Plasmon-enhanced ultraviolet photoluminescence from the hybrid plasmonic Fabry-Perot microcavity of Ag/ZnO microwires

Exciton-polariton light-emitting diode based on a single ZnO superlattice microwire heterojunction with performance enhanced by Rh nanostructures

One-dimensional (1D) wirelike superlattice micro/nanostructures have received considerable attention for potential applications due to their versatility and capability for modulating optical and electrical characteristics. In this study, 1D superlattice microwires (MWs), which are made of undoped ZnO and Ga-doped ZnO with periodic and alternating crystalline layers (ZnO/ZnO:Ga), were synthesized individually. Under optical excitation, a series of resonance peaks in the photoluminescence spectrum can be ascribed to polariton emission, which originates from the coupling interaction of the 1D photonic crystal and confined excitons along the wire direction. Using a p-type GaN layer as the hole transport layer, a kind of waveguide light source based on an individual ZnO/ZnO:Ga superlattice MW was proposed and constructed. By analysing the spatially resolved electroluminescence spectra, the observed multipeak was ascribed to exciton-polariton emission with a vacuum Rabi splitting of about 275 meV. Cladding with Rh nanostructures gives rise to appropriate ultraviolet plasmons, and the Rabi splitting energy of our device was enhanced up to 413 meV. The exciton-polariton properties were further examined using angle-resolved electroluminescence measurements. Therefore, individual superlattice MWs can act as optical microresonators to achieve photon-exciton coupling with a large Rabi splitting energy. The experimental results indicate that an individual ZnO/ZnO:Ga superlattice MW can be generally used in developing exciton-polariton luminescence/lasing light sources, particularly for constructing low-threshold/thresholdless lasers toward pragmatic applications.

Emerging transparent conducting oxides material: 2-dimensional plasmonic Zn doped CuGaO2 nanoplates for Q-switched fiber laser

A passively Q-switched Er³⁺ doped fiber laser has been realized by using Zn doped hexagonal CuGaO₂ (CGZO) nanoplates (NPs) as a saturable absorber (SA) for the first time. The CGZO NPs SA film exhibits strong saturable absorption property, meanwhile with a small nonsaturable loss of 5.179%, and the modulation depth is up to 40.821%. A stable passively Q-switched laser, which was centered at 1559.75 nm, was achieved, and the threshold was as low as 42 mW. With an increase of the pump power from 42mW to 361mW, the pulse duration decreases from 36 μs to 1.71 μs, and the maximum output power of 12.1 mW is achieved. Particularly, the optical-optical conversion efficiency of the Q-Switched laser based on CGZO NPs reached 3.76%. Due to whispering-gallery-mode (WGM) resonance in CGZO NPs, the nonlinear optical response of CGZO NPs has been enhancement. These findings demonstrate that CGZO NPs are promising SA for fabricating high-efficiency and low-threshold pulse lasers.

Wavelength-Tunable Waveguide Emissions from Electrically Driven Single ZnO/ZnO:Ga Superlattice Microwires

Because of the superlattice structures comprising periodic and alternating crystalline layers, one-dimensional photon crystals can be employed to expand immense versatility and practicality of modulating the electronic and photonic propagation behaviors, as well as optical properties. In this work, individual superlattice microwires (MWs) comprising ZnO and Ga-doped ZnO (ZnO/ZnO:Ga) layers were successfully synthesized. Wavelength-tunable multipeak emissions can be realized from electrically driven single superlattice MW-based emission devices, with the dominant wavelengths tuned from ultraviolet to visible spectral regions. To illustrate the multipeak character, single superlattice MWs were selected to construct fluorescent emitters, and the emission wavelength could be tuned from 518 to 562 nm, which is dominated by Ga incorporation. Especially, by introducing Au quasiparticle film decoration, emission characteristics can further be modulated, such as the red shift of the emission wavelengths, and the multipeaks were strongly modified and split into more and narrower subbands. In particular, electrically pumped exciton-polariton emission was realized from heterojunction diodes composed of single ZnO/ZnO:Ga superlattice MWs and p-GaN layers in the blue-ultraviolet spectral regions. With the aid of localized surface plasmons from Au nanoparticles, which deposited on the superlattice MW, significant improvement of emission characteristics, such as enhancement of output efficiencies, blue shift of the dominant emission wavelengths, and narrowing of the spectral linewidth, can be achieved. The multipeak emission characteristics would be originated from the typical optical cavity modes, but not the Fabry-Perot mode optical cavity formed by the bilateral sides of the wire. The resonant modes are likely attributed to the coupled optical microcavities, which formed along the axial direction of the wire; thus, the emitted photons can be propagated and selected longitudinally. Therefore, the novel ZnO/ZnO:Ga superlattice MWs with a quadrilateral cross section can provide a potential platform to construct multicolor emitters and low-threshold exciton-polariton diodes and lasers.

Reverse-bias-driven whispering gallery mode lasing from individual ZnO microwire/p-Si heterojunction

In this paper, electrically driven whispering gallery mode (WGM) lasing was observed from ZnO single microwire (SMW)/p-Si heterojunctions operated at reverse bias. Current-voltage curve exhibits a non-ideal rectification characteristic with a turn-on voltage of about 0.8 V. When the reverse current of 20 mA was applied, several sharp lasing peaks with FWHM as narrow as ∼2 nm appeared in the spectra, which demonstrated that the gain was now large enough to enable the cavity resonant in ZnO SMW. The resonant process, lasing mode and quality factor (Q) were investigated via experiments and theory. The observed discrete lasing peak positions effectively matched the simulated lasing modes. The carrier transport process and light emission mechanism in heterojunctions are also discussed by energy band theory and interface defect.

