We found that strong coupling with the cavity can increase Stokes shift of the dye molecules. The experimental finding is qualitatively explained with the simple model based on the splitting of the excited state parabola.
We present the novel metamaterial based on a nanoporous alumina membrane impregnated with R6G dye molecules. The splitting of the reflectance and emission bands at large dye concentration is discussed in terms of strong coupling.
Strong coupling of excitons in macroscopic ensembles of quantum emitters and cavities (or surface plasmons) can lead to dramatic change of the optical properties and modification of the dispersion curves, characterized by the normal mode splitting of the order of 1 eV. Such gigantic alteration of the hybrid energy states enables scores of unparalleled physical phenomena and functionalities, ranging from enhancement of electrical conductivity to control of chemical reactions. While coupling of single emitters to a cavity is a pure quantum mechanical phenomenon, the origin of the strong coupling involving large ensembles of molecules is the subject of controversy. In this work, the strong coupling of rhodamine 6G dye molecules with silver Fabry–Perot cavities is studied and the significant increase of the Stokes shift between the excitation and the emission bands of hybridized molecules is demonstrated. The proposed empirical model of the underlying physics calls for the quantum mechanical parity selection rule.
Harnessing more energy from the sun has led to the development of materials which can efficiently trap the sun radiation in the whole spectrum and re-emit it into a narrow spectral band corresponding to the band gap of a photovoltaic device. The field of metamaterials is largely aimed at designing nanostructured surfaces with tailored absorption (emission) spectra. Many rare-earth doped crystals and glasses can efficiently absorb light throughout the whole visible and near-infrared range of the spectrum and emit radiation at longer wavelengths (1.5 to 3 microns). We report studies of absorption and thermal emission of several rare-earth doped crystals.
In example of Fabry-Perot cavities filled with dye molecules, we studied a range of strong coupling phenomena in complex systems with multiple exciton and optical resonances, bringing applications of these exciting systems one step closer.
Kirchhoff's law of thermal radiation, relating emissivity and absorptance is commonly formulated for opaque bodies in thermodynamic equilibrium with the environment. However, in many systems of practical importance, both assumptions are often not satisfied. We revisit the century-old law and examine the limits of its applicability in an example of Er:YAG and Er:YLF dielectric crystals-potential radiation converters for thermophotovoltaic applications. The (80 at.%) Er:YAG crystal is opaque between 1.45 μm and 1.64 μm. In this spectral range, its absorptance α(λ) is spectrally flat and differentiates from unity only by a small amount of reflection. The shape of the emissivity spectrum ɛ(λ) closely matches that of absorptance α(λ), implying that the Kirchhoff's law can adequately describe thermal radiation of opaque bodies, even if thermodynamic equilibrium is not satisfied. The (20 at.%) Er:YLF crystal had smaller size, lower concentration of Er ions, and it was not opaque. Nevertheless, its spectrum of emissivity had almost the same shape (between 1.45 μm and 1.62 μm) as the absorptance derived from the transmission measurements. Our results are consistent with the conclusion that the Kirchhoff's law of thermal radiation can be extended (with caution) to not-opaque bodies away from the thermodynamic equilibrium.
Nanoparticle-based fluorescence DNA/RNA sensing offers promising applications in both research and medical diagnosis due to the ease of surface chemical modification and sample handling, allowing detection in complex media. The performance of the conventional fluorescence biosensors is often limited by the insufficient fluorescence signal. To overcome the disadvantage, we advanced silver-coated magnetic nanoparticles with strong plasmon resonance to enhance the molecular beacon (MB)-based nucleic acid nanosensors. The silver-coated magnetic nanoparticles were chemically synthesized to compose of 20 nm iron oxide magnetic nanoparticle core and 60 nm thick Ag coating, forming iron oxide/Ag core-shell nanoparticles. Fluorescently labeled DNA MBs were immobilized on the Ag surface which serves as the quencher for the closed MBs and provides fluorescence enhancement for the unfolded MBs in the presence of the complementary target sequence. More importantly, the improved Ag shell mitigates the strong optical absorbance in the visible range associated with the magnetic nanoparticles increasing the fluorescence intensity. The detection was performed by dispersing the nanosensors in a 20 μl analyte solution for 10 minutes for accelerated target capture through 3D diffusion and concentrating them magnetically for enhanced fluorescence signal acquisition. The rapid, label-free DNA detection resulted in a detection limit of 10 pM target DNA.
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