Red/blue shifts of laser-induced fluorescence (LIF) are investigated using several guest dielectric nanoscatterers, such as TiO2, ZnO, Al2O3, and SiO2, in the host Rd6G, RdB, Coumarin 4, and Coumarin 7 ethanolic solutions. A couple of inflection points are identified varying nanoparticle (NP) density into dye solutions based on LIF spectroscopy. The inflection of the spectral shift exhibits that the suspension of NPs in dye solutions significantly involves a couple of competitive chemical and optical mechanisms during photon traveling in scattering media regarding ballistic and diffusive transport. It is shown that the low, medium, and high NP additives in fluorescent suspension induce blue, red, and blue spectral shifts, respectively.
Abstract:The effect of carbon nanostructures such as graphene (G), graphene oxide (GO) and nanodiamond (ND) on the spectral properties of Rhodamine 6G (Rd6G) emission due to the laser induced fluorescence (LIF) was investigated. It is shown that the addition of carbon nanostructures lead to sensible Red/Blue shifts which depend on the optical properties and surface functionality of nanoparticles. The current theories such as resonance energy transfer (RET), fluorescence quenching and photon propagation in scattering media support the experimental findings. Stern-Volmer curves for dynamic and static quenching of Rd6G molecules embedded with G, GO and nanodiamond are correlated with spectral shifts. Furthermore, time evolution of the spectral shift contributes to determine loading/release rates of fluorescent species with large S-parameter on the given nano-carriers.
Angular dependence of the intensity and the emissive wavelength of the laser-induced fluorescence emission in hybrid media (fluorophores+nanoparticles) are investigated using various TiO densities as guest nanoscatterers in the ethanolic solutions of the host Rd6G and coumarin 4 (C4) molecules. It is shown that the intensity of the scattered photons varies in terms of the detection angle. When the nanoscatterer density increases at a certain excitation energy, the angular anisotropy enhances. While the emissive wavelength exhibits the spectral shift in terms of the angular variation for Rd6G fluorophores, it remains invariant for C4-based suspension. In the former case, the emissive wavelength undergoes a spectral shift in terms of angular variation. Several factors such as the optical path length in the scattering media, the excitation volume, and the re-absorption events of the fluorescence emissions by the non-excited molecules strongly affect the spectral features. In fact, the density of the scatterers, the dye concentration, and the interplay between Stokes shift rate and the overlapping between absorption/emission spectra of the given fluorophores are taken into account as the major parameters to form the angular distribution.
This work deals with the fluorescence properties of the methylene blue (MB) fluorophores loaded on metal oxide nanoparticles, such as TiO2, ZnO, and Al2O3 based on laser-induced fluorescence (LIF) spectroscopy. At first, MB is provoked by diode laser at 665 nm, then the fluorescence emissions are recorded using a Czerny-Turner spectrometer. The lucid red shift appears during the right angle LIF measurements of (MB + TiO2NPs) suspensions, where NP are well distributed among the fluorophores. Despite that, the LIF of (MB + TiO2) demonstrates notable red shift in terms of NP concentrations; however, (MB + ZnO) and (MB + Al2O3) exhibit a negligible one. The larger red shift occurs for the NPs with greater refractive indices due to the optical elongation. Furthermore, the quenching coefficients KTiO2, KZnO, and KAl2O3 are measured according to the linear Stern-Volmer formalism. The quenching effect in a (TiO2+MB) attests to be much stronger than that of other nanoparticles of interest. The discrepancy in the fluorescence emissions of MB at the attendance of different metal oxide NPs is very significant during simultaneous imaging/diagnosis and treatment of tumors.
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