Ultraviolet Emission Peak Research Articles

Synthesis and physicochemical properties of graphene incorporated indium tin oxide nanocomposites for optoelectronic device applications

In this work, we synthesized graphene (g) – incorporated Indium Tin Oxide (ITO) and investigated its structural, morphological, electrical, optical and magnetic properties. The ITO materials, including the 1 % and 2 % g-ITO variants, have a cubic crystal phase, while graphene possesses a hexagonal lattice structure. The Raman spectra exhibited distinct ITO peaks, along with the presence of active modes such as A1, E1, and Eg associated with the CC stretching peak. UV-DRS was performed to study the optical absorption properties in the range of 200–900 nm for the as-prepared ITO, ITO-g (1 %), and ITO-g (2 %) composites. The composite exhibited energy absorption at wavelengths of 320, 314, and 312 nm for ITO, ITO-g (1 %), and ITO-g (2 %), respectively. The photoluminescence spectra exhibited a prominent ultraviolet emission peak at a wavelength of 374 nm as well as a blue-green emission peak at 446 nm, which were found in both the pure and doped samples. Finally, electrical and magnetization was conducted on both unadulterated and g-ITO.

Scalable nano-integration strategy: Controllable three-dimensional monocrystalline GaN nanostructures from nanobelts to nanonetwork

The effective and scalable assembly of 1D nano-units into ordered 3D monocrystalline networks remains a challenge. Based on the crystal structure and growth characteristics of GaN, we have designed a specific epitaxy strategy and successfully achieved large area self-networking of 3D monocrystalline nanostructure on Au-coated β-LiGaO2 (100) substrate formed by the interconnection of GaN nanobelts grown along three equivalent directions of the m-axis [011̅0], [101̅0] and [11̅00]. This well-aligned 3D GaN nanostructure grown by simple CVD method has good reproducibility and the yield of cross-linked junctions are quite high. The mono-crystallinity of this structure were proved by X-ray diffraction (XRD) and transmission electron microscope (TEM) results, especially at the crosslinked junctions. The overall epitaxial relationships between GaN and LiGaO2 was analyzed and the defect-mediated anisotropic VS growth mechanism was deduced from thorough characterization of individual nanobelts. Besides, the morphology of 3D GaN nanostructure including length, width and height was found to be controllable. The E2 (high) phonon peak at 567.4 cm−1 in the Raman spectrum and the strong ultraviolet emission peak centered at 363.3 nm (3.41 eV) in the photoluminescence (PL) spectrum indicate that the 3D GaN nanostructures are nearly strain-less and have high crystalline quality. This large-scale 3D monocrystalline network not only retains the advantage of 1D nanomaterials, but also become easier to operate compared with individual nanowire. The epitaxy assembly strategy is expected to ensure the property homogeneity of chip-scale devices for their real applications and provide a reference for further growth of tunable 3D structures of other materials.

The preparation of CuO film under different annealing atmospheres and investigation of the excellent electrical and undoped tunable electroluminescence characteristics of Au/i-CuO/n-GaN LED

Copper oxide (CuO) film is widely used in optoelectronic devices. The CuO films were fabricated by radio frequency (RF) magnetron sputtering and then annealed at 700 °C under different atmospheres (unannealed, O2, N2, vacuum). The physical characteristics of the films were analyzed systematically. In addition, we prepared Au/i-CuO/n-GaN metal-insulator-semiconductor (MIS) structure devices using optimized conditions. The devices had excellent rectifying characteristics at different ambient temperatures and the turn-on voltage was about 1.7 V. The working mechanism of the diode was analyzed through electroluminescence (EL) spectra and band structure. The EL spectra observed at positive and negative bias were compounded by holes and electrons on the gold electrode passing through the insulating layer into the n-GaN side. The EL spectra exhibited that a dominant ultraviolet (UV) emission peak at ∼376 nm was observed under forward bias (FB), and a strong near-white light emission peak at ∼530 nm was observed under reverse bias (RB). The device exhibited unique electroluminescent spectra tunability varying with bias conditions. The chrominance coordinate of the device under RB was (0.3067,0.3604), and the color temperature was 6585 K. This study proved the application potential of i-CuO as an insulating layer in the preparation of new reference for MIS structured GaN-based tunable light-emitting diodes.

