半导体纳米颗粒/金属-有机骨架复合光催化体系中的位置效应

本文采用超快瞬态吸收光谱技术研究了“半导体/金属-有机骨架(MOF)”复合体系中的位置效应. 半导体TiO₂纳米颗粒被嵌入或担载于一种典型的MOF材料Cu₃(BTC)₂. 通过实时跟踪这两个复合体系中的电子动力学行为,发现半导体与MOF之间形成的界面态可作为高效的电子转移纽带,其效率与二组份的相对位置密切相关,从而导致这两个复合体系光催化CO₂还原的性能差异. 本文对“半导体/MOF”复合体系中界面电子转移行为和效应的机理进行了解读,为基于MOF材料的光电化学应用提供了有益的设计思路.     

二维MoS2/MoSe2异质材料的电子结构和热电性质研究

利用密度泛函理论结合玻尔兹曼输运理论计算体相和双层二维MoS₂/MoSe₂异质材料的热电性质. 计算表明,体相MoS₂/MoSe₂异质材料的热电性质比之于MoSe₂会有较大程度的提高. 该异质材料热电性质的提高主要源于异质材料本身带隙的减小以及层间的范德瓦尔斯相互作用. 二维MoS₂/MoSe₂异质材料存在热电应用的可能性.     

4-硝基联苯酚三重态质子化和去质子化过程中瞬态物种的指认

近年利用超快光谱技术对于4-硝基联苯酚(HO-Bp-NO₂)的研究发现，其在单重态和三重态时均会发生光致质子耦合电子转移(PCET)反应. 其瞬态吸收光谱450 nm处有一个独特的尖锐吸收带，但无羟基取代的对硝基联苯(Bp-NO₂)未观察到此现象. 本文利用酸性溶液作为外加可控质子供体，通过在强酸(∽10^-1 mol/L)和弱酸(∽10^-4 mol/L)溶液中的光谱和动力学结果，指认这个新吸收带为开壳层单重态O-Bp-NO₂H. 它是HO-Bp-NO₂的互变异构体，由三重态HO-Bp-NO₂中硝基氧得质子后羟基快速去质子产生. 动力学分析表明，非质子极性溶剂中三重态HO-Bp-NO₂与基态母体间还会发生PCET或先质子后电子转移生成自由基·O-Bp-NO₂. 这一反应与O-Bp-NO₂H竞争，导致其产率较低. 这些结果阐明了三重态HO-Bp-NO₂在非质子极性溶剂中的失活机制.     

二硫化钼纳米点中的缺陷辅助载流子俘获超快动力学

二硫化钼纳米点正在成为有潜质的半导体材料用于光电设备的应用.然而,关于对其中激子动力学的研究却很少.本文利用飞秒瞬态吸收光谱学来研究二硫化钼纳米点的载流子动力学.结果显示,缺陷辅助的载流子再复合过程与观测到的动力学相符,通过俄歇散射对光激载流子进行俘获至少存在两种不同俘获速率的缺陷.四个过程参与了载流子驰豫,在受到光激发后,立即在~0.5 ps内载流子冷却,然后大部分载流子被缺陷快速俘获,随着泵浦能量的增加,该过程对应的时间从~4.9 ps增加到~9.2 ps,这可以用缺陷态的饱和来解释.接下来,拥有相对慢的载流子俘获速率的其它类型缺陷对小部分载流子进行俘获,该过程约65 ps.最后,剩余的少量载流子通过直接带间跃迁发生电子-空穴再复合,时间约为1 ns.研究结果可以深入了解二硫化钼纳米点中的载流子动力学基本原理,引导其更多的应用.     

