Browsing by Author "Guzatov, D. V."

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Open Access
Colloidal photoluminescent refractive index nanosensor using plasmonic effects
(De Gruyter, 2018) Guzatov, D. V.; Gaponenko, S. V.; Demir, Hilmi Volkan
Fluorescence enhancement by metal nanostructures which is sensitive to refractive index n of an ambient medium is suggested as an operation principle of a novel refractive index sensor for liquids. Calculations are made for spherical and spheroidal Ag particles, and potential feasibility of sensitivity of the order of Δn=10-4 is demonstrated. Sensors of this type can be made fully colloidal with metal bodies deposited on a substrate or comprising a metal layer covering colloidal assembly of dielectric particles to serve as a test strip as well as placed on a fiber tip end to get local probing of refractive index in the tip-enhanced refractometry mode. Colloidal core-shell semiconductor nanocrystals may become the best candidates for this type of sensors whereas molecular probes may be affected by chemical properties of tested liquids.
Open Access
Plasmonic enhancement of electroluminescence
(AIP Publishing LLC, 2018) Guzatov, D. V.; Gaponenko, S. V.; Demir, Hilmi Volkan
Here plasmonic effect specifically on electroluminescence (EL) is studied in terms of radiative and nonradiative decay rates for a dipole near a metal spherical nanoparticle (NP). Contribution from scattering is taken into account and is shown to play a decisive role in EL enhancement owing to pronounced size-dependent radiative decay enhancement and weak size effect on non-radiative counterpart. Unlike photoluminescence where local incident field factor mainly determines the enhancement possibility and level, EL enhancement is only possible by means of quantum yield rise, EL enhancement being feasible only for an intrinsic quantum yield Q0 < 1. The resulting plasmonic effect is independent of intrinsic emitter lifetime but is exclusively defined by the value of Q0, emission spectrum, NP diameter and emitter-metal spacing. For 0.1< Q0 < 0.25, Ag nanoparticles are shown to enhance LED/OLED intensity by several times over the whole visible whereas Au particles feature lower effect within the red-orange range only. Independently of positive effect on quantum yield, metal nanoparticles embedded in an electroluminescent device will improve its efficiency at high currents owing to enhanced overall recombination rate which will diminish manifestation of Auger processes. The latter are believed to be responsible for the known undesirable efficiency droop in semiconductor commercial quantum well based LEDs at higher current. For the same reason plasmonics can diminish quantum dot photodegradation from Auger process induced non-radiative recombination and photoionization thus opening a way to avoid negative Auger effects in emerging colloidal semiconductor LEDs.
Open Access
Possible plasmonic acceleration of LED modulation for Li-Fi applications
(Springer New York LLC, 2018) Guzatov, D. V.; Gaponenko, S. V.; Demir, Hilmi Volkan
Emerging LED-based wireless visible light communication (Li-Fi) needs faster LED response to secure desirable modulation rates. Decay rate of an emitter can be enhanced by plasmonics, typically by an expense of efficiency loss because of non-radiative energy transfer. In this paper, metal-enhanced radiative and non-radiative decay rates are shown to be reasonably balanced to get with Ag nanoparticles nearly 100-fold enhancement of the decay rate for a blue LED without loss in overall efficacy. Additionally, gain in intensity occurs for intrinsic quantum yield Q0 < 1. With silver, rate enhancement can be performed through the whole visible. For color-converting phosphors, local field enhancement along with decay rate effects enable 30-fold rate enhancement with gain in efficacy. Since plasmonics always enhances decay rate, it can diminish Auger processes thus extending LED operation currents without efficiency droop. For quantum dot phosphors, plasmonic diminishing of Auger processes will improve photostability.