Further Characterization of the Polycrystalline p-Type β-Ga2O3 Films Grown through the Thermal Oxidation of GaN at 1000 to 1100 °C in a N2O Atmosphere

The development of good-conductivity p-type β-Ga2O3 is crucial for the realization of its devices and applications. In this study, nitrogen-doped p-type β-Ga2O3 films with the characteristics of enhanced conductivity were fabricated through the thermal oxidation of GaN in a N2O atmosphere. To obtain insights into the underlying mechanism of the thermally activated transformation process, additional measurements of the oxidized films were performed at temperatures of 1000, 1050, and 1100 °C. Room-temperature photoluminescence (PL) spectra showed a moderate ultraviolet emission peak at 246 nm, confirming the generation of gallium oxide with a band gap of approximately 5.0 eV. The characteristics of polycrystalline and anisotropic growth were confirmed via normalized X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED) patterns. The amount of incorporated nitrogen was analyzed via secondary ion mass spectrometry (SIMS) to examine the effects of oxidation temperature. Furthermore, the ionization energy of the acceptor in the films oxidized at 1000, 1050, and 1100 °C was calculated and analyzed using temperature-dependent Hall test results. The results indicated that nitrogen doping played a significant role in determining p-type electrical properties. The activation energy of polycrystalline β-Ga2O3, prepared via the thermal oxidation of GaN in the N2O atmosphere, was estimated to be 147.175 kJ·mol−1 using an Arrhenius plot. This value was significantly lower than that obtained via both the dry and wet oxidation of GaN under O2 ambient conditions, thus confirming the higher efficiency of the thermal oxidation of GaN in a N2O atmosphere.

Synthesis and investigation of the physicochemical properties of polymorphic 3C–SiC

Silicon carbide (SiC) nanopowders were synthesized under Ar atmosphere via the carbonization reaction method using silicon powders and expanded graphite as initial materials, and ferric nitrate as catalyst precursor. The effects of heat treatment temperature and the C/Si molar ratio on SiC products were studied. The microstructure, phase composition and chemical state of the products were analyzed by XRD, SEM, XPS, TEM and Raman. The photoluminescence (PL) properties of SiC nanopowders were tested. The results showed that the content of the 3C–SiC product is higher after heat treatment at 1400 °C for 3 h with a molar ratio of C/Si of 1:1. 3C–SiC exists in the form of particles and wires. The formation process of 3C–SiC can be explained by a two-step method, nucleation under catalysis and growth under Vapor-Solid (VS) mechanism. Two ultraviolet light emission peaks are observed at about 318 and 380 nm. The main PL spectra of 3C–SiC nanopowders exhibit larger blueshifts. The blueshift is attributed to the stacking fault, oxygen defects, morphology and quantum confinement effect. It has potential application prospects in ultraviolet detectors, optoelectronic devices and light emitters.

Electronic, structural and optical properties of Gd-doped ZnO powder synthesized by solid-state reaction method

We explored the impact of Gd doping on the structural, electronic and optical characteristics of the ZnO powder. The Gd-doped ZnO (0, 2% and 5%) powder samples have been synthesized using the conventional solid-state reaction process with varied Gd concentrations. The XRD pattern confirmed that all the studied samples are in the hexagonal wurtzite crystalline structure. The morphology has been explored using SEM images, which exhibited an agglomerated rod-like particle structure. The XPS results indicate the presence of oxygen vacancies (Vo) in the Gd-doped ZnO samples and the Vo’s are found to increase with increasing Gd amount. According to PL findings, the intensity ratio of the green and ultra-violet emission peaks is found to increase from 0.090 to 0.418 with increasing Gd-doping concentrations, confirming that Vo’s are increasing with Gd-doping. The UV-visible spectroscopy results reveal that the energy band gap (Eg) decreased from 3.31 eV to 3.23 eV with increasing Gd-doping concentration. Bangladesh J. Sci. Ind. Res. 58(1), 53-64, 2023

Effect of (Ce, Dy) co-doping on the microstructural, optical and photoluminescence characteristics of solution combustion synthesized ZnO nanoparticles.

