Enhancement Of Band Edge Emission Research Articles

Resonance plasmonic coupling: selective enhancement of band edge emission over trap state emission of CdSe quantum dots.

The photoluminescence properties of quantum dots (QDs) are often enhanced by eliminating surface trap states through chemical methods. Alternatively, a physical approach is presented here for improving photoluminescence purity in QDs by employing frequency-specific plasmon resonance coupling. Emitter-bound plasmonic hybrids are designed by electrostatically binding negatively charged QDs in water to positively charged gold nanoparticles having a thin polymer coating. Herein, two types of QDs are used: (i) bare CdSe, which exhibits both band edge and trap state emission, and (ii) CdSe overcoated with a ZnS shell (CdSe/ZnS) devoid of trap state emission. Tuning the extinction spectrum of the plasmonic system to match the band edge emission of CdSe enables the selective enhancement of band edge emission over trap state emission. Excellent match in the extinction spectrum of the gold nanoparticle with both, experimentally calculated photoluminescence enhancement factor and theoretically calculated radiative rate enhancement signifies the role of frequency-specific plasmon resonance coupling. Plasmon-coupled photoluminescence of CdSe/ZnS is further investigated by varying the number density of emitter on the surface of plasmonic nanoparticle. An enhancement in the photoluminescence is observed at a lower emitter density of CdSe/ZnS and the photoluminescence enhancement factor closely follows the plasmon resonance. However, photoluminescence quenching occurs with an increase in CdSe/ZnS due to plasmon-assisted nonradiative energy transfer between nearby QDs, as indicated by a red shift in the PL maximum. These studies establish that resonance plasmonic coupling is a convenient physical strategy for tuning the intrinsic photoluminescence properties of QDs for various optoelectronic applications.

One-pot synthesis of Ag-In-Ga-S nanocrystals embedded in a Ga2O3 matrix and enhancement of band-edge emission by Na+ doping.

I-III-VI-based semiconductor quantum dots (QDs) have been intensively explored because of their unique controllable optoelectronic properties. Here we report one-pot synthesis of Na-doped Ag-In-Ga-S (AIGS) QDs incorporated in a Ga2O3 matrix. The obtained QDs showed a sharp band-edge photoluminescence peak at 557 nm without a broad-defect site emission. The PL quantum yield (QY) of such QDs was 58%, being much higher than that of AIGS QDs without Na+ doping, 29%. The obtained Na-doped AIGS/Ga2O3 composite particles were used as an emitting layer of green QD light-emitted diodes. A sharp electroluminescence (EL) peak was observed at 563 nm, being similar to that in the PL spectrum of the QDs used. The external quantum efficiency of the device was 0.6%.

Publisher’s Note: “Band-edge emission enhancement in sputtered ZnO thin films with ultraviolet surface lattice resonances” [J. Appl. Phys. 130, 223103 (2021)

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Band-edge emission enhancement in sputtered ZnO thin films with ultraviolet surface lattice resonances

Metallic nanostructures acting as optical nanoantennas can significantly enhance the photoluminescence (PL) of nearby emitters. Albeit luminescence enhancement factors of several orders of magnitude have been reported for quantum dots or molecules, in the case of bulk emitters, the magnitude of the plasmonic enhancement is strongly hindered by the weak spatial overlap between the active medium and the electromagnetic modes of the nanoantenna. Here, we propose a solid-state ultraviolet emitter based on a thin film of zinc oxide (ZnO) coupled with an array of aluminum (Al) nanoparticles. The Al nanorod array is designed to sustain surface lattice resonances (SLRs) in the near ultraviolet, which are hybrid modes exhibiting a Fano-like lineshape with narrowed linewidth relatively to the non-hybridized plasmonic modes. By changing both the period of the array and the dimensions of the nanorods, the generated SLR is tuned either to the near band-edge (NBE) emission of ZnO or to the excitation wavelength. We experimentally demonstrate that NBE emission can be increased up to a factor of 3 compared to bare ZnO. The underlying PL enhancement mechanisms are experimentally investigated and compared with numerical simulations. We also demonstrate that SLRs are more efficient for the ZnO luminescence enhancement compared to localized surface plasmon resonances.

