Sergei Musikhin

Size-tunable infrared (1000–1600 nm) electroluminescence from PbS quantum-dot nanocrystals in a semiconducting polymer

Nanocomposites consisting of PbS nanocrystals in a conjugated polymer matrix were fabricated. We report results of photo- and electroluminescence across the range of 1000 to 1600 nm with tunability obtained via the quantum-size effect. The intensity of electroluminescence reached values corresponding to an internal quantum efficiency up to 1.2%. We discuss the impact of using different-length capping ligands on the transfer of excitations from polymer matrix to nanocrystals.

Efficient excitation transfer from polymer to nanocrystals

We quantify experimentally the efficiency of excitation transfer from a semiconducting polymer matrix to quantum dot nanocrystals. We study 5±0.5 nm PbS nanocrystals embedded in MEH-PPV (poly[2-methoxy-5-(2′-ethylhexyloxy-p-phenylenevinylene)]) polymer. We determine the excitation transfer efficiency from normalized photoluminescence excitation measurements. When the composites are made using as-synthesized PbS nanocrystals capped by oleate ligands, the excitation transfer efficiency is about 20%. Replacing these ligands with shorter chains results in a factor-of-3 enhancement in the excitation transfer efficiency. Our findings provide guidance to the realization of efficient electroluminescent devices.

Luminescence from processible quantum dot-polymer light emitters 1100–1600 nm: Tailoring spectral width and shape

Electroluminescent devices combining two families of PbS colloidal quantum dots to achieve spectrally tailored two-color emission are reported. Depending on device structure selected—the use of two separated layers versus a mixture of nanocrystals—the structures demonstrated light emission either in two infrared frequency peaks corresponding to the spectral region 1.1–1.6 μm or in a wide band spanning this same spectral region. Separated-layer devices exhibit wide tunability in the relative intensity of the two peaks by varying excitation conditions. Replacing oleate with octodecylamine ligands increases the internal electroluminescence efficiency to 3.1%.

An extended cavity diode-pumped femtosecond Yb:KGW laser for applications in optical DNA sensor technology based on fluorescence lifetime measurements

A reliable and power-scalable extended cavity diode-pumped passively mode-locked Yb:KGW laser generating ~200 fs long pulses at a repetition rate of 15 MHz was developed and characterized. The laser delivered up to 150 mW of average power at fundamental wavelength of 1040 nm, corresponding to a pulse energy of 10 nJ. The laser radiation was frequency-doubled in a single pass configuration within a nonlinear BIBO crystal to produce femtosecond green radiation at 520 nm with peak power of ~200 W. The generated second harmonic served as excitation source for optical DNA biosensor based on fluorescence lifetime measurements obtained using the time-correlated single photon counting technique.

Luminescent properties and electronic structure of conjugated polymer-dielectric nanocrystal composites

We report results of experimental investigations of the luminescent properties of two different conjugated polymers in which we embedded nanocrystals of Al2O3, Y2O3, ZnO, and SnSbO. The dielectric nanocrystals result in a blueshifting and broadening of luminescence spectra of poly(p-phenylene vinylene) with a simultaneous disappearance of its vibronic structure. The same nanocrystals in a poly[2-(6-cyano-6′-methylheptyloxy)-1,4-phenylene] matrix cause redshifting and spectral broadening. These observations are explained by referring to a model that accounts for the change in the polarization component of the carrier and exciton energy in the vicinity of inclusions.

Polarization memory in a system of CdSe nanorods

Polarization characteristics and spectra of photoluminescence in CdSe nanorods suspended in liquid were investigated. Experiments demonstrated the presence of the polarization memory related to the mismatch of nanorods and solvent dielectric constants, as well as to anisotropy of optical matrix elements. Luminescent spectra contained two peaks corresponding to interband transitions between the ground and excited size-quantized states and having essentially different values of polarization memory, presumably due to different anisotropy of corresponding matrix elements. The amplitude of polarization memory decreased with the increase in concentration of nanorods confirming the hypothesis of their mutual influence.

Influence of nanocrystals on the energy levels and luminescent properties of the polymer matrix in conjugated polymer–dielectric nanocomposites

Abstract We report results of experimental investigations into the luminescent properties of conjugated polymers in which are embedded dielectric nanocrystals. In poly( p -phenylene vinylene), embedding nanocrystals results in a blue shift and broadening of luminescence spectra with a simultaneous disappearance of its vibronic structure. The same nanocrystals in poly(2-(6-cyano-6 ′ -methylheptyloxy)-1,4-phenylene) cause a red shift and spectral broadening. The results are explained with reference to a model accounting for the change in the polarization component of carrier and exciton energy in the vicinity of nanocrystals. The polymer–dielectric nanocomposites demonstrated increased electroluminescence effectiveness compared with pure polymers.

Fabrication and investigation of nanocomposites of conducting polymers and GaSb nanocrystals

Nanocomposites consisting of GaSb nanocrystals in conducting polymer matrices were fabricated and investigated. Optical absorption and electrical properties of the samples were analyzed. Electroluminescence with a spectral maximum near 1600 nm was observed for both bias polarities. Infrared electroluminescence from GaSb/polymer nanocomposites points to possible applications in fibre-optic communications.

Toward the development of optical nucleic acid biosensors based on TIRF and TCSPC for high sensitivity determinations

The results of preliminary investigations toward the design of an optical biosensor instrument for the selective and direct analysis of low copy numbers of target nucleic acids in native form are reported. A concept development prototype was constructed based on a total internal reflection fluorescence (TIRF) configuration and the use of time correlated single photon counting (TCSPC). Selective detection of interfacial hybrid formation was done by identification of luminescence of characteristic (20ns) lifetime from the intercalant fluorophore ethidium bromide associated with nucleic acid hybrids formed at the interaction surface of optical sensor elements. Results of these investigations suggest that detection limits on the order of 107 dye:dsDNA complexes can be achieved when an effective sensor interaction surface of 150 µm diameter is used. The presence of interfacial nucleic acid duplexes at a sensor surface was further verified by thermal denaturation studies. The sensitivity of this concept design prototype was found to be most limited by long lifetime fluorescence intrinsic to the detection optics in conjunction with large amounts of scatter dispersed from the sensor cartridge. Future directions for continued device development are discussed.

Development of femtosecond Yb:KGW laser for applications in optical DNA sensor technology

We report on development of frequency-doubled diode-pumped ultrashort pulse Yb:KGW laser operating at 520 nm with approximately 200 fs long pulses at a repetition rate of 15 MHz. For ~2 W of absorbed pump power at 980 nm, the laser delivers up to 30 mW of average power at fundamental wavelength of 1040 nm, corresponding to a pulse energy of 2 nJ. The laser radiation was then frequency-doubled in a single pass configuration within a nonlinear BIBO crystal to produce femtosecond green radiation at 520 nm with peak power of ~200 W. The generated second harmonic served as excitation source of optical DNA sensor based on fluorescence lifetime measurements using the time correlated single photon counting (TCSPC) technique.