- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
A magnetofluorescent boron-doped carbon dots as a metal-free bimodal probe
摘要： High-resolution observation of biological process is vital for biological researches and diagnosing diseases, which requires accurate diagnosis that involves coordinating imaging technologies such as fluorescence and magnetic resonance (MR). Nowadays, metal-based labels have been used for dual modality imaging. However, heavy metal ions are not environment-and organism-friendly. Therefore, it is a desirable to fabricate a metal-free label with fluorescence and MR properties. Herein, we synthesized boron–doped carbon dots (B–CDs) with dual modal properties through a one-pot solvothermal process. Compared with boron-free CDs, B–CDs exhibited apparent red-shift, higher fluorescence intensity, and higher longitudinal relaxivity (r1 = 5.13 mM-1 s-1). It demonstrated that boron doping can enhance the fluorescence intensity of CDs, and maybe lead to form paramagnetic centers. The fluorescence and MR imaging of B–CDs make them a prospective label for clinical applications as a result of their oversimplified synthesis process, low cost, good biocompatibility and low toxicity. It will open a new window for building novel imaging labels.
关键词： Boron,Magnetic resonance,Fluorescence,Carbon dots
更新于2025-11-14 17:03:37
-
Direct Determination of Ground-State Transition Widths and Natural Level Widths with the Method of Relative Self Absorption
摘要： The method of relative self absorption is based on the technique of nuclear resonance ?uorescence measurements. It allows for a model-independent determination of ground-state transition widths, natural level widths, and, consequently, of branching ratios to the ground state for individual excitations. Relative self-absorption experiments have been performed on the nuclei 6Li and 140Ce. In order to investigate the total level width for the 0+1 , T = 1 level at 3563 keV in 6Li, a high-precision self-absorption measurement has been performed. In the case of 140Ce, self absorption has been applied for the ?rst time to study decay widths of dipole-excited states in the energy regime of the pygmy dipole resonance.
关键词： 6Li,natural level widths,nuclear resonance fluorescence,ground-state transition widths,140Ce,branching ratios,relative self absorption,pygmy dipole resonance
更新于2025-09-23 15:21:21
-
Resonance fluorescence of a single semiconductor quantum dot: the impact of a fluctuating electrostatic environment
摘要： Semiconductor quantum dots are very efficient sources of single and highly indistinguishable photons. These properties rely on the possibility to coherently control the system at the single spin level. At this ultimate level of control, the quantum dot becomes a very sensitive probe of its solid-state environment and any interaction turns into a dephasing process that alters its coherence properties. In this topical review, we give an overview of the issue of charge noise which remains one of the main dephasing mechanisms to overcome. This phenomenon which strongly depends on sample preparation, originates from a fluctuating electrostatic landscape around the quantum dots and renders a unified description quite awkward. We present the common characteristic features induced by charge noise that have been observed in the resonant fluorescence experiments of single quantum dots and discuss the different approaches that have been proposed in the literature to circumvent this problem.
关键词： quantum dots,quantum coherence,optical properties,resonance fluorescence,excitons,III–V semiconductors
更新于2025-09-23 15:19:57
-
Testing requirements for active interrogation systems
摘要： The role of active-interrogation systems for nuclear security is to detect the presence of special nuclear material inside an object by observing the radiation emitted by that object when it has been exposed to known sources of external radiation. Because of the cost, complexity, and the need to avoid irradiating occupants, active-interrogation systems are intended for cargo applications where shielding can prevent detection by passive radiation detection systems. To ensure that active-interrogation systems for detection of special nuclear material are designed and tested to a consistent level of performance, technical standards are needed for evaluating such systems. This paper addresses the testing standards needed for active-interrogation systems to detect high atomic number materials, fissionable materials, and specific special nuclear materials. Because the use of special nuclear material for a testing standard is not practical, this work focuses on the determination of materials that could be used as surrogates in that they provide a similar response as targets of special nuclear materials. The results of this paper, determined through analytic calculations and radiation transport modeling, are based upon scenarios constructed and applied to specific active-interrogation modalities.
