共查询到20条相似文献,搜索用时 24 毫秒
1.
使用化学胶体法合成了CdSe量子点,研究了样品的荧光量子产率,发现随CdSe量子点粒径的增大,荧光量子产率存在先增大后减小的现象.研究了CdSe量子点的色度学特性,通过对不同尺寸、不同粒径分布范围的CdSe量子点色度坐标的计算,讨论了粒径分布范围对其荧光颜色饱和度的影响,解释了为何难以获得高颜色饱和度的绿光量子点.利用红、蓝两种不同尺寸的量子点配制出白光样品,提出了估计配色后样品色度坐标的经验公式,结果显示白光样品色度坐标的实验值与经验公式估计值基本一致. 相似文献
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文章主要研究了CdSe量子点微腔结构,微腔结构包括上下分布式布拉格反射镜(DBR),中间的有源层为溶解在聚甲基丙烯酸甲酯(PMMA)中的CdSe胶体量子点.采用传递矩阵法模拟微腔的反射光谱,对实验测试曲线进行较好的拟合.通过测试微腔结构的光致荧光(PL)光谱,其半峰宽(FWHM)由未加入微腔的CdSe量子点样品的27.9 nm,减小到微腔结构的7.5 nm,在微腔中的量子点,由于腔模式的出现,其发光谱的品质因数增加了3.6倍,达到了荧光增强的效果.
关键词:
CdSe量子点
微腔效应
荧光增强 相似文献
4.
The dephasing time of the lowest bright exciton in CdSe/ZnS wurtzite quantum dots is measured from 5 to 170 K and compared with density dynamics within the exciton fine structure using a sensitive three-beam four-wave-mixing technique unaffected by spectral diffusion. Pure dephasing via acoustic phonons dominates the initial dynamics, followed by an exponential zero-phonon line dephasing of 109 ps at 5 K, much faster than the ~10 ns exciton radiative lifetime. The zero-phonon line dephasing is explained by phonon-assisted spin flip from the lowest bright state to dark-exciton states. This is confirmed by the temperature dependence of the exciton lifetime and by direct measurements of the bright-dark-exciton relaxation. Our results give an unambiguous evidence of the physical origin of the exciton dephasing in these nanocrystals. 相似文献
5.
Abdelnasser Aboulfotouh Mohamed Fikry Mona Mohamed Magdy Omar Hossam Rady Yahia Elbashar 《Optical and Quantum Electronics》2018,50(2):115
Characterization of samples of cadmium selenide quantum dots (CdSe) QDs dissolved in toluene colloidal solutions at a concentration of 1.4 mg/ml was carried out through UV–Vis absorption and photoluminescence (PL) spectroscopy. The size-dependent absorption and red-shifted PL emission peak wavelengths could be tuned between 510–576 and 545–606 nm respectively. Optical absorption spectral measurements yielded CdSe QDs having diameters about ~ 2.44–3.69 nm with energy gaps 2.32–2.08 eV which are higher than the bulk CdSe (1.74 eV) reminiscent of quantum confinement. This is found to be in good agreement with the semi-empirical pseudopotential model. In addition, the first excitonic absorption transition 1S(e)1S3/2(h) oscillator strength and the corresponding fluorescence radiative decay time of CdSe QDs are assessed using relevant Einstein relations for absorption and emission in a two-level system. The elaborated calculations would anticipate that the transition oscillator scale with the CdSe QD radius as ~ R2.54. Correspondingly, the calculated radiative decay times decrease from 56.4 to 23.2 ns which scale with CdSe QDs radius as ~ R?2.155 in fairly good agreement with experimental values reported in the literature. 相似文献
6.
Optical performances of reductive glutathione coated CdSe quantum dots were studied under different ageing conditions. The
enhancements of luminescence were obviously occurred for the samples ageing under illumination. The quantum yield of CdSe
was enhanced continuously over 44 days at room temperature, and reached as high as 36.6%. O2 was proved to make a certain contribute to the enhancement. The evolutions of the systems during the ageing time were deduced
according to the variations of pH values with ageing time and the XRD results of the samples ageing in air with illumination.
We conferred that the reduction of surface defects resulted from the photo-induced decomposition of CdSe quantum dots was
the main reason for the enhancement of fluorescence. The production of CdO as a result of the surface reaction with O2 made contributions to the enhancement for a certain extent. The curves of quantum yield versus ageing time were fitted with
a stretched exponential function. It was found that the course of fluorescence enhancement accorded with the dynamics of system
with strongly coupled hierarchical degrees of freedom. 相似文献
7.