Largely enhanced near band edge emission of ultrathin zinc oxide nanowire/gold nanoparticles composites by surface plasmon resonance

Ultrathin zinc oxide nanowires with diameter less than 50nm were synthesized by polyethyleneimine assisted solution method. Zinc oxide nanowire near band edge emission was enhanced obviously by gold nanoparticles coating, and a max 26 times enhancement was realized. The defects caused visible light emission was also quenched to noise level when gold was deposited more than 10s. The large near band edge emission enhancement was caused by surface plasmon resonance mediated luminescent energy transfer, which absorbed the visible light energy and transferred to the near band edge emission. The large surface to volume ratio enhanced the coupling strength between gold nanoparticles and ultrathin zinc oxide nanowires. This research provide a method to improve the luminescent efficiency of zinc oxide nanowires.

Spectroscopic and Photoluminescent Properties of Indium Zinc Oxide (IZO) and IZO/Ag/IZO Sandwiched Film

We report the ellipsometric and photoluminescence (PL) properties of Indium zinc oxide (IZO) films, which were grown by radio frequency sputtering under Ar and O2 atmospheres. IZO films grown under an O2 atmosphere (IZO (O2)) showed enhanced PL properties when compared to the films grown under an Ar atmosphere (IZO (Ar)), particularly with respect to the band-edge emission. The enhancement of band-edge emission can be attributed to the reduction in the non-emissive defect states related to oxygen vacancies, which were repaired by sputtering under O2 atmosphere, whereas the PL enhancement in green region is probably due to the formation of the different types of defects under the excess oxygen environment. This was also supported by the results of time-resolved PL measurements, where the band-edge emission of IZO (Ar) showed rapid decay with a 50 ps lifetime, which indicates the dominance of the relaxation pathway to underlying defect states. In contrast, the PL decay profiles of IZO (O2) for band-edge and emissive defect states showed moderate decay with time-constants of 2.3 ns and 5.7 ns, respectively. The exciton relaxation dynamics were sensitive to the presence and its kinds of defect states, which were controlled by the growth conditions.

Evidence of Silicon Band-Edge Emission Enhancement When Interfaced with SiO2:Er Films

Nearly two-orders of magnitude increase in room-temperature band-to-band (1.067 eV) infrared emission from crystalline silicon, coated with erbium-doped sol–gel films, have been achieved. Phonon-assisted band-to-band emission from coated and annealed p-Si is strongest for the sample annealed at 700°C. In this paper, evidence of the origin of the emission band from the band edge recombination activities is established. Enhancement of radiative recombination of free carriers is reasoned by stresses at the interface due to the annealed sol–gel-deposited silica. Comparative studies with other strained silicon samples are presented.

Enhanced photoluminescence of ZnO nanorods via coupling with localized surface plasmon of Au nanoparticles

We demonstrated the synthesis of ZnO nanorods by using a facile solution route at low temperature. Au nanoparticles were deposited on the surface of ZnO nanorods by an in-situ solution method. The ZnO nanostructures had nanorod-like morphology in large quantity and possessed high crystallinity. An enhancement of ultraviolet emission of ZnO nanorods was observed as a result of Au nanoparticles decoration, while green emission was suppressed. This excellent photoluminescence performance is attributed to surface-plasmon-mediated quenching of defect emission and the enhancement of band-edge emission. The defect transition energy (green) of ZnO nanorods is in resonance with the localized surface plasmon energy of the Au nanoparticles, which led to the conversion of deep level green emission into band-edge ultraviolet emission.

Surface-plasmon-mediated red and near infrared emission from Au-coated ZnO/ZnCr2O4 nanocomposites

The room-temperature photoluminescence spectra of Au coated hydrothermally grown ZnO nanorods were investigated. Au coated ZnO nanorods were found to exhibit very large near band edge emission enhancement. Further by controlling the concentration of K2Cr2O7 in the precursor solution, the composition of the products has been significantly changed from ZnO nanorods to ZnO/ZnCr2O4 nanocomposites. Interestingly, the Au coating on ZnO/ZnCr2O4 nanocomposites has shown enhanced red and NIR emission and almost suppressed UV emission. A plausible mechanism has been proposed for the enhancement in red emission. The work presented here has tremendous potential for ZnO based red luminescent devices.

Light emission enhancement based on surface plasmon resonance in zinc oxide/silver film on digital video disk template

ABSTRACTThe photoluminescence signals of zinc oxide/silver films based on digital video disk template were carried out compared with that of the planar mode. The spectra that on silicon showed a strong bandgap emission around 378 nm and a defect related emission band centered at ∼470 nm. After adding digital video disk template, it resulted in an increased signal of both the ultraviolet and the visible region, but the ultraviolet emission enhancement was notable. That the enhancement of band edge emission resulted from surface plasmon resonance coupling between silver and zinc oxide was discussed in detail.