Solution combustion synthesized ZnO nanoparticles with Ce, Dy doped and co-doped with varying dopant concentrations were characterized for their microstructural, optical and photoluminescence characteristics. The synthesized nanoparticles have been found to match the standard hexagonal wurtzite structure of ZnO. The lattice fringes in the high-resolution transmission electron micrographs and the bright spotty rings in the selected area electron diffraction pattern authenticate the high crystallinity of the nanoparticles. The diffuse reflectance spectroscopy provides the energy bandgap for the undoped ZnO to be 3.18 eV, decreasing upon doping and co-doping. A sharp narrow UV emission peak at ~ 398 nm originating from the excitonic recombination is found in the PL spectra of the nanoparticles. The visible emission peaks in the PL spectra are assigned to f-d and f-f electron transitions of Ce3+ and Dy3+ ions, respectively, in addition to different native defects in ZnO. The visible emissions (blue, yellow and red) have been found to improve upon (Ce, Dy) co-doping, and therefore (Ce, Dy) co-doped ZnO nanoparticles can be considered as a promising luminescent material for the development of energy-saving light sources.

UV luminescence enhancement of Cu-doped ZnO nanorods grown by hydrothermal treatment

Herein, we studied the effect of Cu doping on the ultraviolet (UV) emission enhancement of ZnO nanorods. ZnO nanorods with different Cu doping concentrations were prepared by hydrothermal method and the Cu doping behavior was investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ultraviolet visible (UV–Vis) absorption spectroscopy and photoluminescence (PL). XRD patterns confirmed the incorporation of Cu. Compared with pure ZnO, no other phase appears, the intensity of diffraction peaks and the calculated parameters such as lattice constants increase, all of which proved that the doping of Cu is substitutional doping. Doping induces a red-shift in the absorption maximum wavelength of the absorption spectrum, indicating that doping causes attenuation of UV absorption properties. In the PL spectra, the increase of Cu doping concentration makes the UV emission peak enhanced and there is almost no emission peak in the visible region. The UV emission at room temperature can be attributed to the superposition of free and bound excitons, where free excitons dominate and bound excitons are related to the substitution of Cu for Zn. The enhanced UV emission of Cu-doped ZnO materials could lead to the wide application in the field of UV optoelectronic devices.

Ultraviolet emissive Ti3C2Tx MXene quantum dots for multiple anti-counterfeiting

The development of advanced anti-counterfeiting is an important and urgent task for civil, commercial and military applications. Herein, multiple anti-counterfeiting was performed by using the dispersion of Ti3C2Tx MXene quantum dots (MQDs) as luminescent ink. The ultraviolet emissive MQDs were prepared for the first time by decreasing their oxidation degree. Compared with the MQDs obtained by the microwave heating, the oxidation degree of the MQDs treated by ethanol refluxing reduced from 38% to 23%, the ultraviolet emission peak blue-shifted from 307 to 299 nm, and the quantum yield raised by four times. Simultaneously, the colloidal stability, photostability, thermal stability and pH stability were also greatly enhanced. Based on the excitation-dependent luminescence properties of the MQDs with low oxidation degree, multiple anti-counterfeiting was developed using the colorless and transparent MQD dispersion. The concealed pattern was recognized for a preliminary judgement by bare-eyes with the illumination of a 365 nm ultraviolet lamp, resulting from the blue luminescence of MQDs. As for the high-level anti-counterfeiting, a more legible ultraviolet luminescent pattern was presented by an adaptive focus imaging spectrograph with 254 nm excitation. This study unlocks the ultraviolet photoluminescence of MQDs and furnishes a novel candidate for advanced anti-counterfeiting.