关键词： High-Z,Nuclear resonance fluorescence,Active interrogation,Differential die-away,Photofission
更新于2025-09-19 17:15:36
-
Quantification of the Photon Absorption, Scattering, and On-resonance Emission Properties of CdSe/CdS Core/Shell Quantum Dots: Effect of Shell Geometry and Volumes
摘要： Reliable quantification of the optical properties of fluorescent quantum dots (QDs) is critical for their photo-chemical, -physical, and -biological applications. Presented herein is the experimental quantification of photon scattering, absorption, and on-resonance-fluorescence (ORF) activities of CdSe/CdS core/shell fluorescent QDs as a function of the shell sizes and geometries. Four spherical QDs (SQDs) with different diameters and four rod-like QDs (RQDs) with different aspect ratios (ARs) have been analyzed using UV-vis, fluorescence, and the recent polarized resonance synchronous spectroscopic (PRS2) methods. All quantum dots are simultaneous absorbers and scatterers in the UV-vis wavelength region, and they all exhibit strong ORF emission in the wavelength regions where the QDs both absorb and emit. The absorption and scattering cross-sections of the CdS shell are linearly and quadratically, respectively, proportional to the shell volume for both the SQDs and RQDs. However, the effects of CdS shell coating on the core optical properties are different between SQDs and RQDs. For RQDs, increasing the CdS shell volume through the length elongation has no effect on either the peak wavelength or intensity of the CdSe core UV-vis absorption and ORF, but it reduces the QD fluorescence depolarization. In contrast, increasing CdS shell volume in the SQDs induces red-shift in the CdSe core peak UV-vis absorption and ORF wavelengths, and increases their peak cross-sections, but it has no effect on the SQD fluorescence depolarization. The RQD ORF cross-sections and quantum yields are significantly higher than their respective counterparts for the SQDs with similar particle sizes (volumes). While these new insights should be significant for the QD design, characterization, and applications, the methodology presented in this work is directly applicable for quantifying the optical activities of optically complex materials where the common UV-vis spectrometry and fluorescence spectroscopy are inadequate.
关键词： quantum dots,CdSe/CdS,photon absorption,shell geometry,scattering,shell volumes,on-resonance fluorescence
更新于2025-09-19 17:13:59
-
Real-Time Detection of Single Auger Recombination Events in a Self-Assembled Quantum Dot
摘要： Auger recombination is a non-radiative process, where the recombination energy of an electron-hole pair is transferred to a third charge carrier. It is a common effect in colloidal quantum dots that quenches the radiative emission with an Auger recombination time below nanoseconds. In self-assembled QDs, the Auger recombination has been observed with a much longer recombination time in the order of microseconds. Here, we use two-color laser excitation on the exciton and trion transition in resonance fluorescence on a single self-assembled quantum dot to monitor in real-time single quantum events of the Auger process. Full counting statistics on the random telegraph signal give access to the cumulants and demonstrate the tunability of the Fano factor from a Poissonian to a sub-Poissonian distribution by Auger-mediated electron emission from the dot. Therefore, the Auger process can be used to tune optically the charge carrier occupation of the dot by the incident laser intensity; independently from the electron tunneling from the reservoir by the gate voltage. Our findings are not only highly relevant for the understanding of the Auger process, it also demonstrates the perspective of the Auger effect for controlling precisely the charge state in a quantum system by optical means.
关键词： Auger recombination,Resonance fluorescence,Quantum dots,Full counting statistics,Random telegraph signal
更新于2025-09-19 17:13:59
-
GaAs Quantum Dot in a Parabolic Microcavity Tuned to <sup>87</sup> Rb D <sub/>1</sub>
摘要： We develop a structure to efficiently extract photons emitted by a GaAs quantum dot tuned to Rubidium. For this, we employ a broadband microcavity with a curved gold backside mirror which we fabricate by a combination of photoresist reflow, dry reactive ion etching in an inductively coupled plasma and selective wet chemical etching. Precise reflow and etching control allows us to achieve a parabolic backside mirror with a short focal distance of 265 nm. The fabricated structures yield a predicted (measured) collection efficiency of 63 % (12 %), an improvement by more than one order of magnitude compared to unprocessed samples. We then integrate our quantum dot parabolic microcavities onto a piezoelectric substrate capable of inducing a large in-plane biaxial strain. With this approach, we tune the emission wavelength by 0.5 nm/kV, in a dynamic, reversible and linear way, to the Rubidium D1 line (795 nm).
关键词： two-photon resonance fluorescence,strain tuning,microcavity,single-photon source,extraction efficiency,semiconductor quantum dots
更新于2025-09-12 10:27:22
-
Photon Noise Suppression by a Built-in Feedback Loop
摘要： Visionary quantum photonic networks need transform-limited single photons on demand. Resonance fluorescence on a quantum dot provides the access to a solid-state single photon source, where the environment is unfortunately the source of spin and charge noise that leads to fluctuations of the emission frequency and destroys the needed indistinguishability. We demonstrate a built-in stabilization approach for the photon stream, which relies solely on charge carrier dynamics of a two-dimensional hole gas inside a micropillar structure. The hole gas is fed by hole tunneling from field-ionized excitons and influences the energetic position of the excitonic transition by changing the local electric field at the position of the quantum dot. The standard deviation of the photon noise is suppressed by nearly 50% (noise power reduction of 6 dB) and it works in the developed micropillar structure for frequencies up to 1 kHz. This built-in feedback loop represents an easy way for photon noise suppression in large arrays of single photon emitters and promises to reach higher bandwidth by device optimization.
关键词： semiconductor heterostructure,single photon source,two-dimensional hole gas,Quantum dots,quantum optics,resonance fluorescence
更新于2025-09-04 15:30:14