Photoluminescence Properties Of ZnO Nanowires Research Articles

Mechanism of photoluminescence quenching in visible and ultraviolet emissions of ZnO nanowires decorated with gold nanoparticles

Decorating with metal nanoparticles (NPs) is an effective way to tune the photoluminescence (PL) properties of ZnO nanowires (NWs), but the mechanism for this is insufficiently understood. In this study, ZnO NWs with lower work function were synthesized on Si substrates using thermal oxidation. Au NPs were incorporated onto the surface of the ZnO NWs. The PL properties of ZnO NWs decorated with Au NPs of different sizes were systematically investigated. Quenching rather than enhancement of both the near-band-edge and visible emission of ZnO NWs was observed after decoration with Au NPs. Introducing an approximately 2-nm-thick Al2O3 insulating layer between the ZnO NWs and Au NPs caused the quenching phenomenon to disappear. These results suggest that the quenching was caused by electron transfer from ZnO to the Au NPs under UV irradiation and the PL properties of ZnO NWs decorated with Au NPs are also related to the band structure of ZnO.

Raman and photoluminescence properties of ZnO nanowires grown by a catalyst‐free vapor‐transport process using ZnO nanoparticle seeds

We report the synthesis of ZnO nanowires by a catalyst‐free vapor‐transport process on SiO2/Si substrates. A modification of the method was performed using small ZnO nanoparticles (∼5 nm) in low concentration suspensions. The use of dichloromethane or toluene in the suspensions influences the nanoparticle distribution over the surface. The obtained nanowires have diameters ranging from 20 to 100 nm and lengths from 0.5 to 1 µm. Raman scattering results show a narrow (∼7 cm−1) full width at half maximum of the E2high optical phonon mode, which demonstrate a good‐crystal quality of the ZnO nanowires obtained. Room temperature photoluminescence measurements show a broad emission band in the visible range at 430–830 nm, which is attributed to intrinsic defects. A notable decrease of this visible band was achieved making this method suitable for almost defect‐free ZnO nanowires. The photoluminescence results at 5 K demonstrate the role of surface defects as responsible for the visible band.

Effect of Growth Conditions on Morphology and Photoluminescence Properties of ZnO Nanowires Fabricated by Thermal Evaporation without a Metal Catalyst

We demonstrate that single crystalline ZnO nanowires with large length/diameter ratio are successfully grown on Si, glass, and Si with ZnO seed layer via simple thermal vapor deposition, without introducing any catalyst or additive. In this work, we study impact of growth conditions such as growth temperature, substrates, and ZnO seed layer on morphology and photoluminescence properties of ZnO nanowires, in terms of systematic characterizations. The investigations show that the growth temperatures have substantial effect on the morphology of ZnO nanowires, while substrates have low impact. And 700 °C is believed to be the optimized growth temperature among the series of temperatures. Moreover, ZnO seed layer plays an important role in the uniformity and reproducibility of ZnO nanowires growth. PL measurements for the ZnO nanowires exhibit two emission bands including a UV emission and a blue emission, respectively. Finally, the growth behavior of the ZnO nanowires is discussed based on the VS growth mechanism. Our resluts have made a positive progress toward improving control of the morphology of ZnO nanowires.

Crystal phase engineered quantum wells in ZnO nanowires

We report the fabrication of quantum wells in ZnO nanowires (NWs) by a crystal phase engineering approach. Basal plane stacking faults (BSFs) in the wurtzite structure can be considered as a minimal segment of zinc blende. Due to the existing band offsets at the wurtzite (WZ)/zinc blende (ZB) material interface, incorporation of a high density of BSFs into ZnO NWs results in type II band alignment. Thus, the BSF structure acts as a quantum well for electrons and a potential barrier for holes in the valence band. We have studied the photoluminescence properties of ZnO NWs containing high concentrations of BSFs in comparison to high-quality ZnO NWs of pure wurtzite structure. It is revealed that BSFs form quantum wells in WZ ZnO nanowires, providing an additional luminescence peak at 3.329 eV at 4 K. The luminescence mechanism is explained as an indirect exciton transition due to the recombination of electrons in the QW conduction band with holes localized near the BSF. The binding energy of electrons is found to be around 100 meV, while the excitons are localized with the binding energy of holes of ∼5 meV, due to the coupling of BSFs, which form QW-like structures.

Growth behavior and photoluminescence properties of ZnO nanowires on gold nano-particle coated Si surfaces

ZnO nanowires arrays were synthesized on gold coated Si by the hydrothermal technique. The density of the ZnO nanowires array is found to be inversely proportional to the particle size of gold films. The initial nucleation of ZnO nanowires is found to nucleate at the boundaries of the gold nano-particle films. The density of the ZnO nanowires can be controlled through the particle size of the gold nano-particle films. Anomalous photoluminescence properties were observed from the as-grown ZnO nanowires.

Enhancement of the near-band-edge photoluminescence of ZnO nanowires: Important role of hydrogen incorporation versus plasmon resonances

We investigated the photoluminescence properties of ZnO nanowires coated with Au, Ag, and Pt nanoparticles deposited by dc sputtering. A strong enhancement of the near-band-edge emission was observed in all metal-coated samples but also if the samples were treated with Ar plasma without any nanoparticle deposition. High-resolution photoluminescence spectroscopy revealed hydrogen-donor-bound-exciton emission in all samples indicating unintentional hydrogen incorporation. A shorter decay time of the near-band-edge emission was observed in all cases. The results indicate that unintentional hydrogen incorporation plays a dominant role when metal deposition is performed by sputtering.