A novel photoluminescence phenomenon in a SrMoO4/SrWO4 micro/nano heterojunction phosphors obtained by the polyacrylamide gel method combined with low temperature calcination technology

The polyacrylamide gel method combined with low temperature calcination technology have been used to synthesize the SrMoO4/SrWO4 micro/nano heterojunction phosphors with excellent photoluminescence properties. The effects of mass ratio of SrMoO4/SrWO4 on the phase structure, microstructure, charge state, photoluminescence performance and photocatalytic activity of SrMoO4/SrWO4 phosphors were systematically studied. Various characterization methods jointly confirmed that SrMoO4 and SrWO4 formed a special interface contact, generated a large number of oxygen vacancies, and then promoted the transfer and recombination of charge carriers, and further enhanced the photoluminescence properties of SrMoO4/SrWO4 micro/nano heterojunction phosphors. The SrMoO4/SrWO4 micro/nano heterojunction phosphors exhibits novel emission peak at 440 nm with the excitation wavelength of 310 nm and the ultraviolet intrinsic emission peak at 378 nm of SrMoO4. Photocatalytic experiments further confirmed that the SrMoO4/wt 5% SrWO4 micro/nano heterojunction phosphors have high charge transfer and recombination rates, demonstrating high photoluminescence properties for the SrMoO4/SrWO4 micro/nano heterojunction phosphors. This new idea provides a technical reference for the construction of heterojunction phosphor with special interface contact and its application in LED and laser fields.

Study of well-aligned Ag@ZnO nanoflower arrays with growth, photoluminescence and ultrafast nonlinear absorption properties

ZnO nanoflowers (NFs) and silver-decorated ZnO ([email protected]) NFs arrays were prepared by two/three-step progress of magnetron sputtering, hydrothermal and magnetron sputtering method, respectively. The effect of silver nanoparticles (NPs) on the visible emission performance of ZnO arrays was described. The results show that the ultraviolet emission (UVE) peak of ZnO NFs array is concentrated at 380 nm red-shifted to longer wavelength after being decorated with Ag NPs in the diameter of 18–50 nm. It is very interesting that the intensity of the visible emission (VE) is enhanced by the VE ratio of 1.43 for the [email protected] NFs arrays of 0.03 mol/L. However, for the [email protected] NFs arrays of 0.015 mol/L, the UVE peak blue shift from 387 nm to 384 nm, indicating a slight decrease in emission intensity due to the decorating Ag NPs of 10–20 nm. The enhancement of VE is considered as the synergistic effect of competition between the increase of exciton concentration and the enhancement of Ag NPs local field. The Z-scan measurement of the opening was performed at 800 nm, revealing the contribution of metal NPs. [email protected] NFs arrays with remarkable nonlinear optical properties are a potential nanomaterial for the development of multifunctional optoelectronic devices.

Preparation of Carbon Nanodots with Ultraviolet Emission by Pulsed Laser Ablation

To date, it is still a challenge to acquire carbon nanomaterials with ultraviolet (UV) emission due to the trapping of excited carriers by defect states and surface groups. Herein, a pulsed laser ablation (PLA) method without any post‐treatments is developed to prepare carbon nanodots (CNDs). The cores of the resulting CNDs are graphitic carbon with negligible defects, whereas the surfaces are passivated by simple oxygen‐related groups, which is demonstrated by high‐resolution transmission electron microscope (HRTEM) image, X‐ray diffraction (XRD) pattern, and Raman spectra. Thus, the trapping of excited carriers by defect states and surface groups is substantially suppressed. As a consequence, the CNDs exhibit inherent UV emission of carbon nanostructures. The excitation‐independent UV emission peak contains three sub‐bands at 305, 325, and 335 nm. This work develops an approach for the preparation of UV‐emissive CNDs, which expands the applications of CNDs to UV‐related areas.

