Enhancement Of Near Band Edge Emission Research Articles

Influence of Ni, Ti and NiTi alloy nanoparticles on hydrothermally grown ZnO nanowires for photoluminescence enhancement

In this work, surface-plasmon mediated enhanced photoluminescence emission has been investigated on Ni, Ti, and NiTi coated ZnO nanowires (NWs). ZnO NWs have been synthesized using a facile hydrothermal process, where NWs are coated with three different metals (Ni, Ti, and NiTi) using sputter deposition technique. It has been found that there is a significant improvement in near band edge emission (NBE) and passivation in deep level emission (DLE) in such metal embedded ZnO NWs and these emission properties can be tuned as we change the metal. Notably, we have achieved the highest enhancement of ∼6 times in NBE and best suppression of ∼15 times) in DLE by alloying of such metals (Ni and Ti). Such a remarkable DLE suppression is attributed to the presence of defect centers in ZnO NWs. The defect transition energy of ZnO is in resonance with the surface plasmon energy of metal nanoparticles, which leads to the conversion of DLE into NBE. The enhancement of NBE and suppression of DLE are possible due to the surface plasmon resonance coupling between metal nanoparticles (NPs) and ZnO NWs. Therefore, we conclude that earth abundant metals, such as Ni and Ti show significant SPR coupling on ZnO NWs and the alloying (NiTi) of such metals presents further improved SPR compared to the respective individual metals.

Tailoring UV emission from a regular array of ZnO nanotubes by the geometrical parameters of the array and Al2O3 coating

Self-aligned and equal-spaced zinc oxide (ZnO) nanotube arrays were fabricated with anodic aluminum oxide (AAO)-assisted growth and the ALD technique. The near band-edge (NBE) emission was strongly affected by the nanotube's geometrical parameters, such as a packing density and thickness of the nanotube walls. The NBE emission was further enhanced with Al2O3 coating. The effect was analyzed by X-ray photoelectron spectroscopy (XPS) and ascribed to the surface defect passivation and a ZnAl2O4 spinel formation. The NBE emission enhancement was greater in ZnO nanotubes with thicker walls. A smaller UV enhancement factor was explained by less uniform and integral Al2O3 coverage of the ZnO nanotubes with thinner walls; this, possibly induced a variation of the Al2O3 refractive index along the nanotubes. As a result, the optical conditions at the ZnO/Al2O3/air interfaces was changed and the light extraction efficiency was reduced in the latter samples.

Surface Plasmon Resonance-Enhanced Luminescence in Pd-Functionalized ZnO Nanowires.

Palladium (Pd)-functionalized ZnO nanowires were synthesized by thermal evaporation of a ZnO/graphite powder mixture followed by solution method. The ZnO nanowires had a rod-like morphology with relatively uniform width and length. The widths and lengths of the nanowires ranged from 30 to 100 nm and 5-10 µm, respectively. The diameters of the Pd particles on the nanowires ranged from 5 to 50 nm. Effects of postannealing on the photoluminescence properties of Pd-functionalized ZnO nanowires were examined. Thermal annealing resulted in an increase and decrease in the near-band edge (NBE) and deep level (DL) emission intensities of Pd-capped ZnO nanowires, respectively, whereas both the NBE and DL emission intensities of uncapped ZnO nanowires were increased by annealing. The intensity ratio of NBE emission to DL emission of the Pd-capped ZnO nanowires was increased ~18 fold by annealing in a hydrogen atmosphere. The underlying mechanism for NBE emission enhancement and DL emission suppression of Pd-capped ZnO nanorwires by postannealing is discussed based on the surface plasmon resonance effect of Pd.

Enhanced photoluminescence of nonpolar p-type ZnO film by surface plasmon resonance and electron transfer.

Nonpolar oriented Na-doped ZnO films were grown on m-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The films show repeatable p-type conductivity with a hole concentration of about 3.0×10(16) cm(-3) as identified by the Hall-effect measurements. 10-fold enhancement in the near-band-edge (NBE) emission of the nonpolar p-type ZnO by employing Pt nanoparticle surface plasmons has been observed. In addition, the deep level emission has been entirely suppressed. The underlying mechanism behind the enhancement of NBE emission and the quenching of defect emission is a combination of the electron transfer and the resonant coupling between NBE emission and Pt nanoparticle surface plasmons.

Enhanced near-band edge emission from ZnO nanorods by V2Os coating and subsequent thermal annealing.

V2O5-coated ZnO 1D nanostructures were prepared by using a two step process: thermal evaporation of a mixture of ZnO and graphite powders (ZnO:C = 1:1) in an oxidative atmosphere and sputter-deposition of V2O5. Scanning electron microscopy revealed that the nanostructures had a rod-like morphology with the thickness diminishing gradually from an end to the other. The thicknesses and lengths of the nanorods range from a few tens to a few hundreds of nanometers and from a few to a few tens of micrometers, respectively. Transmission electron microscopy and X-ray diffraction analyses revealed that the ZnO cores and V2O5 shells of the core-shell nanorods were wurtzite-type hexagonal close-packed structured single crystal and amorphous, respectively. The intensity ratio of the near-band edge (NBE) emission to the deep-level emission was increased about three times by coating the ZnO nanorods with a V2o5 thin film about 10 nm thick. The NBE emission enhancement may be mainly attributed to two sources: the effects of suppression of capturing of carriers by surface states and suppression of visible emission and nonradiative recombination by depletion regions formed in the ZnO cores. In addition, it was found that postannealing of V2O5-coated ZnO nanorods is not desirable, whereas post annealing makes a positive effect on the NBE emission enhancement in uncoated ZnO nanorods.