Determination of the microstructure of Eu-treated ZnO nanowires by x-ray absorption

X-ray absorption near-edge structure (XANES), extended x-ray absorption fine structures (EXAFS), and photoluminescence measurements were used to elucidate the microstructural and photoluminescence properties of ZnO nanowires (ZnO-NWs) that had been treated with Eu by thermal diffusion. The O K- and Eu L3-edge XANES and EXAFS spectra at the Zn K- and Eu L3-edge verified the formation of Eu2O3-like layer on the surface of ZnO-NWs. X-ray diffraction, XANES and EXAFS measurements consistently suggest the lack of substitutional doping of Eu ions at the Zn ion sites in the interior of ZnO-NWs. The clear sharp and intense emission bands in the range 610–630 nm of Eu-treated ZnO-NWs originated from the intra-4f transition of Eu ions in the Eu2O3-like surface layer.

Stable enhancement of near-band-edge emission of ZnO nanowires by hydrogenincorporation

We report on the photoluminescence properties of ZnO nanowires treated with a mild Arplasma. The nanowires exhibited stable and strong enhancement of the near-band-edgeemission and quenching of the deep level emission. The low temperature PL revealed astrong hydrogen donor–bound-exciton line in the plasma-treated samples indicatingunintentional incorporation of hydrogen during the plasma treatment. To confirm theresults, hydrogen was implanted into the ZnO nanowires with a low ion energy of 600 eVand different fluences. The observed result can be related to the passivation of deep centersby hydrogen. The absolute photoluminescence intensity measured by an integrating sphereshowed stable and strong UV emission from the treated samples even after several weeks.

Influence of metallic coatings on the photoluminescence properties of ZnO nanowires

AbstractWe report on low‐temperature photoluminescence studies of ZnO nanowires coated with thin metallic films. For all analyzed metals (Al, In, Au, Ni, Cu), we find an increased relative intensity of the green deep‐level emission. This is accompanied by a significant reduction of the relative intensity of the surface exciton band. The observed effects are most likely related to the formation of metal induced gap states in the surface region of the ZnO nanowires. A model for the band structure in the surface region of the metal‐coated nanowires is proposed that successfully explains the changes in the photoluminescence spectra after the coating process. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of low-energy hydrogen ion implantation on optical properties of ZnO nanowires

The low-energy hydrogen ions (2 keV; 1 × 10 15 to 1 × 10 18 cm −2 per dose) implantation was used to study the passivation effect of defects and photoluminescence properties of ZnO nanowires. The implanted H + effectively passivated deep level native defects, making the visible emission at 500 nm disappear completely and the UV emission (380 nm) of nanowires enhance for seven times. H + implantation at higher dose induced a strongly new violet emission broad peak (around 410 nm) which may originate from the hydrogen related complex of defects. However, this violet emission disappeared after annealing in argon atmosphere at 300 °C, confirming that the new violet emission is related to hydrogen. All emission peaks vanished due to the formation of a large quantity of nonradiative recombination centers at high dose implantation. This controllable method of hydrogen doping may find potential application in UV/violet optoelectronic and especially in nano-optoelectronic devices.

Influence of polymer coating on the low-temperature photoluminescence properties of ZnO nanowires

We report on low temperature photoluminescence studies of ZnO nanowires embedded in different polymers. Comparing the spectra of as-grown and embedded ZnO nanowires, we find a decrease of the deep-level emission and an increase of the near band-edge emission after the embedding process. The near band-edge emission of the embedded ZnO nanowires is dominated by a surface exciton band. The observed effects are independent of the selected polymer. The decrease of the deep-level emission scales with the balling abilities of the different polymers. We propose a model to explain the spectral changes.

Acceptor related photoluminescence from ZnO:Sb nanowires fabricated by chemical vapor deposition method

Single-crystal Sb doped ZnO nanowires were fabricated on Si (1 0 0) substrate by a chemical vapor deposition method. The photoluminescence properties of ZnO nanowires were studied with the temperature ranging from 81 to 306 K. At 81 K, the recombination of the acceptor-bound exciton was predominant in PL spectrum, which was attributed to the transition of the (Sb Zn–2V Zn) complex bound exciton. The activation of A 0X and the acceptor binding energy had been calculated to be 16.8 and 168 meV, respectively.

Synthesis and photoluminescence properties of ZnO nanowires and nanorods by thermal oxidation of Zn precursors

A newly developed route has been used to fabricate single-crystalline thin ZnO nanowires (T-ZNWs) and ZnO nanorods (ZNRs) by simple thermal oxidation of wirelike Zn precursors under 5 Pa at 400 °C and 600 °C, respectively. The T-ZNWs grow along the [21¯1¯0] direction via a “self-catalytic liquid–solid” process, while the ZNRs grow along the [0001] direction following a vapor–solid mechanism. Photoluminescence (PL) spectra were used to investigate the optical properties of the oxidized samples. The products consisting of the T-ZNWs and thick trunks show a strong green emission related to the oxygen vacancies, while the ZNRs oxidized at higher temperature exhibit strong ultraviolet emission with negligibly weak green emissions, indicating the high optical quality of ZNRs.

Hydrothermal synthesis and photoluminescence properties of ZnO nanowires

Hydrothermal synthesis and photoluminescence properties of ZnO nanowires

Hydrothermal synthesis and photoluminescence properties of ZnO nanowires

Single-crystalline ZnO nanowires were synthesized by a simple hydrothermal process. The as-synthesized ZnO nanowires have diameters of 50–80 nm and lengths of over 6 μm (the aspect ratios of ∼100). They show a strong UV emission at ∼392 nm using a Xe lamp as the excitation source at room temperature.