飞秒瞬态吸收光谱技术研究反式对氨基偶氮苯的超快激发态动力学 (cited: 1)

利用飞秒瞬态吸收光谱技术研究了反式对氨基偶氮苯(AAB)溶解在乙醇中的超快激发态动力学．当利用400 nm光激发分子到S₂态后,由S_{211102412相似文献}   

钙钛矿晶体的电荷复合动力学研究

本文利用紫外吸收光谱和稳态荧光光谱技术结合理论模型，研究了钙钛矿材料CH₃NH₃PbI₃晶体在光激发过程中的电荷复合动力学行为，进而获得晶体的扩散长度. 电荷载体的扩散长度是判断光电材料的重要参数. 研究通过合成两种不同缺陷态浓度的CH₃NH₃PbI₃晶体，测量这两种晶体在0.019∽4.268 μJ/cm²的激光激发下的时间分辨荧光光谱，利用动力学模型对光谱进行拟合，可以获得每个晶体的掺杂浓度，空穴浓度以及电荷复合参数. 将这些参数结合已有公式，最终可获得每个晶体的电荷载体的扩散长度.     

二硫化钼纳米点中的缺陷辅助载流子俘获超快动力学（英文）

二硫化钼纳米点正在成为有潜质的半导体材料用于光电设备的应用.然而,关于对其中激子动力学的研究却很少.本文利用飞秒瞬态吸收光谱学来研究二硫化钼纳米点的载流子动力学.结果显示,缺陷辅助的载流子再复合过程与观测到的动力学相符,通过俄歇散射对光激载流子进行俘获至少存在两种不同俘获速率的缺陷.四个过程参与了载流子驰豫,在受到光激发后,立即在～0.5 ps内载流子冷却,然后大部分载流子被缺陷快速俘获,随着泵浦能量的增加,该过程对应的时间从～4.9ps增加到～9.2ps,这可以用缺陷态的饱和来解释.接下来,拥有相对慢的载流子俘获速率的其它类型缺陷对小部分载流子进行俘获,该过程约65 ps.最后,剩余的少量载流子通过直接带间跃迁发生电子-空穴再复合,时间约为1 ns.研究结果可以深入了解二硫化钼纳米点中的载流子动力学基本原理,引导其更多的应用.     

吡啶离子液体与水混合体系中蒽醌-2-磺酸钠的激光闪光光解机理

利用激光闪光光解技术研究了蒽醌-2-磺酸钠(AQS)在吡啶离子液体N-丁基吡啶四氟硼酸盐([BPy][BF₄])与水(H₂O)混合体系中的光化学反应过程. 实验结果表明,AQS的激发三重态(³AQS^*) 会与H₂O快速反应,不断增加[BPy][BF₄]在混合体系中的体积比(V_IL),瞬态吸收光谱发生了很大变化. 510 nm附近的瞬态吸收带变化最大,在0< V_IL< 0.1时,吸光度会随着[BPy][BF₄]的增加而增加;而在V_IL>0.1时,吸光度则随着比例的增加而减小. 然而380 nm附近吸收带的吸光度却一直在增加. 通过拟合近似地得到了瞬态物种B和³AQS^*的表观动力学参数. 另外还讨论了³AQS^* 与阳离子之间的夺氢反应,通过对350~420 nm处光谱图的分析,推断出这一范围的瞬态吸收光谱是³AQS^*与AQSH^·的叠加谱. 在混合体系中,³AQS^*分别与H₂O和[BPy][BF₄]的反应是一对竞争反应. 还发现在高浓度的离子液体环境下,体系的整体反应速率会减弱.     

过渡金属Fe或Ag掺杂K2Ti6O13的电子结构和光学性质

本文利用基于密度泛函理论（DFT）的第一性原理计算研究了它们的电子结构和光学性质.光学性质的计算结果和实验相一致.结果表明,Fe或Ag掺杂后,K₂Ti₆O₁₃的带隙中出现了杂质带且其带隙值变小,因而使掺杂后的K₂Ti₆O₁₃的吸收边发生红移并实现了其对可见光吸收.其中杂质带主要由Fe 3d态或Ag 4d态与Ti 3d态和O 2p态杂化而成.对于Fe掺杂的K₂Ti₆O₁₃,杂质带位于带隙中间,因此可以作为电子从价带跃迁到导带的桥梁.对于Ag掺杂的K₂Ti₆O₁₃,杂质带位于价带顶附近为受主能级,可以降低光生载流子的复合概率.实验和计算研究表明,通过Fe或Ag的掺杂可以实现了K₂Ti₆O₁₃对可见光的吸收,这对进一步研究K₂Ti₆O₁₃的光学性质具有重要意义.     

