L. Dolgov

Angular shaping of fluorescence from synthetic opal-based photonic crystal

Spectral, angular, and temporal distributions of fluorescence as well as specular reflection were investigated for silica-based artificial opals. Periodic arrangement of nanosized silica globules in the opal causes a specific dip in the defect-related fluorescence spectra and a peak in the reflectance spectrum. The spectral position of the dip coincides with the photonic stop band. The latter is dependent on the size of silica globules and the angle of observation. The spectral shape and intensity of defect-related fluorescence can be controlled by variation of detection angle. Fluorescence intensity increases up to two times at the edges of the spectral dip. Partial photobleaching of fluorescence was observed. Photonic origin of the observed effects is discussed.

Goniometric Setup for Plasmonic Measurements and Characterization of Optical Coatings

Fundamentals of light-induced surface plasmon-polariton waves are considered and implemented on the example of goniometric setup assembled by the authors. The setup was used for investigation of angular dependent light transmittance, reflectance, and fluorescence in dielectric layer containing chromophores. It is explained how optical characteristics of multilayered coatings (thicknesses, refractive indices, and surface roughness) can be deduced from the properties of transmitted and reflected light. Original data about attenuated total internal reflection and plasmon-coupled rare earth fluorescence were obtained. Particularly, angular spectral dispersion and control of Sm3+ fluorescent bands were demonstrated.

Raman and Luminescent Spectra of Sulfonated Zn Phthalocyanine Enhanced by Gold Nanoparticles

Sulfonated Zn phthalocyanine, as a prospective photosensitizer in the photodynamic therapy of tumors, is investigated by means of Raman, infrared, and fluorescence spectroscopies. Conventional and surface-enhanced spectra from this photosensitizer are obtained and compared. Gold nano-islands attached to silica cores (Au-SiO2) are proposed as nanostructures providing plasmonically enhanced signals. Pronounced enhancement of Raman and infrared spectral bands from sulfonated Zn phthalocyanine allows their more convenient assignment with vibrational modes of sulfonated Zn phthalocyanine. In comparison to Raman and IR, the fluorescence is less enhanced by Au-SiO2 particles.

Gilded nanoparticles for plasmonically enhanced fluorescence in TiO2:Sm3+ sol-gel films

Silica-gold core-shell nanoparticles were used for plasmonic enhancement of rare earth fluorescence in sol-gel-derived TiO2:Sm3+ films. Local enhancement of Sm3+ fluorescence in the vicinity of separate gilded nanoparticles was revealed by a combination of dark field microscopy and fluorescence spectroscopy techniques. An intensity enhancement of Sm3+ fluorescence varies from 2.5 to 10 times depending on the used direct (visible) or indirect (ultraviolet) excitations. Analysis of fluorescence lifetimes suggests that the locally stronger fluorescence occurs because of higher plasmon-coupled direct absorption of exciting light by the Sm3+ ions or due to plasmon-assisted non-radiative energy transfer from the excitons of TiO2 host to the rare earth ions.PACS78; 78.67.-n; 78.67.Bf

Vibrational spectra of opal-based photonic crystals

Synthetic silica opals were investigated by infrared and Raman spectroscopies. Vibrational modes associated with molecular groups of opal globules and admixtures were detected. Similarities in Raman and infrared spectra of synthetic opal with reference fused and α-quartz indicate the presence of amorphous phase in opal globules. Also some spectral bands designate on modified optical stretching vibrations at 1000-1200 cm−1 and bigger amount of Si-H defects in photonic crystal.

Modification of light absorption in thin CuInS2 films by sprayed Au nanoparticles

The chemical spray pyrolysis method was used to deposit CuInS2 (CIS) thin films and Au nanoparticles (NPs) in two configurations: glass/Au-NP layer covered with CuInS2 film (Au-NP/CIS) and glass/CuInS2 films covered with Au-NP layer (CIS/Au-NP). According to X-ray diffraction (XRD), the spray of 2 mM HAuCl4 aqueous solution with a volume of 2.5 to 15 ml onto a glass substrate at 340°C results in metallic Au nanoparticles with a similar mean crystallite size in the range of 30 - 38 nm. The mean crystallite sizes remain in the range of 15 - 20 nm when grown onto a CIS film. The prepared films show plasmonic light absorption with increasing intensity in the spectral range of 500- 800 nm when increasing the volume of HAuCl4 solution sprayed. When compared to bare CIS on glass, the absorptance was increased ca. 4.5 times in the case of glass/Au-NP/CIS and ca. 3 times in the case of glass/CIS/Au-NP configuration. The glass/Au-NP/CIS configuration had an advantage since Au-NP could be embedded without chemically damaging the CIS.

Luminescent Imaging of Biological Molecules and Cells on the Photonic Crystal Surface

Photonic crystal based on synthetic opal is considered as an effective substrate for the imaging of DNA and cells without special staining. Luminescent properties of photonic crystals and DNA on the surface of photonic crystals were measured and analyzed. Possible mechanisms of improved DNA imaging caused by light localization effects or energy transfer from the photonic silica host to DNA are discussed.

Sensitizing of Sm3+ fluorescence by silver dopant in the TiO2 films

Composite material based on a TiO2 matrix doped with Sm3+ ions and co-doped with silver was investigated. Samarium ions together with nano- and micro-aggregates of silver were incorporated into the titanium alkoxide during the sol-gel process. Samarium ions were excited either directly (λexc = 488 nm) or through the TiO2 host (λexc = 355 nm). It was revealed that samarium fluorescence (λexc = 488 nm) in gelled TiO2 films is enhanced by up to 20 times in the vicinity of silver inclusions. Sensitizing and plasmonic mechanisms of enhancement in Sm3+ fluorescence are discussed.

Graphene-Enhanced Raman Scattering from the Adenine Molecules

An enhanced Raman scattering from a thin layer of adenine molecules deposited on graphene substrate was detected. The value of enhancement depends on the photon energy of the exciting light. The benzene ring in the structure of adenine molecule suggests π-stacking of adenine molecule on top of graphene. So, it is proposed that the enhancement in the adenine Raman signal is explained by the resonance electron transfer from the Fermi level of graphene to the lowest unoccupied molecular orbital (LUMO) level of adenine.