Spontaneous emission in nanoscopic dielectric particles

We report on theoretical studies of the inhibition of the spontaneous emission process in subwavelength dielectric media. We discuss the modification of the spontaneous emission rate as a function of the size and shape of the medium as well as the position of the emitter in it.     

Spontaneous emission of europium ions embedded in dielectric nanospheres

We measure fluorescence lifetimes of emitters embedded in isolated single dielectric nanospheres. By varying the diameters of the spheres from 100 nm to 2 microm and by modifying their dielectric surrounding, we demonstrate a systematic change of paradigm in the spontaneous emission rate, as we cross the border from the superwavelength regime of Mie resonances to the nanoscopic realm of Rayleigh scattering. Our data show inhibition of the spontaneous emission up to 3 times and are in excellent agreement with the results of analytical calculations.     

Spontaneous organisation of ZnS nanoparticles into monocrystalline nanorods with highly enhanced dopant-related emission

A natural self-assembly process of semiconductor nanoparticles leading to the formation of doped, monocrystalline nanorods with highly enhanced dopant-related luminescence properties is reported. ∼4 nm sized, polycrystalline ZnS nanoparticles of zinc-blende (cubic) structure, doped with Cu⁺-Al³⁺ or Mn²⁺ have been aggregated in the aqueous solution and grown into nanorods of length ∼400 nm and aspect ratio ∼12. Transmission electron microscopic (TEM) images indicate crystal growth mechanisms involving both Ostwald-ripening and particle-to-particle oriented-attachment. Sulphur-sulphur catenation is proposed for the covalent-linkage between the attached particles. The nanorods exhibit self-assembly mediated quenching of the lattice defect-related emission accompanied by multifold enhancement in the dopant-related emission. This study demonstrates that the collective behavior of an ensemble of bare nanoparticles, under natural conditions, can lead to the formation of functionalized (doped) nanorods with enhanced luminescence properties.     

Spontaneous emission between mirrors

The modification of fluorescence lifetimes due to the presence of mirrors is discussed using an image method. The close analogy of this system with that of many-atom cooperative decay is exploited and discussed.     

Spontaneous emission enhancement in metal-dielectric metamaterials

We study the spontaneous emission of a dipole emitter imbedded into a layered metal-dielectric metamaterial. We demonstrate ultra-high values of the Purcell factor in such structures due to a high density of states with hyperbolic isofrequency surfaces. We reveal that the traditional effective-medium approach greatly underestimates the value of the Purcell factor due to the presence of an effective nonlocality, and we present an analytical model which agrees well with numerical calculations.     

Spontaneous emission in micro- and nano-structures

Spontaneous emission of emitters governing the performance of optoelectronic devices is a fundamental phenomenon, and it has strong environment-dependent characteristics. In this article, we mainly review the experimental and theoretical progresses in the control of spontaneous emission by manipulating optical modes with photonic crystals, optical microcavities and metallic nanostructures. The spontaneous emission from emitters in photonic crystals can be modified by the local density of states, and by employing photonic crystals, the devices’ efficiency is enhanced, the angular radiation pattern can be engineered, and highly efficient optoelectronic devices are achieved through decreasing the radiative lifetime. In quantum optical devices, microcavities would alter the lifetime of an excited state through tuning the resonance in the frequency and positioning between the emitters and cavity field, and inducing the emitters to emit spontaneous photons in a desired direction. The emerging enhanced electromagnetic field near metallic nanostructures can help to control and manipulate the spontaneous emission of an emitter. The use of micro- and nano-structures to manipulate spontaneous emission will open unprecedented opportunities for realizing functional photonic devices.     

Spontaneous emission in the near-resonant kapitza-dirac effect

We study the influence of spontaneous emission on atom diffraction by a standing wave laser field. We characterize, analytically, the major regimes of the near-resonant Kapitza-Dirac effect and study, numerically, the influence of spontaneous emission. In particular, we discuss in some detail two important classes of two-beam resonances which are major candidates to develop effective atom beam splitters, the so-called Bragg and Doppleron resonances.     

Silver nanoparticles deposited on dielectric surfaces

Surface plasmon polaritons in nanoparticles were used as a sensitive indicator of structural and electronic properties of metallic nanoparticles deposited upon various dielectric substrates. Quantum size and cluster–substrate interactions were separated. The latter were modelled with the dynamic charge transfer effect. For calibration purposes, the free surfaces of the same clusters exposed to a UHV beam were also investigated. The particles were slightly deformed during deposition; their final shapes and, in particular, their contact areas were determined. The width of the plasmon excitation band was roughly doubled compared to that of the free particles, but proved to depend only slightly on the chemical nature of the substrates, in drastic contrast to the case of fully embedded particles. The analogy holds for the dephasing lifetimes. One reason for this is that the contact area varies strongly with the substrate material, while it is constant in systems of matrix-embedded particles. Received: 26 July 2001 / Revised version: 10 September 2001 / Published online: 15 October 2001     

Generation of excimer emission in dielectric barrier discharges

Dielectric barrier discharges (silent discharges) are used to excite a large number of excimers radiating in the VUV, UV or visible spectral range. The excited species include rare-gas dimers, halogen dimers as well as rare-gas halogen excimers and mercury halogen excimers. In many cases narrow-band UV radiation of typically 1–17 nm halfwidth and remarkable efficiency (1–10%) could be generated. Thus, dielectric barrier discharges provide a simple, versatile arrangement to study the basic reaction kinetics of excimer formation and also bear a substantial potential for large-scale industrial UV processes.     