V. V. Danilov A. S. Panfutova V. B. Shilov I. M. Belousova G. M. Ermolaeva A. I. Khrebtov 《Optics and Spectroscopy》2014,116(6):941-945
The photodynamics of optical limiting in colloidal solutions of different-size CdSe/ZnS quantum dots is studied. The behavior of the dependences points to a multistage process that includes the bleaching and optical limiting stages. The limiting photodynamics is compared with luminescence dynamics of quantum dots under conditions of high-power excitation. It is shown that the optical limiting efficiency in such media is determined by the position of exciting radiation with respect to the main exciton absorption band of the quantum dot. The roles played by so-called dark states and light quenching in limiting photodynamics are discussed. 相似文献
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V. P. Kochereshko V. N. Kats A. V. Platonov R. A. Suris G. E. Cirlin A. D. Buravlev Yu. B. Samsonenko L. Besombes C. Le Gal H. Mariette 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(5):722-725
The results of a study into the photoluminescence spectra of a set of quantum dots based on GaAs enclosed in AlGaAs nanowires are presented. The steady state and time resolved spectra of photoluminescence under optical excitation both from an array of quantum wires/dots and a single quantum wire/dot have been measured. In the photoluminescence spectra of single quantum dots, emission lines of excitons, biexcitons and tritons have been found. The binding energy of the biexciton in the studied structures was deduced to be 8 meV. 相似文献
9.
Katsuhiro Nose Takahisa Omata Shinya Otsuka-Yao-Matsuo Hideaki Maeda 《Journal of luminescence》2007,126(1):21-26
The role of organic amines in the colloidal synthesis of CdSe quantum dots (QDs) has been studied. CdSe QDs were synthesized from the source solutions containing 5 vol% of amines having various alkyl chain lengths, stereochemical sizes and electron donation abilities. The role of the additional amines was evaluated on the basis of the photoluminescence (PL) properties such as PL wavelength and intensity of the obtained CdSe QDs. The observed PL spectra were explained by the fact that the amines behaved as capping ligands on the surface of the QDs in the product colloidal solution and complex ligands for cadmium in the source solutions. It was shown that the particle size was controlled by the diffusion process depending on the mass and stereochemical shape of the amines, and the luminescence intensity increased with the increasing electron donation ability and capping density of the amines. 相似文献
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R. B. Vasiliev V. S. Vinogradov S. G. Dorofeev S. P. Kozyrev I. V. Kucherenko N. N. Novikova 《Physics of the Solid State》2007,49(3):547-551
The frequencies of the vibrational modes of CdTe and CdSe quantum dots and CdTe/CdSe core/shell nanoparticles prepared by the colloid chemistry method are determined using IR transmission and IR reflection spectroscopy. The experimental IR transmission spectrum of CdTe and CdSe nanocrystals exhibits a broad minimum located between the frequencies of the transverse optical (TO) and longitudinal optical (LO) phonons of bulk CdTe and CdSe crystals. The frequencies of the modes for ensembles of CdTe and CdSe quantum dots are considerably shifted toward lower frequencies as compared to those calculated for single quantum dots. This is explained by the dipole-dipole interaction between quantum dots. The frequencies of modes for the structures with core/shell nanoparticles differ little from the calculated frequencies. This suggests a weakening of the interaction in these structures due to the enhancement of dielectric screening. 相似文献
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H. Nakatani T. Kita O. Kojima O. Wada K. Akahane M. Tsuchiya 《Journal of luminescence》2008,128(5-6):975-977
We have investigated effects of the strain-compensating spacer layer on photoluminescence (PL) properties of excitons in the multilayered self-assembled quantum dots (SAQDs). The PL decay time of excitons in the sample with a thin spacer layer is longer than that with a thick spacer layer. This is attributed to the lowering of the oscillator strengths owing to reduction of the overlap integral between the electrons and holes envelope functions because of spatially extended electron envelope functions in the growth direction. In addition, the PL intensity of the transverse-magnetic mode in the sample with the thinner spacer layer has been found to be enhanced in the polarized PL measurement from the cleaved edge surface of the samples. These results indicate the possibility of QDs connecting along the growth direction via penetration of the electron envelope function. 相似文献
12.
