Dynamic control of photoluminescence for self-assembled nanosheet films intercalated with lanthanide ions by using a photoelectrochemical reaction
Dynamic control of photoluminescence for self-assembled nanosheet films intercalated with lanthanide ions by using a photoelectrochemical reaction
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DOI：
10.1002/anie.200704608
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Matsumoto, Yasumichi
中科院分区：
文献类型：
--
作者：
Ida, Shintaro;Ogata, Chikako;Matsumoto, Yasumichi
通过层状氧化物的剥离合成的半导体氧化物纳米片是厚度约为1 nm的二维晶体。[1-4]新的层状材料及其薄膜可以分别通过静电自组装沉积（ESD）[5]和逐层（LBL）[6-8]技术重新组装。由于纳米片在水溶液中具有负电荷，因此它们可以与各种阳离子物质一起用作起始材料。由纳米片和镧系元素（Ln）离子制备的层状材料作为新的功能材料是有前途的，因为Ln离子具有独特的性质，例如发光和磁性，这些性质可归因于4f电子轨道。例如，由钛酸盐纳米片和Eu 3+离子制备的Eu 3+离子插层钛酸盐层状氧化物具有独特的发光性质。[9-11]层状氧化物从Eu 3+离子发出红色发射，这是通过钛酸盐纳米片的带隙的激发通过能量转移而诱导的，[9，10]并且从Eu 3+离子发出的发射通过插入的水分子而促进。[10]此外，在室温下的激发光谱中观察到由嵌入的水分子引起的光谱烧孔。[11]TiOx、NbOx和TaOx的纳米片在具有高于带隙的能量的UV照射下的光电化学反应期间给出高光电流。[12]这一发现表明，在带隙的激发期间，在价带中的空穴和导带中的电子之间产生大的电荷分离。因此，层状氧化物材料插入Ln离子同时表现出光致发光和光电化学反应期间的带隙的激发用UV光照射。本文报道的研究表明了一种新的形式的动态控制的光致发光的Ln离子插入在自组装的纳米片薄膜的TiOx和NbOx。Ln离子的光致发光性质通过诸如pH值的变化和阴离子物种的添加等因素而改变。[13-17]然而，很难动态控制Ln 3+离子的光致发光特性。在本系统中，嵌入的Eu 3+和Tb 3+离子的发射强度可以容易地通过改变所施加的电势来控制。纳米片/Ln 3+（Ti 1.采用LBL技术制备了81 O 4纳米片/Eu 3+（TiO/Eu）和Nb 6 O 17纳米片/Tb 3+（NbO/Tb）薄膜，并将其固定在掺硼金刚石电极上。TiO/Eu和NbO/Tb薄膜的化学成分均为EuxTi 1. 81 O 4（x= 0.20-0.30）和TbyNb 6 O 17（y= 1.30-1.50）。这些接近理论中性组成（Eu 0. 25Ti 1。81 O 4和Tb 1。33Nb6O17）。Ln 3+离子夹在纳米片之间（参见支持信息中的图S-1）。图1显示了用于测量光致发光的系统的示意图。将具有三个电极的光电化学电池放置在荧光分光光度计的样品室中，其中纳米片/Ln 3+膜充当工作电极。使用0.1M K2 SO 4溶液（pH 6.5）作为电解质溶液。图2示出了TiO/Eu和NbO/Tb膜在UV光（波长：260 nm）照射下的发射强度作为电势（扫描速率：20 mVs·s-1）的函数。Eu ~（3+）离子的红光发射（614 nm，5D_0 - 7 F_2）出现在电位高于约100 V的区域。2 V，但在低于该电位的电位区消失。当在592 nm（5D 0..
Semiconductor oxide nanosheets synthesized by exfoliation of layered oxides are two-dimensional crystals with a thickness of about 1 nm.[1–4] New layered materials and their films can be reassembled by electrostatic self-assembly deposition (ESD)[5] and by layer-by-layer (LBL)[6–8] techniques, respectively. Since the nanosheets have a negative charge in aqueous solution they can be used with various cationic species as the starting materials. Layered materials prepared from nanosheets and lanthanide (Ln) ions are promising as new functional materials because Ln ions have unique properties, such as luminescence and magnetic properties, that are attributable to the 4f electron orbital. For example, the titanate layered oxide intercalated with Eu3+ ions prepared from titanate nanosheets and Eu3+ ions has unique luminescence properties.[9–11] The layered oxide gives a red emission from the Eu3+ ions which is induced by energy transfer through excitation of the bandgap of the titanate nanosheet,[9, 10] and the emission from the Eu3+ ions is promoted by intercalated water molecules.[10] Furthermore, spectral hole burning caused by the intercalated water molecules was observed in the excitation spectra at room temperature.[11] Nanosheets of TiOx, NbOx, and TaOx give a high photocurrent during the photoelectrochemical reaction under UV illumination with an energy higher than that of the bandgap.[12] This finding indicates that a large charge separation is produced between the holes in the valence band and the electrons in the conduction band during excitation of the bandgap. Consequently, layered oxide materials intercalated with Ln ions simultaneously exhibit both photoluminescence and a photoelectrochemical reaction during excitation of the bandgap on illumination with UV light. The study reported herein demonstrates a new form of dynamic control over the photoluminescence of Ln ions intercalated in self-assembled nanosheet films of TiOx and NbOx. The photoluminescence properties of Ln ions are changed by factors such as a change in the pHvalue and the addition of anionic species.[13–17] However, it is difficult to dynamically control the photoluminescence properties of Ln3+ ions. In the present system, the emission intensities of the intercalated Eu3+ and Tb3+ ions can be readily controlled by varying the applied potential. The nanosheet/Ln3+(Ti1. 81O4 nanosheet/Eu3+(TiO/Eu) and Nb6O17 nanosheet/Tb3+(NbO/Tb)) films were prepared and fixed on boron-doped diamond electrodes by the LBL technique. The chemical compositions of the TiO/Eu and NbO/Tb films were EuxTi1. 81O4 (x= 0.20–0.30) and TbyNb6O17 (y= 1.30–1.50), respectively. These are close to the theoretical neutral compositions (Eu0. 25Ti1. 81O4 and Tb1. 33Nb6O17). The Ln3+ ions were sandwiched between nanosheets (see Figure S-1 in the Supporting Information). Figure 1 shows a schematic illustration of the system used for the measurement of the photoluminescence. The photoelectrochemical cell with three electrodes, with the nanosheet/Ln3+ film acted as a working electrode, was placed in the sample chamber of a fluorescence spectrophotometer. A 0.1 m K2SO4 solution (pH 6.5) was used as the electrolyte solution. Figure 2 shows the emission intensities of the TiO/Eu and NbO/Tb films under illumination by UV light (wavelength: 260 nm) as a function of potential (sweep rate: 20 mVsÀ1). The red emission of the Eu3+ ions (614 nm, 5D0-7F2) appeared in the potential region above about À1. 2 V, but disappeared in the potential region below this potential. The same profile was obtained when the emission was monitored at 592 nm (5D0 …