Photoluminescence Properties Of ZnO Research Articles

Insight of the role of F-impurity on the structural, electro-optical properties of ZnO: DFT and experiment

A comprehensive study is performed to investigate the consequence of F doping on the structural, electronic, optoelectrical, and photoluminescence properties of ZnO. In the theoretical part, the density functional theory (DFT) is used to study the electronic and optical properties of F-doped ZnO. Whereas, the role of F on the structural, morphological, and optoelectrical characteristics of spray deposited ZnO thin films are studied by experimental means. Electronic band structures, density of states, and optical properties indicated that F is an efficient donor and broadened the direct band gap of F:ZnO system because of the well-known Burstein-Moss effect which matches the experimental data. Shifting of the Fermi level into conduction band (CB) fallouts the improvement of electrical conductivity and carrier concentrations of the doped system. The lattice constants of ZnO are increased due to F doping which is in accord with our experimental results. The existence of F1s in the films is confirmed by X-ray photoelectron spectroscopy (XPS) inspection. Surface morphology reveals the formation of nano-wall structures with different aspect ratios. Photoluminescence spectra show PL emissions for un-doped and 5% F-doped samples at 3.38 eV assigned to the near band edge (NBE) emission and weak peaks at 2.74 and 2.63 eV are attributed to emission from defect states. The optical band gap value first decreased up to 1% F content and then started to increase with increasing F concentration, which is well supported by the theoretical results. The findings from this study will be helpful for further investigation and selecting suitable areas of applications.

Thermal Treatments and Photoluminescence Properties of ZnO and ZnO:Yb Films Grown by Magnetron Sputtering

This work is on ZnO and ZnO:Yb (0.3 at%) films prepared on (100) Si substrates by magnetron sputtering and deals with their structural and photoluminescence evolutions upon annealing at different temperatures from 873 to 1173 K during 1 h under N2 atmosphere. The microstructural characterizations reveal that, for both sample series, annealing treatment improves the crystallinity of ZnO of the upper part of the films. However, (002) textured ZnO columnar growth is only observed for ZnO films. For annealing temperatures higher than 973 K, rare earth and Si diffusions toward the film/substrate interface are observed resulting in the appearance of a zinc silicate phase for ZnO films and a composite material made of nanoscale ZnO grains surrounded by an amorphous phase for ZnO:Yb films. In addition, photoluminescence measurements show that Yb doping in ZnO results in a lower integrated photoluminescence intensity compared to that of ZnO films and the photoluminescence response in the visible spectral range is also modified most probably due to the presence of dopant. Furthermore, the PL intensity at 980 nm originating from electronic transitions between 2F5/2 and 2F7/2 levels of Yb3+ ion increased with temperature. At last, the evolutions of the PL emissions with temperature from the ZnO defects are discussed.

Photoluminescence Properties of ZnO Micro/Nanostructures Capped with Various Surfactants

Photoluminescence Properties of ZnO Micro/Nanostructures Capped with Various Surfactants

Photochemical Synthesis of Hierarchical Multiple-Growth-Hillock Superstructures of Silver Nanoparticles on ZnO

Hierarchical superstructures of Ag nanoparticles with novel morphology resembling multiple growth hillocks were synthesized for the first time using photochemical method through the screw-dislocation-driven, nanoparticle-mediated crystal growth mechanism. The Ag nanoparticles were in situ synthesized from the photoreduction of Ag+ ions adsorbed on ZnO. The absence of organic capping agents in the synthesis protocol makes this photochemical approach suitable for preparing metal/semiconductor hybrid materials with clean metal/semiconductor interfaces that can find important applications in plasmon-assisted photocatalysis, photovoltaics, and plasmon-enhanced spectroscopies. Finally, we demonstrated that the photoluminescence properties of ZnO can be subtly modified by the photodeposited Ag nanostructures through synergistic mechanisms of surface plasmon–exciton resonant coupling and surface passivation.