Plasmonic microcavity using photo-reduced silver nanoparticles and light-emitting polymer

We report a plasmonic Fabry-Perot (F-P) microcavity with silver nanoparticles and a continuous silver film function as the end mirrors, where the silver nanoparticles were produced through photo-reduction. Filled with a layer of light-emitting polymer, the F-P microcavity becomes an active device with its output spectrum dependent on localized surface plasmon resonance (LSPR) of silver nanoparticles. A phase shift as large as π is resolved in the resonance modes of the F-P microcavity due to the modulation by LSPR. This leads to complementary spectroscopic performance in the output of the plasmonic microcavity with respect to its non-plasmonic counterparts.

Surface plasmon effect of carbon nanodots

Luminescent ZnO quantum dots (QDs) have been prepared, and the fluorescence intensity of the QDs can be increased greatly with the introduction of carbon nanodots, while the fluorescence lifetime of the QDs decreases significantly. The fluorescence enhancement and lifetime decrement can be attributed to the surface plasmon effect of the carbon nanodots, and the calculated surface plasmon resonance frequency of the nanodots matches well with the fluorescence spectrum of the ZnO QDs.

Single Mode ZnO Whispering-Gallery Submicron Cavity and Graphene Improved Lasing Performance

Single-mode ultraviolet (UV) laser of ZnO is still in challenge so far, although it has been paid great attention along the past decades. In this work, single-mode lasing resonance was realized in a submicron-sized ZnO rod based on serially varying the dimension of the whispering-gallery mode (WGM) cavities. The lasing performance, such as the lasing quality factor (Q) and the lasing intensity, was remarkably improved by facilely covering monolayer graphene on the ZnO submicron-rod. The mode structure evolution from multimodes to single-mode was investigated systematically based on the total internal-wall reflection of the ZnO microcavities. Graphene-induced optical field confinement and lasing emission enhancement were revealed, indicating an energy coupling between graphene SP and ZnO exciton emission. This result demonstrated the response of graphene in the UV wavelength region and extended its potential applications besides many previous reports on the multifunctional graphene/semiconductor hybrid materials and devices in advanced electronics and optoelectronics areas.

Plasmon coupled Fabry-Perot lasing enhancement in graphene/ZnO hybrid microcavity

The response of graphene surface plasmon (SP) in the ultraviolet (UV) region and the realization of short-wavelength semiconductor lasers not only are two hot research areas of great academic and practical significance, but also are two important issues lacked of good understanding. In this work, a hybrid Fabry-Perot (F-P) microcavity, comprising of monolayer graphene covered ZnO microbelt, was constructed to investigate the fundamental physics of graphene SP and the functional extension of ZnO UV lasing. Through the coupling between graphene SP modes and conventional optical microcavity modes of ZnO, improved F-P lasing performance was realized, including the lowered lasing threshold, the improved lasing quality and the remarkably enhanced lasing intensity. The underlying mechanism of the improved lasing performance was proposed based on theoretical simulation and experimental characterization. The results are helpful to design new types of optic and photoelectronic devices based on SP coupling in graphene/semiconductor hybrid structures.

Electrically driven plasmon mediated energy transfer between ZnO microwires and Au nanoparticles

Electrically driven energy transfer between the surface defect states of ZnO quadrilateral microwires (MWs) and localized surface plasmon polaritons has been realized by means of introducing Au nanoparticles (NPs). An electroluminescence device with green emission using ZnO quadrilateral MWs, was fabricated. Once the Au NPs are sputtered on the surfaces of the ZnO MWs, the electroluminescence of the ZnO MWs will shift from green to red. Meanwhile, dual emissions were observed by means of sputtering Au NPs on a single ZnO MW periodically. Due to the Au NPs, electrically driven plasmon mediated energy transfer can achieve the modulation of amplifying, or quenching the surface defect emission. The relevant dynamic process of the surface plasmon mode mediated energy transfer was investigated. This new energy transfer method potentially offers an approach of modification and recombination of the surface defect state excitations of wide bandgap semiconductor materials.

Graphene induced high-Q hybridized plasmonic whispering gallery mode microcavities

A novel hybridized plasmonic whispering gallery mode (WGM) microcavities composed of graphene monolayer coated ZnO microrod with hexagonal cross section were proposed that operates in the ultraviolet region. π and π + σ surface plasmon modes in graphene monolayer at 4.7 eV and 14.6 eV can be used to achieve the near field coupling interaction between surface plasmonic modes and the conventional WGM microcavity modes in the ultraviolet band. Significantly, the coupling, happened in the evanescent wave field excited along the interface between ZnO and graphene, can lead to distinct optical field confinement and lasing enhancement experimentally, so as well as WGM lasing characteristics, such as the higher cavity quality factor (Q), narrower linewidth, lasing intensities enhancement. The results could provide a platform to study hybridized plasmonic cavity dynamics, and also provides the building blocks to construct graphene based novel microcavity for high performance ultraviolet laser devices with potential application to optical signal processing, biological monitoring, and so on.

Tunability of hybridized plasmonic waveguide mediated by surface plasmon polaritons

A hybridized plasmonic waveguide was proposed, which consisting of two kind of different metal films and a low-dielectric spacer layer inserted between. The spacer could be used to achieve the plasmonic resonance wavelength transfer from 450 nm to 600 nm, as well as the tunability of mode characteristics.