S.C. Dey 《Journal of luminescence》2011,131(12):2707-424
The article reports a green chemical synthesis of colloidal ZnSe quantum dots at a moderate temperature. The prepared colloid sample is characterised by UV-vis absorption spectroscopy and transmission electron microscopy. UV-vis spectroscopy reveals as-expected blue-shift with strong absorption edge at 400 nm and micrographs show a non-uniform size distribution of ZnSe quantum dots in the range 1-4 nm. Further, photoluminescence and electroluminescence spectroscopies are carried out to study optical emission. Each of the spectroscopies reveals two emission peaks, indicating band-to-band transition and defect related transition. From the luminescence studies, it can be inferred that the recombination of electrons and holes resulting from interband transition causes violet emission and the recombination of a photon generated hole with a charged state of Zn-vacancy gives blue emission. Meanwhile electroluminescence study suggests the application of ZnSe quantum dots as an efficient light emitting device with the advantage of colour tuning (violet-blue-violet). 相似文献
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Hua Jin Li-Gong Zhang Zhu-Hong Zheng Xiang-Gui Kong De-Zhen Shen 《Solid State Communications》2004,130(10):653-655
Exciton tunnelling through a ZnSe barrier layer of various thicknesses is investigated in a Zn0.72Cd0.28Se/CdSe coupled quantum well/quantum dots (QW/QDs) structure using photoluminescence (PL) spectra and near resonant pump-probe technique. Fast exciton tunnelling from quantum well to quantum dots is observed by transient differential transmission. The tunnelling time is 1.8, 4.4 and 39 ps for barrier thickness of 10, 15 and 20 nm, respectively. 相似文献
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《Physica E: Low-dimensional Systems and Nanostructures》2011,43(10):2521-2523
Here we report on investigations on CdSe quantum dots incorporated in ZnSe based Schottky photodiodes with near-field shadow masks. Photoluminescence and photocurrent of individual quantum dots were studied as a function of the applied bias voltage. The exciton energy of the quantum dot ground state transition was shifted to the excitation energy by using the Stark effect tuning via an external bias voltage. Under the condition of resonance with the laser excitation energy we observed a resonant photocurrent signal due to the tunnelling of carriers out of the quantum dots at electric fields above 500 kV/cm. 相似文献
16.
Chamarro M. Gourdon C. Lavallard P. Lublinskaya O. Ekimov A. I. 《Il Nuovo Cimento D》1995,17(11):1407-1412
Il Nuovo Cimento D - We have investigated the fine structure of luminecence of CdSe nanocrystals observed with size-selective excitation. We show that the luminescence line closest to the laser... 相似文献
17.
Chamarro M. Gourdon C. Lavallard P. Lublinskaya O. Ekimov A. I. 《Il Nuovo Cimento D》1995,17(11-12):1407-1412
Il Nuovo Cimento D - We have investigated the fine structure of luminecence of CdSe nanocrystals observed with size-selective excitation. We show that the luminescence line closest to the laser... 相似文献
18.
We studied spin states of CdSe quantum dots (QDs) coupled with CdMnSe QDs by probing circular polarization of photoluminescence spectrum under external magnetic fields. The bandgap energies of CdSe and CdMnSe QDs are close to each other and photoluminescence mainly originates from CdSe QDs due to relatively low radiation efficiency of CdMnSe QDs. The photoluminescence lifetime as well as its intensity was decreased with increasing magnetic field, which was ascribed to the increase in the ground state wavefunctions in CdMnSe QDs. The decrease was more pronounced for spin down electrons, which was explained by the difference in spin up and down wave functions under magnetic fields. Our results show that the spin state of CdSe QDs can be manipulated by coupling with CdMnSe QDs. 相似文献
19.
An optical gain plastic, CdSe/PMMA, poly-methyl methacrylate doped with CdSe quantum dot (QD), is reported in this study. With a narrow size distribution of the QD prepared by organic synthesis, the measured results show that the photoluminescence (PL) peak intensity is enhanced by ~2.5 times, FWHM broadened by ~10 nm, and the PL peak wavelength blue shifted by ~25 nm in the CdSe/PMMA compared with plain CdSe QD. Under continuous irradiation of 473-nm laser, the PL peak intensity is positively correlated with time within the first hour after the samples are fabricated, but gradually stabilizes afterward. The obtained results suggest that the CdSe/PMMA material reported here is a desirable optical gain plastic. Potential applications include high gain wideband fiber amplifiers or other photonic devices in the future due to its high flexibility, low weight and low cost. 相似文献