The effects of Al doping and post-annealing via intrinsic defects on photoluminescence properties of ZnO:Eu nanosheets

Europium (Eu) and Aluminum (Al) co-doped ZnO nanosheets were synthesized by a hydrothermal method. The effects of Al concentration as a dopant and post-annealing of ZnO:Eu nanosheets on its structural, electrical and optical properties were investigated in detail. Prepared samples were characterized structurally using X-ray diffraction (XRD), morphologically using scanning electron microscopy (SEM) and optically using photoluminescence (PL) spectroscopy analyses. No diffraction peak related to dopants in XRD spectrum along with shift in peaks angles relevant to ZnO proved that Al and Eu ions were doped successfully into ZnO nanosheets. This study recommends that extrinsic doping and intrinsic defects have impressive roles on transferring energy to Eu ions at indirect excitations. Based on photoluminescence observations, intra-4f transitions of Eu3+ ions at an excitation wavelength of 390nm allow a sharp red luminescence. Also the results showed that optical properties of ZnO can be tuned by varying the amount of Al concentration. In comparison with annealed Al doped ZnO:Eu nanostructures, as-grown samples showed the stronger PL peaks which indicated the effective role of intrinsic defects beside of extrinsic doping on energy transfer from ZnO host to Eu3+ ions which consequently led to producing the strong red emission from these sites.

Optical and photoluminescence properties of ZnO(1-x)Se(x) thin films.

ZnO(1-x)Se(x) (0≤x≤0.11) thin films have been grown on sapphire (c-Al₂O₃) substrates at the temperature of 350°C by means of the radio-frequency magnetron sputtering technique. The optical transmission, reflectance, and luminescence spectra at room temperature were analyzed. Using the λ-modulation method gives the possibility to reveal the main features of the energy band structure and the nature of the radiative transitions that cause ultraviolet luminescence.

Photoluminescence Property of ZnO:Eu Hollow Nanofibers Fabricated by Sputtering Using Electrospun PVP Nanofibers as Templates

Eu-doped ZnO (ZnO:Eu) hollow nanofibers were fabricated by sputtering using electrospun PVP nanofibers as templates. The morphologies, crystal configuration, bonding structures and optical properties of the ZnO:Eu hollow nanofibers were characterized, respectively. Raman results indicate that there are many oxygen vacancies and/or interstitial zinc in ZnO:Eu hollow nanofibers. Effect of Eu-doping on vibrating modes of ZnO is attributed to the change of defects and impurities due to incorporation of europium. The high intensity ultraviolet emission and red luminescence of the ZnO:Eu hollow nanofibers are observed due to the random lasing of near-band-gap emission of ZnO and an f-f transition of the Eu3+ions, respectively.

Structural, electrical and photoluminescence properties of ZnO:Al network films grown on nanochannel Al2O3 substrates by direct current magnetron sputtering with an oblique target

ZnO:Al network films were grown on nanochannel Al2O3 substrates at 300K by direct current magnetron sputtering with an oblique target. The film thicknesses are 60nm, 160nm and 190nm. The holes of the network films diminish with increasing film thickness. For the 60-nm thick film, the network is formed by connecting grains. For the 160-nm and 190-nm thick films, however, the network is formed by connecting granules. The granules consist of many small grains. All the network films have a wurtzite structure. The 60-nm and 160-nm thick network films mainly have a [101] orientation in the film growth direction while the 190-nm thick network film grows with a random crystallographic orientation. A temperature dependence of the resistance within 160–300K reveals that the network films exhibit a semiconducting behavior and their carrier transport mechanism is thermally activated band conduction. Room temperature photoluminescence spectra for wavelengths between 300nm and 700nm reveal a violet emission centered at 405nm for the 60-nm thick network film and a blue emission centered at 470nm for both the 160-nm and the 190-nm thick network films. Annealing decreases the resistivity of the network film.

