Effect of Spheroidal Nanoparticles on the Fluorescence of Dye Molecules and Adsorbed MEH–PPV Macrochains in Solutions

Anisotropic properties of aspherical nanoparticles make it possible to significantly expand their spectral-optical applications associated with local field effects. The plasmon resonance characteristics of such particles have additional features that conductive nanoglobules do not possess. The results of synthesis and morphological analysis of ellipsoidal hematite nanoparticles coated with a gold shell and spherical magnetite nanoparticles by atomic force microscopy are presented. The absorption spectra of aqueous solutions of such nanoparticles, as well as conductive nanoparticles with chain molecules adsorbed on them, are obtained. Based on the methods of dynamic light scattering, histograms of particle size distribution are constructed. The influence of spheroidal magnetic nanoparticles coated with a gold shell on the luminescence intensity of molecules of an organic dye (fluorescein) and poly[2-methoxy-5(2'-ethylhexyloxy)-1,4-phenylenevinylene] is studied. An increase in the luminescence intensity of both types of luminophors at certain concentrations of metallized spheroidal nanoparticles is detected. A mathematical model of radiative and nonradiative processes in the studied colloidal system is presented, as well as the results of calculations of spectral and velocity characteristics based on well-known applied FDTD packages. Characteristic graphs are constructed for the spectral density of the number of photons emitted at a certain frequency of the combined system “molecule–nanoparticle” for various positions of the nanoparticle relative to the molecule and two characteristic directions of the transition dipole moment vector. The relationship between the frequencies of two plasmon resonances and the eccentricity of the spheroid revealed in the model is clearly manifested in the obtained spectral curves. The closer the spheroid eccentricity to 0, the smaller the frequency interval between two spaced plasmon resonance peaks, which merge into a single spectral band at zero eccentricity. The results obtained can be used in the development and modification of sensors with an adjustable conformational structure of macrochains, such as luminescent optical testers for the concentration of molecular oxygen (including singlet oxygen) and chemical sensors based on the effects of surface plasmon resonance and surface-enhanced Raman scattering.