Selective tuning of enhancement in near band edge emission in hydrothermally grown ZnO nanorods coated with gold

The room-temperature photoluminescence (PL) spectra of hydrothermally grown ZnO nanorods (NRs) coated with Au using dc sputtering and thermal evaporation were systematically investigated. Au coated (via dc sputtering) ZnO NRs were found to exhibit very large near band edge emission enhancement, on the contrary Au coated (via thermal evaporation) ZnO NRs showed suppression in the near band edge emission peak. These observed results were further confirmed by excitation intensity (EI) dependent PL spectra of different samples. Further using Raman spectra it has been observed that the longitudinal optical (LO) phonons exhibit an enhancement and a weakening by the Au coatings, using dc sputtering and thermal evaporation respectively. Finally by controlling the concentration of KMnO4 as an additive during the hydrothermal growth, selective tuning in the defect density was carried out, which was later utilized to probe the effect of defect density of the Au–ZnO plasmonic coupling. Moreover, our results strongly suggest that the EI dependent PL has a strong dependence on the metal coating technique. The findings presented in this article clearly indicate the dependence of Au–ZnO plasmonic coupling on the overall defect density and the process of Au deposition.

Surface state and optical property of sulfur passivated InP

We report photoluminescence (PL) of indium phosphide (InP) surface passivated by sulfur (S). A three-fold enhancement of band edge emission from the bulk InP was observed after the InP was passivated by ammonium sulfide ((NH4)2S) solution for 10min. X-ray photoelectron spectroscopy measurements indicate that the oxide at InP surface is removed after being sulfurized in (NH4)2S solution. However, the enhancement significantly decreases for a longer treatment time, which is maybe due to a thick S layer deposited at the InP surface resulting in low light transmission.

Band edge emission enhancement by quadrupole surface plasmon–exciton coupling using direct-contact Ag/ZnO nanospheres

Periodic Ag nanoball (NB) arrays on ZnO hollow nanosphere (HNS) supporting structures were fabricated in a large area by a laser irradiation method. The optimized laser power and spherical supporting structure of ZnO with a certain size and separation were employed to aggregate a sputtering-deposited Ag nano-film into an ordered, large-area, and two dimensional Ag NB array. A significant band edge (BE) emission enhancement of ZnO HNSs was achieved on this Ag NB/ZnO HNS hybrid structure and the mechanism was revealed by further experimental and theoretical analyses. With successfully fabricating the direct-contact structure of a Ag NB on the top of each ZnO HNS, the highly localized quadrupole mode surface plasmon resonance (SPR), realized on the metal NBs in the ultraviolet region, can effectively improve the BE emission of ZnO through strong coupling with the excitons of ZnO. Compared with the dipole mode SPR, the quadrupole mode SPR is insensitive to the metal nanoparticle's size and has a resonance frequency in the BE region of the wide band gap materials, hence, it can be potentially applied in related optoelectronic devices.

Ultra-thin conformal deposition of CuInS2 on ZnO nanowires by chemical spray pyrolysis

CuInS2 (CIS) was deposited on ZnO nanowires by a chemical spray pyrolysis (CSP) method, resulting in an ultra-thin, conformal CIS coating on ZnO forming ZnO–CIS core–shell structures. A high-resolution transmission electron microscope and elemental mapping showed the excellent quality of the coating, while Raman spectroscopy revealed the purity of the materials after core–shell formation. A significant enhancement in band-edge emission of ZnO after CIS coating (also lower defect emissions) was observed, which is due to the peculiar band alignment of the ZnO–CIS combination. Further, the electrical behaviour of the single nanowire ZnO–CIS diode was studied, demonstrating the excellent interface between CIS and ZnO. This technique provides tremendous potential for the fabrication of low-cost nano-electronic devices.

Physical approaches to tuning the luminescence color patterns of colloidal quantum dots

Localized surface plasmon resonance (LSPR) and photoactivation (PA) effects are combined for the tuning of fluorescent colors of colloidal CdSe quantum dots (QDs). It is found that LSPR with QD emitters intensely enhances surface state emission, accompanied by a remarkable red-shift of fluorescent colors, while PA treatment with colloidal QDs leads to a distinct enhancement of band-edge emission, accompanied by a peak blue-shift. Furthermore, the LSPR effect on QD emitters can be continuously tuned by the PA process. The combination of the post-synthetic approaches allows feasible realization of multi-color patterns from one batch of QDs and the approaches can also be compatible with other micro-fabrication technologies of QD embossed fluorescent patterns, which undoubtedly provides a way of precisely tuning the colors of light-emitting materials and devices that use colloidal QDs.