Emergence of blue emission with decreasing film thickness and grain size for ZnO grown via thermal oxidation of Zn-metal films

ABSTRACTWe have investigated the photoluminescence properties of ZnO grown on sapphire substrates via the thermal oxidation of Zn-metal films at various temperatures and thicknesses. X-ray diffraction (XRD) spectra indicate that the resulting films possess a polycrystalline hexagonal wurtzite structure without preferred orientation. For films having a thickness of 200 nm, crystal grain size was observed to decrease with increasing annealing temperature up to 600ºC, and then increase at higher temperatures. Thicker films demonstrated a modest increase in grain size as temperature increased from 300ºC to 1200ºC. The influence of film thickness on the optical properties was investigated using room temperature photoluminescence (PL). Specifically, PL spectra indicate four emission bands: excitonic ultraviolet, blue, and deep-level green and yellow emission. The strongest UV emission and narrowest full width at half maximum (0.09 eV) was observed for films having a thickness of 200 nm and annealed at low temperature (300ºC). As film thickness decreased, we observed the emergence of blue emission. The emergence of blue emission when depletion width grows relative to the bulk suggests that the origin of the blue emission is related to the negatively charged Zinc interstitials found within the deletion region near the interface.

STRUCTURAL AND PHOTOLUMINESCENCE PROPERTIES OF Co:ZnO NANOCRYSTALLINE POWDERS

In the present study, results concerning the structural and photoluminescence properties of ZnO:Co nanocrystalline powders synthesized using an oxalate precursor decomposition method are reported. The XRD profiles reveal that all the samples are in hexagonal wurtzite structure. The values of the lattice parameters a and c are found to be decreasing linearly with Co content change. Surface morphological studies have also been carried out using SEM and TEM analyses. The origin of photoluminescence from ZnO and Co:ZnO has been reported.

Structural, electrical and photoluminescence properties of ZnO:Al films grown on MgO(0 0 1) by direct current magnetron sputtering with the oblique target

ZnO:Al films were deposited on MgO(0 0 1) substrates at 300 K and 673 K by direct current magnetron sputtering with the oblique target. The Ar pressure was adjusted to 0.4 Pa and 1.2 Pa, respectively. All the films have a wurtzite structure and a c-axis orientation in the film growth direction. The films deposited at 300 K initially grow with thin columnar grains and subsequently grow with large granular grains on the thin columnar grains. However, the films grown at 673 K consist mainly of dense columnar grains perpendicular to the substrate surface. The ZnO:Al film deposited at 673 K and 0.4 Pa has the lowest resistivity, the highest free electron concentration and Hall's mobility. A temperature dependence of the resistivity within 5–300 K reveals that the films grown at 300 K exhibit a semiconducting behavior and those grown at 673 K show a metal–semiconductor transition. The carrier transport mechanism is Mott's variable range hopping in the temperature range below 90 K for all the films and thermally activated band conduction above 215 K for the films grown at 300 K. Room temperature photoluminescence spectra for wavelengths between 300 nm and 800 nm reveal mainly blue-green emissions centered at 452 nm, 475 nm and 515 nm.

Investigation of photoluminescence mechanisms of ZnO through experimental and first-principles calculation methods

The photoluminescence properties of ZnO were investigated experimentally and by a first-principles method. Thermal treatment of ZnO in various atmospheres provides insight into the ultraviolet (UV) and green emission mechanisms. These mechanisms were investigated in detail from the thermal quenching behavior of the emission spectra of ZnO. The negative thermal quenching of the green emission could be fitted exactly with a model equation based on the assumption that UV emission loss by thermal quenching affects green emission. The electronic states of ZnO clusters with and without an oxygen vacancy were calculated by first-principles calculations using the discrete variational (DV) Xα molecular orbital method. This method gave a reasonably accurate calculation of band-gap energy. The energy levels calculated by the DV-Xα method agree well with experimentally measured thermal quenching activation energy and the zero-phonon energy of green emission. The results indicate that oxygen vacancies function as luminescent centers for green emission.

