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Excimer based FRET between non-FRET pair flourophores aided by the aromatic moiety of anionic surfactants: An experimental observation
摘要： A new FRET pair has been reported based on the apperance of excimeric emission and hence significant spectral overlap between an otherwise non-FRET pair fluorophores viz pyrene and rhodamine 6G in the anionic sodiumdodecylbenzenesulfonate (SDBS) micellar system. The occurence of FRET based on such modulation of spectral overlap integral has not been dealt with in detail in comparison to the other FRET parameters like distance between the fluorophores and orientation. Due to the presence of benzene ring in the SDBS micellar system the formation of excimers is augemented due to the π?π interactions between the pyrene molecules and the benzene units of the surfactants. The excimeric pyrene has a bathochromically shifted peak which overlaps with the absorption peak of rhodamine 6G thereby giving rise to energy transfer as FRET between these otherwise non-FRET pair molecules. The efficiency of FRET between the pyrene and rhodamine 6G can be modulated by the degree of spectral overlap between the excimeric peak of pyrene and the absorption peak of rhodamime6g. All the experiments were carried in the Sodiumdodecylsulfate (SDS) micellar system also, which unlike SDBS does not possess any benzene unit, in order to compare the results of excimer formation as well the FRET process.
关键词： rhodamine 6G,Pyrene,overlap integral,Excimer,FRET
更新于2025-11-19 16:46:39
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Impact of Stokes Shift on the Performance of Near-Infrared Harvesting Transparent Luminescent Solar Concentrators
摘要： Visibly transparent luminescent solar concentrators (TLSC) have the potential to turn existing infrastructures into net-zero-energy buildings. However, the reabsorption loss currently limits the device performance and scalability. This loss is typically defined by the Stokes shift between the absorption and emission spectra of luminophores. In this work, the Stokes shifts (SS) of near-infrared selective-harvesting cyanines are altered by substitution of the central methine carbon with dialkylamines. We demonstrate varying SS with values over 80 nm and ideal infrared-visible absorption cutoffs. The corresponding TLSC with such modification shows a power conversion efficiency (PCE) of 0.4% for a >25 cm2 device area with excellent visible transparency >80% and up to 0.6% PCE over smaller areas. However, experiments and simulations show that it is not the Stokes shift that is critical, but the total degree of overlap that depends on the shape of the absorption tails. We show with a series of SS-modulated cyanine dyes that the SS is not necessarily correlated to improvements in performance or scalability. Accordingly, we define a new parameter, the overlap integral, to sensitively correlate reabsorption losses in any LSC. In deriving this parameter, new approaches to improve the scalability and performance are discussed to fully optimize TLSC designs to enhance commercialization efforts.
关键词： transparent luminescent solar concentrators,overlap integral,reabsorption loss,Stokes shift,near-infrared harvesting
更新于2025-09-23 15:21:01
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Determining the Waveguide Profile using the Overlap Integral
摘要： The determination of the index pro?le in guiding structures is a central problem in applied photonics, ranging from optical ?bers to femtosecond-written waveguides. A non-destructive and relatively easy method consists in the measurement of the index pro?le by measuring the transmitted ?eld. From the transmitted ?eld, the refractive index pro?le is computed by direct inversion of the Helmholtz equation. This technique is called near-?eld method. Here we present a new near-?eld method based upon the inversion of the overlap integral. From the waveguide theory, the power coupled to the m-th mode with pro?le ψm(x) from an input Ein(x) is am = (cid:2) Ein(x)ψ ? (x)dx. If the input Ein(x) is shifted by an amount x0, the overlap am(x0) is the convolution between the pro?le of the input beam Ein and the mode pro?le ψm. The convolution operator implicitly ?lters out the noise, but without creating distorsions or artifacts. An experimental measurement of the transmitted ?eld Eexp will be Nη, where η is a white Gaussian noise and N the noise amplitude. In the previous formulae P is the overall power given by |am(x0)|2. If both amplitude and phase of the transmitted ?eld are simultaneously measured, the overlap am can be inverted for any guided mode m. If only the intensity is measured, the overlap can be inverted only if the waveguide is monomodal. An example of the reconstructed mode in the case of intensity-only measurements is plotted in Fig. 1(a) for ψ0 = cosh(x/w) with w/λ = 4 and N/P = 1 × 10?4. The retrieved ?eld is very close to the exact one, with appreciable differences only for |x/λ | > 10. Important to stress, this range is larger than what it is achievable with a single direct measurement of the transmitted ?eld. The next step is to invert the Helmholtz equation, that is, to compute the second derivative of the retrieved mode. Direct application of the inversion protocol strongly enhances the noise, above all on the tails of the mode. The net result is the appearance of several fake oscillations, even where the retrieval of the mode is good. The problem can be overcome by ?tting the mode tails with a decaying exponential, in accordance with the waveguide theory. The reconstructed guide pro?les shown in Fig. 1(b) do not present arti?cial oscillations on the tails, showing a 10% error with respect to the original waveguide, the error depending slightly on the original signal-to-noise ratio N/P.
关键词： refractive index,overlap integral,Helmholtz equation,waveguide profile,near-field method
更新于2025-09-11 14:15:04