells. Strong luminescence from visible to near-infrared range can be obtained by incorporation of different rare earth ions into TiO₂ systems; Co-doped TiO₂ nanomaterials is a promising nano diluted magnetic semiconductors （DMS） with room temperature ferromagnetism; The incorporation of N make the absorption band of TiO₂ nanofibres shift from ultraviolet to visible range. The thesis is mainly concentrated on the preparation of TiO₂ materials and the incorporation of some metal and nonmetal ions into them, and investigated their structure, optical, luminescence as well as magnetic properties. The main content and conclusions of the thesis are as follows:（1） TiO₂: Tb films ions are obtained by sol-gel method and their photoluminescence （PL） properties were also investigated. Strong PL peaking at 410, 432, 467, 493, 550, 590 and 624 nm were found from PL spectra, which are due to the intra-4f transitions of ⁵D₃→⁷F₅, ⁵D₃→⁷F₄, ⁵D₃→⁷F₃, ⁵D₄→⁷F₆, ⁵D₄→⁷F₅, ⁵D₄→⁷F₄ and ⁵D₄→⁷F₃ of Tb³⁺ ions. Among them, the strongest emission is green PL at 550 nm and it can be observe with necked eyes. PL intensity attaches maximum when Tb³⁺ ions concentration is about 9.5 mol% and concentration quenching occurs when more Tb³⁺ ions are incorporated. PL intensity increases remarkably when Ce³⁺ ions are introduced into TiO₂: Tb film, this result is mainly due to the activation of Tb³⁺ ions by Ce³⁺ ions. The obtained films have potential application in luminescent semiconductor materials.（2） We also fabricated TiO₂: Eu films by sol-gel method. The samples were annealed at various temperatures in oxygen atmosphere for 1 h. With the increase of annealing temperature, PL intensity of visible emissions peaking at 620 nm due to Eu³⁺ ions increases firstly but then decreases, and reaches maximum when annealing temperature is 700℃. Energy transfer from STE state to Eu³⁺ ions is considered to exist in TiO₂: Eu system compared with PL spectra of pure TiO₂. PL intensity of 815 nm emission due to defect states associated with Ti³⁺ ions of TiO₂ host appears when annealing temperature is higher than 700°C and increases rapidly with increasing of annealing temperatures. We conclude that the energy back transfer from Eu³⁺ ions to defect level associated with Ti³⁺ ions dominants the emissions at high annealing temperatures, and leads to the decrease of visible emissions and the increase of near-infrared emission.（3） TiO₂ nanofibers with the diameter of～75 nm were fabricated by electrospinning method. Er³⁺ ions were successfully incorporated into TiO₂ nanofibres and the effect of annealing temperature on the morphology, structure and PL properties of the nanofibres was investigated. The strong green PL of Er³⁺ ions peaking at 566.6 nm was detected and the PL intensities increase with the increase of annealing temperature. At higher annealing temperatures of 600 and 800°C, a near-infrared emission peaking at 815 nm appear, which is ascribed to the defect states associated with Ti³⁺ ions. TiO₂: Er nanofibers can be used as a good candidate for nanophosphors because of the strong green photoluminescence of Er³⁺ ions.（4） We prepared TiO₂: Co nanofibers with an average diameter of -70 nm by electrospinning. XRD measurements showed that the nanofibres present anatase to rutile phase at annealing temperature of 420 to 800°C. The obtained nanofibres present room temperature ferromagnetism and the ferromagnetic moments decrease with increasing of annealing temperature. TiO₂: Co nanofibers show a PL band peaking at 473 nm composed of two emission bands due to STEs and oxygen vacancies through multipeak Gaussian fitting, which is different from that of pure TiO₂ nanofibers. These indicate that the oxygen vacancies may play an important role for ferromagnetism in TiO₂: Co nanofibers. The ferromagnetism may come from the ferromagnetic coupling of CO²⁺ ions via F-center which is the result of partially substitute of Ti⁴⁺ ions by CO²⁺ ions. From these results, we introduced a way to investigate the structure and origin of ferromagnetism in DMSs by PL measurements.（5） We fabricated N-doped TiO₂ nanofibers by electrospinning with annealing TiO₂ nanofibers under NH₃ flow. Their morphology, crystal structure and UV-Vis absorption properties were investigated. It is found that the optical band-gap of TiO₂: N nanofibres present a blueshift for about 0.46eV compared with that of pure TiO₂ nanofibers. This indicate that the incorporation of N extend the absorption band from UV to visible region. The obtained materials have potential application in the field of photocatalysts.更多还原