MXene与溶剂界面电子振动耦合现象的直接观测

作为一种新型的二维材料,MXene凭借其各种优异的物理化学性质已受到极为广泛的关注,例如其具有极其出色的光热转换效率. 然而,人们对MXene的光热转换机制仍然知之甚少. 本文通过结合飞秒可见和中红外瞬态吸收光谱技术,对分散在各种溶剂中MXene(Ti₃C₂T_x)纳米片内的电子能量耗散动力学进行了系统的研究. 结果表明,MXene的激发态寿命在很大程度上取决于周围的溶剂环境. 在MXene被超快激光泵浦后,可以直接观察到MXene纳米片与相邻溶剂分子之间的界面电子振动耦合现象. 这些结果表明界面相互作用在MXene的超快能量传输动力学中起着关键的作用. 这一发现可为二维体系光转换性能的改进提供了一条潜在可行的途径.     

Multicolor Light‐Emitting Diodes with MoS2 Quantum Dots

Molybdenum disulfide (MoS₂) quantum dots (QDs) are known for their excitation‐wavelength‐dependent photoluminescent (PL) properties. However, the mechanism of this phenomenon is still unclear. Here, small size MoS₂ QDs with a narrow size distribution are synthesized. Based on the decay study and PL dynamics, a reasonable radiation model is presented to understand the special PL properties, i.e., the carrier recombination in the localized surface defect states generated the PL. Accordingly, this optical property is used to fabricate multicolor light‐emitting devices with the same MoS₂ QDs. The emission color covers the full visible spectrum from blue to red, only by adjusting the thickness of the down‐conversion QD layers.     

Deep level states and negative photoconductivity in n-ZnO/p-Si hetero-junction diodes

Negative photoconductivity (NPC) was observed in n-ZnO/p-Si heterojunction diode grown by ultra-high vacuum sputtering method under nitrogen ambient. Under the illumination of ultra-violet light, positive photoconductivity was observed at low bias voltages, whereas NPC was observed at high bias voltages. The defect states in the ZnO layers grown on Si were analyzed by photoluminescence and deep level transient spectroscopy measurements. Two deep levels were measured at E_c-0.51 eV and E_c-0.54 eV, which might be originated from oxygen vacancy and nitrogen atom related defects, respectively. Based on the simulation of band diagram, the defect states were located below Fermi level at zero bias voltage. However, as increasing the bias voltages, NPC was observed due to the increase of empty defect states. This analysis allowed us to consider the possibility that the NPC phenomenon in n-ZnO/p-Si heterojunction diode is originated dominantly from the defect states as a carrier recombination center in ZnO layer.     

Capture cross-section and density of deep gap states in a−SiHx schottky barrier structures

Recombination of charge carriers in a?SiH_x Schottky barriers with density of states near mid-gap ranging from 2.8×10¹⁵?7×10¹⁶cm^-1eV^-1 is attributed to recombination centers with hole capture cross-section of 1.3×10^-15cm².     

The effect of carrier gas flow rate on the growth of MoS<Subscript>2</Subscript> nanoflakes prepared by thermal chemical vapor deposition

Molybdenum disulfide nanoflakes (MoS₂) are superior material for their semiconducting properties. For bulk and monolayer MoS₂ the band gap changes from indirect-to-direct, respectively. So, it exhibits promising prospects in the applications of optoelectronics and valleytronics, such as solar cells, transistors, photodetectors, etc. In this research, the influence of different Ar flow rates as the carrier gas, is investigated for growing MoS₂ nanoflakes on silicon substrates using one-step thermal chemical vapor deposition by simultaneously evaporating of solid sources like sulfur and molybdenum trioxide powders. The structural and optical properties of the obtained nanoflakes are assessed by using X-ray diffraction pattern, scanning electron microscopy, UV–visible absorption, photoluminescence and Raman spectroscopy. It is shown that, Ar gas flow rate is strongly affects on the final products as few-layer MoS₂ structures. Moreover, the abundance of MoS₂ in comparison to MoO₂ and MoO₃ structures, in the obtained nanoflakes, is influenced by the Ar flow rate.     