A method for effectively regulating the green emissions of ZnO through NiS@NiO/rGO

In this study, a ZnO/NiS@NiO/rGO (ZNNG) composite was characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). Compared with simple ZnO, ZNNG exhibited stronger green emissions, but no ultraviolet (UV) emission peak was observed. Through a comprehensive analysis of ultraviolet–visible (UV–vis) absorption spectra, Mott Schottky (MS) plots, electron paramagnetic resonance (EPR) spectra, and X-ray photoelectron spectroscopy (XPS) results, it was proved that the stable green emissions of ZnO and its composites originated from the quenching of electrons between Zn interstitial (Zni) and surface oxygen defects. The introduction of NiS@NiO caused the conduction band (CB) and valence band (VB) of ZnO to change to lower energy states, effectively increasing the absorption intensities of ZnO in the visible light, while introducing numerous oxygen-related defects on the surface of ZnO. Further addition of rGO effectively promoted the migration of electrons from the CB to the Fermi energy (Ef). These effects effectively increased the green emission of ZnO and reduced the UV emission. Finally, a proper mechanism for the near-zero band gap NiS@NiO/rGO that can significantly enhance the green emission of ZnO was proposed.

Optimization and characterization of SILAR synthesized ZnO nanorods for UV photodetector sensor

In the current research, zinc oxide (ZnO) nanorods (NRs) have been grown upon glass-slide substrates by employing the effective chemical bath deposition (CBD) method at low-temperature. ZnO seed-layer has been coated over the whole substrates by using very simplicity successive ionic-layer adsorption and reaction (SILAR) approach. The impact of the four different SILAR process cycle for ZnO seed-layer deposition on the characteristic of ZnO NRs have been investigated. The surface morphological, structural, optical properties of the produced ZnO NRs have been studied using several techniques for different SILAR process cycles. Also, the high-quality UV photodetector (PDs) based on ZnO NRs at different SILAR process cycles have been successfully fabricated by applying bias voltage in range of (-5 V to 5 V). The results indicated that the variation of SILAR process cycles have the large and significant impact on the morphological, structural, and optical properties of ZnO NRs. The average size and length of fabricated ZnO NRs were increased with increases the SILAR cycles in the range of 32−98 nm and 291−1210 nm, respectively. The large aspect ratio was noted for ZnO NRs formed at 15 SILAR cycles about 14.93. The growth rate and crystal size of ZnO NRs were increases with increases the SILAR cycles in the range of 1.161–6.722 nm/min and 28.9–94.24 nm/min, respectively. All the samples display a dominant peak at wavenumber of 436.5 cm−1 which is attributed to the E2 active mode and characteristic of the hexagonal phase of ZnO NRs. The energy gap of ZnO NRs was decreased from 3.25 eV to 3.23 eV as the SILAR cycles increases from 5 cycles to 20 cycles. The overall ultraviolet (UV) emission peak centered at 380 nm is found to correlate to near-band emissions (NBE). The ZnO NRs based UV-detector displays repeatable characteristics with a peak photoresponse of 116.6 μA. The UV-sensor based ZnO NRs grown at 15 SILAR process cycles at 5 V bias voltage shows optimal performance responsivity, high photosensitivity, low dark current, quick rise and recovery times were 0.5477 A/W, 3573.57 %, 3.1743 μA, 1.04259 s, and 0.3046 s, respectively.

Optical properties of CuO/ZnO composites prepared by mechanical grinding

In this work, ZnO and CuO were first prepared by thermal evaporation and direct precipitation, respectively, and then CuO/ZnO composites were obtained by mechanical grinding the mixtures of CuO and ZnO. Scanning electron microscopy, Raman spectroscopy, Raman imaging, UV–vis absorption spectroscopy, and photoluminescence spectroscopy were used to analyze the morphology, structure, and optical properties of CuO/ZnO composites. Raman spectra suggest that the prepared ZnO has a high crystalline quality, while the CuO/ZnO composites have an internal stress. Compared with ZnO, the absorption edge of CuO/ZnO composites shows a red-shift, and the absorption intensity in the visible region is increased greatly. Pure ZnO shows a strong ultraviolet (UV) emission and a weak green emission. As for the CuO/ZnO composites, with the increase of CuO content, the intensity of the UV emission is gradually reduced and the UV peak is gradually moving towards the longer wavelength direction. The decrease in the UV emission intensity should be attributed to interface effects, and the red-shift of UV emission peaks may be caused by unintentional Cu-doping.

