K. V. Bogdanov

Luminescent isolated diamond particles with controllably embedded silicon-vacancy colour centres

A technique to fabricate isolated diamond particles with controllably embedded silicon-vacancy (Si-V) colour centres is described. Particle growth and Si doping are performed by microwave plasma-enhanced chemical vapour deposition (CVD) using silane as a source of impurity atoms. The Si-V centres have a strong narrow-band photoluminescence (PL) at room temperature. The dependence of PL intensity of the 738 nm zero-phonon line (ZPL) on silane concentration in the feed-gas mixture exhibits a pronounced maximum. A comparison of the PL and Raman spectra shows that there is an evident correlation between the ZPL intensity and the presence of structural defects and nondiamond carbon phases that act as nonradiative recombination centres suppressing radiative recombination. The results open the door for using the powerful CVD technique for large-scale production of photostable near-infrared single-photon emitters and noncytotoxic biomarkers.

Comparative analysis of Raman spectra of PbS macro- and nanocrystals

A comparative analysis of the Raman spectra of bulk PbS and PbS nanocrystals with average diameters of 6.6 and 3.8 nm has been performed. It is shown that the bands due to the LO phonons at the Γ point of the Brillouin zone dominate in the first- and second-order Raman spectra of the nanocrystals. Based on the analysis of the relative band intensities for the first- and second-order spectra a qualitative conclusion is drawn: the electron-LO-phonon interaction in PbS nanocrystals increases with a decrease in their size.

Chemical vapor deposition of isolated spherical diamond particles with embedded silicon-vacancy color centers onto the surface of synthetic opal

Isolated spherical diamond particles with embedded silicon-vacancy color centers are synthesized on a patterned surface of synthetic opal by chemical vapor deposition methods. The phase composition of the particles is determined and their structural and luminescence properties are studied. Prospects are discussed for the application of these particles as integrated spherical diamond microcavities, in which color centers are situated directly in the microcavities.

Size-dependent Raman and SiV-center luminescence in polycrystalline nanodiamonds produced by shock wave synthesis

Size-dependent structural and luminescent properties of the diamond polycrystals produced by shock wave synthesis followed by grinding and separation into fractions of different polycrystal median sizes (25–1000 nm) are studied by comparative Raman and luminescence spectroscopy. The intense 738 nm narrow band luminescence of the SiV-centers are observed for all fractions. The SiV luminescence intensity has a maximum at the median size of about 180 nm that is controlled by competition between deactivation of the SiV-centers by defects in the diamond nanocrystal lattice and that controlled by nonradiative recombination centers in the volume of the intergranular layers.

Whispering gallery modes in a spherical microcavity with a photoluminescent shell

Whispering-gallery mode spectra in optical microcavities based on spherical silica particles coated with a thin photoluminescent shell of hydrogenated amorphous silicon carbide are studied. The spectral positions of the whispering-gallery modes for spherical microcavities with a shell are calculated. The dependence of the spectral distance between the TE and TM modes on the shell thickness is examined.

Quantum dots - graphene hybrid structures: interplay of optical and electrical properties

We investigate electrical photoresponse of multilayer graphene decorated with CdSe/ZnS quantum dots. It was found that photoresponse of these hybrid structures depends on quantum dot photoluminescence quantum yield. We demonstrate in uence of external factors (light exposure and treatment with ammonia vapors) on photoluminescence quantum yield of quantum dots and electrical photoresponse of the hybrid structures.

Highly intensive emission of the NV− centers in synthetic HPHT microdiamonds at low nitrogen doping

Synthetic high-pressure high-temperature (HPHT) microdiamonds demonstrate strong resonant-like enhancement of the NV− photoluminescence (PL) at unexpectedly low concentration of the substitutional nitrogen atoms (NS) of 90 ppm, which is significantly smaller than the ∼250 ppm characteristic for conventional HPHT synthesis. The EPR, Raman, and luminescent spectroscopies, including time-resolved PL, provide evidence that this is due to competition between the increase in PL with increasing concentration of the NV− centers and nonradiative deactivation of these centers by defects induced by the NS in the diamond crystal lattice. It is suggested that the intensity of the NV− center emission can be optimized by the appropriate choice of nitrogen doping concentration which does not substantially disrupt the diamond crystal lattice.Synthetic high-pressure high-temperature (HPHT) microdiamonds demonstrate strong resonant-like enhancement of the NV− photoluminescence (PL) at unexpectedly low concentration of the substitutional nitrogen atoms (NS) of 90 ppm, which is significantly smaller than the ∼250 ppm characteristic for conventional HPHT synthesis. The EPR, Raman, and luminescent spectroscopies, including time-resolved PL, provide evidence that this is due to competition between the increase in PL with increasing concentration of the NV− centers and nonradiative deactivation of these centers by defects induced by the NS in the diamond crystal lattice. It is suggested that the intensity of the NV− center emission can be optimized by the appropriate choice of nitrogen doping concentration which does not substantially disrupt the diamond crystal lattice.

Transparent glass-ceramics with Yb3+,Ho3+:YNbO4 nanocrystals for green phosphors

We report on synthesis, structure, Raman and optical spectroscopy of transparent glass-ceramics (GCs) containing nanocrystals of rare-earth orthoniobates, Yb3+,Ho3+:YNbO4 and β-quartz solid solution. Under the near-IR excitation, the GCs exhibit intense upconversion luminescence which color properties can be tuned by the heat-treatment regime due to the structural changes in the orthoniobate nanocrystals. The developed GCs are promising as thermal shock resistant green phosphors.

Nanocarbons and quantum dots formation in new hybrid materials

We present technique of obtaining complex hybrid structures combining the multi-walled carbon nanotubes or multi-layer graphene and luminescent hydrophobic semiconductor core/shell quantum dots CdSe/ZnS. As a result, a formation of quantum dot decorated carbon nanotubes and graphene films is evidenced by 2D microluminescence and micro-Raman mapping of quantum dots and nanocarbons, respectively, where a spatial correlation between the luminescence and Raman signals is found.