Synthesis, structure and photocatalytic activity of nano TiO2 and nano Ti1-xMxO2-δ (M = Cu, Fe, Pt, Pd, V, W, Ce, Zr)

We have synthesized 5–7 nm size, highly crystalline TiO₂ which absorbs radiation in the visible region of solar spectrum. The material shows higher photocatalytic activity both in UV and visible region of the solar radiation compared to commercial Degussa P25 TiO₂. Transition metal ion substitution for Ti⁴⁺ creates mid-gap states which act as recombination centers for electron-hole induced by photons thus reducing photocatalytic activity. However, Pt, Pd and Cu ion substituted TiO₂ are excellent CO oxidation and NO reduction catalysts at temperatures less than 100° C.     

Photoconductivity of Se85−xTe15Hgx thin films

The photoconductive properties such as dark conductivity, steady state and transient characteristics of a-Se_85−xTe₁₅Hg_x thin films, prepared by thermal vacuum evaporation technique have been studied in the temperature range 312–380 K. Analysis of data shows that the activation energy of dark current is greater as compared to the activation energy of photocurrent. The activation energy increases at higher concentration of Hg which shows that the defect density of states decreases. Analysis of intensity dependent photoconductivity shows that the bimolecular recombination is predominant. The transient photoconductivity shows that the carrier lifetime decreases with the increase in Hg concentration and increases at higher concentration of Hg. This decrease is due to the transition trapping process. Further the photosensitivity and carrier lifetime increases at higher concentration of Hg which also confirms that the density of defect states decreases.     

Investigation of Cu2ZnSnS4 thin-film solar cells with carrier concentration gradient

To investigate the effect of carrier concentration gradient on Cu₂ZnSnS₄ (CZTS) thin-film solar cells, the properties of CZTS solar cells were studied by numerical method. The photovoltaic performances of carrier concentration gradient CZTS solar cells were calculated by the solutions of Poisson's equation, continuity equation, and current density equation using AFors-Het v2.4 program. The carrier concentration gradient was changed to analyze its effect. Compared with CZTS solar cells without carrier concentration gradient, the photovoltaic performances of CZTS solar cells can be enhanced by using carrier concentration gradient absorber. The carrier concentration gradient can extend the distribution region of built-in electric field, which is beneficial to the drift of photo-generated carriers. However, the carrier concentration gradient also affects the recombination and series resistances of solar cells. When the defect density of CZTS layer is high, the photo-generated carriers are affected significantly by recombination, resulting in slight effect of carrier concentration gradient. Therefore, the defect density should be reduced to enhance the effect of carrier concentration gradient on improving conversion efficiency of CZTS thin-film solar cells.     

Photoconductivity in trans (CH)x: A proof for the existence of solitons?

The optical absorption spectrum has been measured on trans (CH)_x upon simultaneous illumination of the sample with a second light source. No additional mid-gap absorption has been observed nor have the characteristic i.r. peaks been found which are known to show up at 0.11 and 0.17 eV upon doping. On the other hand photoconductivity has been detected, and, from its size, one would expect that the i.r. features should appear provided that the electron-hole pairs preferentially decay into soliton-antisoliton pairs, as predicted by theory. The negative results thus suggests that photo-generated carriers do not relax into solitonic states.     

Electroluminescence in CuGaSe2 single crystals

Electroluminescence has been observed in p-type CuGaSe₂ single crystals. At room temperature these crystals exhibit a resistivity of about 10^?2 Ω cm. The electrominescence has been obtained by minority carrier injection from an indium electrode. Two peaks have been identified in the emission spectrum whose energies are 1.53 and 1.59 eV, respectively. These peaks could be caused by the recombination of injected minority carriers in acceptor centers which are localized in the forbidden gap near the valence band.