金属表面、光学多层膜和谐振腔对量子点光学性质的调制特性研究

发布时间：2018-07-11 14:31

本文选题：量子点 + 金属表面　；参考：《东南大学》2016年博士论文

【摘要】：受益于量子限域效应,半导体量子点具有很高的荧光量子产率和较大的三阶非线性极化率,可广泛应用于发光二极管、全光开关和量子点激光器等领域。如果将它们与金属表面、光学多层膜和谐振腔等特定的器件相结合,这些器件能够通过增强量子点周围的光子态密度或局域场强度来增强量子点的荧光量子产率和非线性光学响应,从而进一步提高量子点的光学性能。本论文着重研究这些器件对胶体半导体量子点光学性质的调制及其应用。我们制备了一个系列的具有不同SiO_2壳厚的Ag/SiO_2/CdS-ZnS核/壳/壳等离子体耦合器,通过调节CdS-ZnS核-壳量子点与Ag纳米粒子之间的距离来调制富含表面态的CdS-ZnS量子点的荧光发射。当SiO_2壳厚为10nm时,我们同时实现了带边发射(4倍)和表面态发射(17倍)的最大增强并且将表面态发射与带边发射的强度比增加至55%,实现了单一尺寸量子点的明亮的白光发射。实验结果分析表明荧光增强主要来源于对非辐射弛豫速率(k_(nr))的抑制。我们利用内置CdSe-ZnS核-壳量子点的SiO_2(SiO_2:QDs)层和TiO_2层作为交替层,制备了5个周期的全介质光学多层膜。由于光学多层膜的局域场增强特性,光学多层膜中SiO_2:QDs层的非线性折射率(n~2)是单层SiO_2:QDs薄膜的近3倍。由于光致折射率变化引起的禁带边移动,光学多层膜的透过率变化是单层SiO_2:QDs薄膜的～17倍。在30 GW/cm~2的飞秒激光的激发下,光学多层膜的透过率可下降80%。飞秒泵浦探测实验表明光学多层膜光开关的响应时间为～400 fs。我们制备了壳厚为15个CdS单层的"巨型" CdSe-CdS核-壳量子点,并致力于通过飞秒激光退火消除界面势垒,进而使放大自发辐射从类似体材料的CdS壳转移到量子限域的CdSe核。除643 nm的放大自发辐射峰外,我们还观察到了两个短波长的放大自发辐射峰,它们对应于涉及CdSe核的第二个(1P)和第三个(1D)电子量子化的壳的光学跃迁,这表明俄歇复合被非常有效地抑制。此外,我们还制备了一个系列的壳厚可控的纯纤锌矿相CdSe-CdS核-壳量子点。受益于体积的增加、电子-空穴空间部分分离和几乎没有缺陷的合金界面,随着壳厚的增加,这个系列的量子点的俄歇速率减小了 3个数量级以上。因此,壳厚为11个CdS单层的量子点的放大自发辐射阈值低至16 μJ/cm~2。超快瞬态吸收光谱表明纯相量子点的光增益具有创纪录的长寿命(1000ps)和巨大的带宽(170nm)。最后,我们将具有低阈值增益特性的纯相量子点自组装成咖啡环微腔,从而得到超低阈值(～2μJ/cm~2)的单模激光发射。
[Abstract]:Due to the quantum limiting effect, semiconductor quantum dots have high fluorescence quantum yield and high third-order nonlinear polarizability, which can be widely used in light emitting diodes, all-optical switches and quantum dot lasers. If they are combined with specific devices such as metal surfaces, optical multilayers and resonators, These devices can enhance the fluorescence quantum yield and nonlinear optical response of quantum dots by increasing the density of photon states around the quantum dots or the local field intensity, thus further improving the optical properties of quantum dots. This thesis focuses on the modulation of optical properties of colloidal semiconductor quantum dots by these devices and their applications. We have prepared a series of Ag- / SiO-2 / CdS-ZnS core-shell plasma couplers with different Sio _ 2 shell thickness. We modulate the fluorescence emission of CdS-ZnS quantum dots rich in surface state by adjusting the distance between CdS-ZnS core-shell quantum dots and Ag nanoparticles. When the shell thickness of SiO2 is 10nm, we realize the maximum enhancement of the band edge emission (4 times) and the surface state emission (17 times) at the same time, and increase the intensity ratio of the surface state emission to the band edge emission to 55. The bright white light emission of the single size quantum dot is realized. The experimental results show that the fluorescence enhancement is mainly due to the inhibition of the non-radiative relaxation rate (k _ (nr). Five periods of all-dielectric optical multilayers have been prepared by using the SiOs2: QDs layer and TiOs layer of CdSe-ZnS core-shell quantum dots as alternate layers. Because of the local field enhancement characteristics of the optical multilayer film, the nonlinear refractive index (nb2) of the SiO2: QDs layer in the optical multilayer film is nearly three times that of the SiO2: QDs thin film. Due to the shift of bandgap due to the change of refractive index, the transmittance of the multilayer is 17 times higher than that of the SiO- 2: QDs thin film. Under the excitation of a femtosecond laser of 30 GW / cm ~ (2), the transmittance of the optical multilayer can be reduced by 80%. The experimental results of femtosecond pumping show that the response time of the optical multilayer optical switch is 400 fs. We have prepared the "giant" CdSe-CdS core-shell quantum dots with a shell thickness of 15 CDs monolayers, and we are committed to eliminate the interface barriers by femtosecond laser annealing, thus transferring the amplified spontaneous emission from CDs shells of similar materials to the CdSe nuclei in the quantum limited domain. In addition to the amplified spontaneous emission peak at 643 nm, we also observed two short wavelength amplified spontaneous emission peaks corresponding to the optical transitions of the second (1P) and third (1D) electron quantized shells involving the CdSe nucleus. This suggests that the Auger complex is very effectively suppressed. In addition, we have prepared a series of pure wurtzite phase CdSe-CdS core-shell quantum dots with controllable shell thickness. The Auger rate of the quantum dots decreases by more than three orders of magnitude with the increase of shell thickness and the partial separation of the electron-hole space and the alloy interface with almost no defects. Therefore, the amplified spontaneous emission threshold of 11 CDs monolayer quantum dots is as low as 16 渭 J / cm ~ (-1). The ultrafast transient absorption spectra show that the optical gain of pure phase quantum dots has a record long lifetime (1000ps) and huge bandwidth (170nm). Finally, a pure phase quantum dot with low threshold gain is self-assembled into a caf 茅 ring microcavity, and an ultra-low threshold (2 渭 J / cm ~ (2) single mode laser emission is obtained.
【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O471.1

【相似文献】