Ternary ZnO/ZnS/γ-Fe 2O 3 hollow sphere with surface hole: Microwave-enhanced rapid synthesis, bifunctional property, and immobilization of serum protein

High-yield ternary ZnO/ZnS/γ-Fe 2O 3 hollow spheres with an average size of 600 nm were prepared rapidly via a microwave-irradiation route; the reaction period is as short as 30 min. The hollow spheres are composed of numerous ZnO, ZnS, and γ-Fe 2O 3 crystallites and the mechanism responsible for their formation is Ostwald ripening. Every hollow sphere has a distinct surface hole with the pore size of tens of nanometers or hundreds of nanometers. The characterizations of the physical properties of the hollow spheres reveal that they have integrated the superparamagnetism of γ-Fe 2O 3 and the photoluminescence property of ZnO and ZnS. Furthermore, since the pore size of the hole on the surfaces of the hollow spheres is large enough to accommodate bovine serum albumin (BSA) molecule with a giant size, the hollow spheres can not only adsorb BSA with their external surfaces but also trap the proteins in their interiors. Per gram hollow sphere can immobilize 178.6 ± 34.5 mg of BSA when they are interacted with 600 μg/mL BSA solution for 24 h. The investigations on the releasing behavior of BSA by the hollow spheres reveal that BSA molecules on the external surfaces of the spheres are desorbed quickly, while those confined in the interiors of the spheres are released smoothly and the process is sustained over 10 days. The accumulative releasing percentage of BSA is about 51% in 10 days.

Green hydrothermal synthesis and photoluminescence property of ZnO 2 nanoparticles

ZnO 2 nanoparticles were synthesized via a green hydrothermal method using ZnO powder and 30% H 2O 2 aqueous solution as the starting materials, and characterized by X-ray diffraction (XRD), Raman spectra, energy dispersive X-ray (EDX) spectra, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and room temperature photoluminescence (RTPL) spectra. It was found that suitable reaction temperature (e.g., 80–140 °C) played an important role in obtaining pure cubic phase ZnO 2 nanoparticles. The RTPL spectra disclosed that the as-synthesized ZnO 2 nanoparticles exhibit one strong emission band centered at around 400 nm and one very weak emission band at around 474 nm, which may have originated from the band edge emission and the oxygen vacancy, respectively.

Erbium concentration effects on the structural and photoluminescence properties of ZnO:Er films

Films of Er-doped ZnO (ZnO:Er) were prepared on MgO(100) wafers by ultrasonic spray pyrolysis at 550 °C. The concentration of Er in the deposition source varied from 1.0 to 3.0 wt.%. The crystallographic properties and surface morphologies of the films were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Polycrystalline films were grown with a dominant direction of [002]. The grain size of the films was reduced by Er-doping. The ultraviolet (UV) photoluminescence properties of the films as a function of Er concentration were studied at low temperature (18 K) and room temperature (300 K). In undoped ZnO films, UV peaks at 3.375 and 3.360 eV were observed at 18 K, which are considered to be due to free excitons and donor-bound excitons, respectively. The peaks from the free exciton transitions disappeared at room temperature. Er-doping enhanced the room temperature UV emission of ZnO:Er films. ZnO:Er (2.0 wt.%) films prepared from the deposition source including 2.0 wt.% Er showed UV peaks which were ∼ 15 times stronger than those of undoped ZnO films.

Electro- and photoluminescence of the Tm 3+ ion in Tm 3+- and Li +-doped ZnO ceramics. Influence of the sintering temperature

The electro- and photoluminescence properties of ZnO:Tm,Li pellets sintered between 900 and 1300°C have been studied at room temperature. The photoluminescence spectra show the emissions arising from both the Tm 3+ ions and ZnO itself whereas the electroluminescence spectra show only the emission arising from the Tm 3+ ions. The dependence of the current, capacitance and luminescence intensity upon voltage was measured. As for the ZnO:Bi composites, the electro-optical properties of the ZnO:Tm,Li composites depend mainly upon the grain boundaries, but unlike for the ZnO:Bi composites, they cannot be interpreted in terms of a succession of grain boundaries barriers. It is concluded that the grain boundaries act as preferential conduction pathways. The Tm 3+ ions are mainly located between the grains in intergranular layers where their luminescence acts as a probe, which evidences both the current flow and the presence of hot electrons.