Surface plasmon enhanced bandgap emission of electrochemically grown ZnO nanorods using Au nanoparticles

Electrochemical deposition of ZnO nanorods having a diameter of 80–150nm and length ~2μm has been carried out. Au particles were sputtered on the ZnO nanorods for different sputtering times (from 0 to 100s). The Photoluminescence spectra of bare ZnO nanorods showed a weak bandgap emission at around 375nm and a broad defect-related emission band centered at ~596nm. After the Au sputtering, the defect-related emission disappeared for all the samples. Moreover, the band edge emission intensity was enhanced with Au sputtering time 50s. The enhancement factor reached a maximum value for the Au sputtering time of 50s The enhancement in band edge emission is due to the transfer of electrons from defect states to the Au nanoparticles that cause not only an increase of resonant electron density, but also creates energetic electrons in the higher energy states. These resonant electrons can escape from the surface of the Au nanoparticles to conduction band of ZnO nanorods leading to the suppression of defect related emission intensity.

Enhancement of band-edge emission of ZnO from one-dimensional ZnO/MgZnO core/shell nanostructures

One-dimensional MgZnO nanostructures were grown directly on p-Si substrates by thermal evaporation at a variety of synthesis temperatures. Transmission electron microscopy and energy dispersive x-ray spectroscopy analysis revealed the formation of slim ZnO nanowires with twin boundaries on low Mg content nanosheets at lower synthesis temperatures, where the slim nanowires on the nanosheet did not have any detectable Mg content. The MgZnO nanostructures at elevated synthesis temperatures showed core/shell structures consisting of h-ZnO/h-MgZnO/c-MgZnO, where the h-MgZnO layer has a Mg content up to ∼9 at% and a further increase in Mg content in the outer shell induced the formation of the c-MgZnO phase. The ZnO nanorods covered with MgZnO layers showed enhanced band-edge emission due to the existence of a h-MgZnO barrier and a c-MgZnO dielectric layer.

Band-edge emission enhancement by longitudinal stress field in GaN

Bright ultraviolet luminescence in the wing region of epitaxial-lateral-overgrowth GaN was studied by cathodoluminescence. Analysis of dislocation bending and movement by transmission electron microscopy demonstrates the emergence of another longitudinal stress field, which effectively enhances the band-edge light emission. Ab initio calculations of interband transition probability provide a model showing that introduction of appropriate additional stress component in the longitudinal direction of GaN will improve the efficiency of band-edge emission.

Optical properties of a ‐plane GaN strained by photo‐chemically grown gallium hydroxide

AbstractWe report the observation of green emission centered at 500nm, accompanied with luminescence enhancement and spectral blue shift (∼31meV) in the bandedge emission from a ‐plane grown gallium nitride (GaN) passivated with gallium hydroxide (GaOOH). From study of the photo‐current response and polarization‐resolved low‐temperature micro‐photoluminescence (μ ‐PL) we resolved an evolution of gain competition process between the green and the UV emission bands. By dissolving the oxide we recover the emission characteristics of the as‐grown a ‐GaN. These observations can be ascribed to a formation of compressively‐strained a ‐GaN due to a coherently grown GaOOH atop layer. The latter is responsible for the spectral blue shift and the generation of acceptor like deep‐levels causing the green‐band transition in the emission and photo‐current response. Enhancement of bandedge emission from the oxide covered a ‐GaN is due to the GaOOH surface passivation effect which was prepared by the photo‐enhance wet oxidation method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhancement of band-edge emission induced by defect transition in the composite of ZnO nanorods and CdSe/ZnS quantum dots

A new and general approach to enhance band-edge emission at the expense of defect emission in a semiconductor nanocomposite is proposed. The underlying mechanism is based on the resonance effect between defect transition and band-to-band excitation and transfer of excited electrons between conduction band edges. With our approach, it is possible to convert defect loss into bandgap emission. As an example, we demonstrate that the bandgap emission of ZnO nanorods can be enhanced by as much as 30 times when they are compounded with CdSe/ZnS nanoparticles.