Spontaneous emission of the non-Wiener type

The spontaneous emission of a quantum particle and superradiation of an ensemble of identical quantum particles in a vacuum electromagnetic field with zero photon density are examined under the conditions of significant Stark particle and field interaction. New fundamental effects are established: suppression of spontaneous emission by the Stark interaction, an additional “decay” shift in energy of the decaying level as a consequence of Stark interaction unrelated to the Lamb and Stark level shifts, excitation conservation phenomena in a sufficiently dense ensemble of identical particles and suppression of superradiaton in the decay of an ensemble of excited quantum particles of a certain density. The main equations describing the emission processes under conditions of significant Stark interaction are obtained in the effective Hamiltonian representation of quantum stochastic differential equations. It is proved that the Stark interaction between a single quantum particle and a broadband electromagnetic field is represented as a quantum Poisson process and the stochastic differential equations are of the non-Wiener (generalized Langevin) type. From the examined case of spontaneous emission of a quantum particle, the main rules are formulated for studying open systems in the effective Hamiltonian representation.     

Spontaneous light emission from fractional-dimensional excitons

We apply the concept of fractional-dimensional excitons to study the process of light emission in quantum confined systems. We focus on a single parameter , known as the degree of dimensionality and which is related to the exciton coherence volume. We compute rates of light emission due to free excitons in GaAs/Al_xGa_1-xAs quantum wells as functions of and link them to experimental observations. The rates are compared with those of quantum well excitons embedded in a microcavity.     

Spontaneous emission from a four-level system

We examine the decay dynamics of a free four-level system in the -V configuration. Quantum interference strongly manifests itself in this system, as can be seen by looking at the combined spectral distribution of the two emitted photons and at the time evolution of the intermediate-level populations, whose effective lifetimes can become very long under certain conditions for the atomic parameters. This effect is attributable to a population transfer mechanism induced in the time evolution equations by the Fano terms, also responsible for the strong modifications of the spectral correlation between the emitted photons which we analyze in detail. Finally, population trapping can also occur when the two intermediate levels are degenerate. Received: 20 October 1998     

Spontaneous emission from a semi-bounded plasma

The electromagnetic radiation field of sources arbitrarily distributed throughout space is found for the case of a semi-bounded plasma when the charged plasma particles are specularly and randomly scattered by the plasma interface. The spectral distributions of the thermal radiation emitted by a nonisothermal semi-bounded plasma into an external medium having a nonzero temperature are calculated.Institute of Theoretical Physics, Ukrainian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, No. 10, pp. 1237–1261, October, 1994.     

Nonlinear absorption in dielectric layers containing copper nanoparticles

The nonlinear absorption in copper nanoparticles contained in glass matrices is investigated using the Z-scan technique at the wavelength of a picosecond Nd: YAG laser (λ=1064 nm). The experimental data obtained for copper nanoparticle-containing composites synthesized through ion implantation are analyzed. It is demonstrated for the first time that, upon exposure to laser radiation at frequencies outside the range of surface plasma resonance, the nonlinear absorption in metallic particles can be caused by the two-photon effect. The optical limiting due to two-photon absorption is discussed for composites containing copper particles.     

Spontaneous and stimulated emission in InAsSb-based LED heterostructures

Electroluminescence of LED heterostructures with active layer made of InAsSb films grown on InAs substrates was studied in the temperature range T = 4.2–300 K. At low temperatures (T = 4.2–100 K), stimulated emission was observed with an optical cavity formed normal to the growth plane. The emission became spontaneous at higher temperatures due to the resonant “switch-on” of the CHHS Auger recombination process in which the energy of a recombining electron-hole pair is transferred to a hole transitioning to the spin-orbit-splitted band. The spontaneous character of emission continued up to room temperature because of the influence of other Auger processes. The results obtained suggest that InAsSb-based LED heterostructures are promising for the fabrication of vertically-emitting mid-infrared lasers.     

Spontaneous emission evaluation in a photonic bandgap microcavity

This work is concerned with an electromagnetic model of a microresonator built in a dielectric periodical structure, with the purpose to achieve the control of spontaneous emission. The aim is to enhance the spontaneous emission into the lasing mode and to reduce it into the continuous spectrum of the nonlasing modes. An example of design of the microcavity structure is presented, together with the evaluation of the β-factor for various operating conditions.     

Millimeter wavelength radiation emission during dielectric aging

The current-voltage characteristic for a metal — thick insulator — metal structure has been investigated by applying high voltage impulses on a variety of industrial insulators. It appears that, in the high field regime (1MV/cm) S-type Negative Differential Conductance may occur, leading to self sustained conductivity oscillations possibly originating in field dependent carrier mobility. The phenomenon is associated with radiation emission during thermalization of hot electrons. Measurements have established the presence of millimeter wavelength radiation during prebreakdown and breakdown stages. The radiation emission intervals within a high-voltage pulse application and response have also been investigated.     

Field electron emission through nonpolar dielectric interface

The probability of electrons penetrating a nonpolar dielectric interface is studied. The lowest probability of potential barrier tunneling is determined in analytical form.