China
Africa
Explore chapters and articles related to this topic
Fluorescence Microscopy
Published in Bethe A. Scalettar, James R. Abney, Cyan Cowap, Introductory Biomedical Imaging, 2022
Bethe A. Scalettar, James R. Abney, Cyan Cowap
The existence of a Stokes shift is pivotally important to fluorescence microscopy. In particular, the shift allows the fluorescence signal to be viewed superimposed on a dark background, which markedly enhances the sensitivity of fluorescence microscopy (Fig. 6.1). A dark background is generated by excluding the shorter wavelength excitation from the detector using a filter (Section 6.3.2).
Luminescent Nanomaterials: A Step Towards Solid-State Lighting and Display
Published in Odireleng Martin Ntwaeaborwa, Luminescent Nanomaterials, 2022
Mohan Lal Meena, Sudipta Som, Chung-Hsin Lu, Somrita Dutta, Rajan Kumar Singh, Shawn D. Lin
The variation in emission band and absorption band is known as Stokes shift. The reabsorption effect is strongly related tothe Stokes shift values. In general, traditional QDs shows average 40 meV Stokes shift for Cd based QDs. While Brennan et al. [29] showed Stokes shift in the range of meV for PQDs with size variation in 12 nm to 4 mm. The PLQY of the QDs decreases with auger recombination of charged excitons. The average auger lifetime is found tobe shorter 30–100 than single excitons. The general principal of auger recombination suggests that non-radiative energy transfer to the nearby charge carriers rather than converting into a photon. The PLQY and decay dynamics can easily explain using various optical characterization techniques such as blinking, transient absorption, and time resolved PL spectroscopy [30, 31]. Hence, a detailed explanation of exciton behavior is needed for the application of PQDs in LEDs.
Interfacial Kinetics and Hopping Transitions
Published in Juan Bisquert, The Physics of Solar Energy Conversion, 2020
For a photon-induced transition, commented above, the molecule changes suddenly in the vertical transition, as indicated in Figure 6.9. Just after absorption, the “hot” electron-molecule system is in the nuclear configuration of the ground state, and then relaxes to the bottom of the potential well of the excited state by an amount corresponding to the reorganization energy. Subsequently, the molecule may decay to the ground state by emitting a photon that is red shifted with respect to the maximal absorbance, and subsequently followed by a relaxation again by the energy λ. This is the process of fluorescence, and the relative displacement of the absorption and emission spectra is termed a Stokes shift.
Computational study of optoelectronic properties of oxadiazole-based compounds for organic light emitting diodes
Published in Molecular Physics, 2022
Rabah Hebbali, Sidi Mohamed Mekelleche, Lamia Kara Zaitri
Using TD-PBE0/6-31G(d,p) singlet excited state geometries, TD-PBE0/6-31G(d,p) calculations in DMF were performed to predict the fluorescence properties of compounds 1–8, Table 4 lists the energies of fluorescence transitions Eflu, fluorescence wavelengths λflu, major MO contributions, and oscillator strengths fflu for the lowest singlet excited states S1.The calculated emission wavelength value (405 nm) of 1 agrees quite well with the experimental values (367 nm) obtained by Chen et al. [88]. The obtained results show that, for the fluorescence phenomenon, the LUMO→HOMO electronic transitions the most important contribution for all derivatives 1–8. The oscillator strengths, ranging from 0.93 to 2.24, show strong fluorescence intensities for all derivatives 1–8. On the other hand, the large Stokes shift (SS) is useful in practice because it can lessen self-quenching caused by molecule self-absorption. A Stokes shift indicates the loss of energy between absorption and emission. According to the obtained results (Table 4), the designed fluorophores 6 and 8, which have the highest SS values of the studied series, may be used such as light-emission layers and building blocks in OLED devices.
Coherence-enhanced diffusion filtering applied to partially-ordered fluids
Published in Molecular Physics, 2020
Perry W. Ellis, Jyothishraj Nambisan, Alberto Fernandez-Nieves
Fluorescence is an inelastic process where a material absorbs and then re-emits light; the initial absorption excites a singlet state in the material which then decays via photon emission [17]. The absorption and emission are characterised by their respective spectra, with the peak in the emission spectrum occurring at a longer wavelength than the peak in the absorption spectrum. As a historical aside, the realisation that this process consists of both absorption and emission of light is attributed to Stokes, as is the name ‘fluorescence’ itself [18,19]. This is the reason that the difference in the peak of the excitation and emission spectra for a given fluorophore is known as the ‘Stokes shift’ [17]. A standard epifluoresence setup takes advantage of this with a dichroic mirror and pair of band-pass filters centred on the peaks in the excitation and emission spectra, with no overlap in the transmitted wavelengths of the filters. Consequently, the light passed by these filters is referred to as the excitation light and emission light, respectively. The dichroic mirror typically reflects the excitation light and passes the emission light. Thus, the sample can be illuminated by the excitation light, exciting the fluorophores in the sample, with only the emission light collected on the detector, typically a CCD camera. Imaging the active nematic with such a setup results in signal coming from only the fluorescently labelled microtubules, clearly revealing the nematic structure, as shown in the example image in Figure 1(D). This is a wide-field technique, meaning that even though only a specific plane in the sample is in focus, light from out of focus planes can still reach the detector.