Tunable enhancement of exciton emission from MgZnO by hybridized quadrupole plasmons in Ag nanoparticle aggregation

Mg0.2Zn0.8O/metal nanoparticle systems have been fabricated and investigated. The photoluminescence results indicate that Al and Au nanoparticles could slightly enhance the near-band-edge (NBE) emission from Mg0.2Zn0.8O. In contrast, a giant and tunable NBE emission enhancement could be induced by Ag nanoparticles based on the coupling interaction between the hybridized quadrupole plasmon in Ag nanoparticle aggregation and the excitons of Mg0.2Zn0.8O. Interestingly, the intensity and position of the narrow quadrupole resonance could be controlled by tuning the interspace gap and size of Ag nanoparticles, which was clearly demonstrated both experimentally and theoretically. Our findings may pave the way for further development of high-efficiency UV light-emitting devices.

Enhanced photoluminescence of Au-functionalized ZnO nanorods annealed in a hydrogen atmosphere

Au-functionalized ZnO nanorods were synthesized by carbothermal evaporation of a mixture of ZnO and graphite powders at 900°C followed by gold (Au) sputter-deposition and thermal annealing. The ZnO nanorods had a rod-like morphology with relatively uniform width and length. The widths and lengths of the nanorods ranged from 50 to 100nm and 3–4μm, respectively. The diameters of the Au particles on the nanorods ranged from 5 to 40nm. The dependence of the photoluminescent properties of Au-functionalized ZnO nanorods on the postannealing atmosphere was examined. Annealing resulted in an increase and decrease in the near-band edge (NBE) and deep level (DL) emission intensities of Au-coated ZnO nanorods, respectively, whereas both the NBE and DL emission intensities of uncoated ZnO nanorods were increased by annealing. The intensity ratio of NBE emission to DL emission of the Au-capped ZnO nanorods was increased ~25 fold by hydrogen annealing. The underlying mechanism for NBE emission enhancement and DL emission suppression of Au-capped ZnO nanorods by postannealing is discussed based on the surface plasmon resonance effect of Au.

Enhanced luminescence of Ag-decorated ZnO nanorods

Ag-decorated ZnO nanorods were synthesized by thermal evaporation of a mixture of ZnO and graphite powders at 900 °C followed by wet Ag coating and thermal annealing. The ZnO nanorods had a rod-like morphology with a relatively uniform width and length. The widths and lengths of the nanorods ranged from 50 to 300 nm and up to a few hundred micrometers, respectively. The diameters of the Ag particles on the nanorods ranged from 10 to 100 nm. The dependence of the photoluminescence properties of Ag-decorated ZnO nanorods on the postannealing atmosphere was examined. Annealing resulted in an increase and decrease in the near band edge (NBE) and deep level (DL) emission intensities of Ag-coated ZnO nanorods, respectively, whereas both the NBE and DL emission intensities of uncoated ZnO nanorods were increased by annealing. The intensity ratio of NBE emission to DL emission of the Ag-coated ZnO nanorods was increased ~15-fold by hydrogen annealing. The underlying mechanism for NBE emission enhancement and DL emission suppression of Ag-coated ZnO nanorods by postannealing is discussed based on the surface plasmon resonance effect of Ag.

Great enhancement of near band-edge emission of ZnSe two-dimensional complex nanostructures fabricated by the interference of three femtosecond laser beams

By using the method of the interference of three 800 nm femtosecond laser beams, we fabricated complex 2-dimensional (2D) micro/nanostructures on ZnSe crystal. Compared with the plane surface of ZnSe crystal, 2D nanostructures exhibit a great enhancement of near band-edge (NBE) emission and a compression of second harmonic generation (SHG) under excitation of infrared (IR) femtosecond laser with central wavelengths ranging from 1200 to 1600 nm. We studied the photoluminescence properties of 2D nanostructures and the mechanism of the enhancement of NBE emission. Our results indicated that the enhancement of NBE emission is caused by a combination of several processes including the increase in optical absorption, and the reabsorption of SHG by the nanostructures.

Enhancement of near-band edge emission of Au/ZnO composite nanobelts by surface plasmon resonance

In this paper, ZnO nanobelts were synthesized by chemical vapor deposition. And then Au nanoparticles were sputtered on the ZnO nanobelts. Enhancement of the near-band edge emission of Au/ZnO composite nanobelts was observed from photoluminescence measurement due to the coupling between the defect emission from ZnO and surface plasmons of Au nanoparticles, compared to bare ZnO nanobelts. The coupled energy could be transferred into free space photons when the interface is sufficiently rough to scatter the surface plasmons. The enhancement ratio of the near-band edge emission of Au/ZnO is 11-fold higher than that of bare ZnO. The enhancement mechanism was proposed based on scattering and absorption by Au nanoparticles.