Growth evolution and customized attributes of catalyst-free ZnO nanowires: role of varied Ar/O2 flow rate

This paper reports a tailored structure, morphology, optical behavior, and growth evolution of catalyst-free ZnO nanostructures (ZONSs) synthesized on quartz substrates using the wet thermal evaporation method. The as-prepared samples were thoroughly characterized to determine the influence of varying rates of Ar and wet O2 gas flow (150, 250, and 350 sccm) on their overall properties. Scanning electron microscopy (SEM) images revealed the formation of high-quality ZONSs of various shapes, including nanowires, aligned nanorods, and nanorods-like tetrapods with different dimensions. X-ray diffraction (XRD) patterns displayed the most intense diffraction peak at (002), which was attributed to the preferred growth orientation and crystallinity of such nanomaterials. Photoluminescence (PL) spectra showed an enhancement in the peak intensity. The position of the ultraviolet emission peak of ZONSs was red-shifted as the gas flow rate increased. Raman spectra exhibited the high-intensity E2 and very weak (suppressed) E1L Raman mode for all samples, indicating the accomplishment of good crystal quality in wurtzite hexagonal crystalline ZONSs of the samples. Furthermore, the optimum flow rate for synthesizing high-density, superior quality, and higher nanocrystalline ZONSs was found to be 350 sccm. This work can contribute toward the development of the production of various nano-optical devices.

Large enhancement in UV emission and photocatalytic performance of Al-doped Co3O4Nanostructures under visible light

The luminescence and photocatalytic performance of cobalt oxide (Co3O4) nanostructures have been widely discussed. However, the study of ultraviolet (UV) luminescence and visible photocatalytic activity of metal (Al) doped Co3O4 has not been considered till date. In this study, we produce a series of cubic Al-doped Co3O4 nanoparticles (NPs) synthesized by chemical route. The photoluminescence spectrum of pure Co3O4 sample shows UV emission as well as visible emission peaks while on the incorporation of Al3+ ion, only intense UV emission peak around 399 nm (3.10 eV) is observed with quenched DLEs in all doped Co3O4 samples. Though, the intensity of UV emission peak is found high as nine fold of the pure sample in all doped samples which have been affected by the density of free excitons induced by the Al doping. Also, photocatalytic degradation of reactive blue-171 (RB-171) dye was studied under visible light using pure and doped Co3O4 samples as a catalyst which possess extraordinarily enhanced visible photocatalytic performance. Therefore, due to considerable enhancement in UV emission and photocatalytic performance, we suggest that Al-doped Co3O4 NPs play a significant role in the applications of strong UV luminescence devices, electrochromic devices as well as photocatalytic utilizations.

Copper decorated ZnO nanowires material: Growth, optical and photoelectrochemical properties

Abstract To reveal the photoelectricchemical (PEC) properties modulation and its mechanism is beneficial to the exploration of novel materials with excellent properties as well as the realization of their practical application. In this paper, uniform copper-decorated ZnO nanowires (Cu@ZnO NWs) were successfully prepared via the two-step chemical vapor deposition and then magnetron sputtering method. The structure, morphology, and composition of Cu@ZnO NWs at different sputtering time (ST) and sputtering power (SP) were characterized. The result of morphology characterization show of Cu on the surface ZnO NWs can be controlled by ST and SP adjustment. The optical and PEC properties of Cu@ZnO NWs were studied. All samples showed a strong linear absorption band due to the inherent absorption band of the ZnO nanowires in the near-ultraviolet range. The addition copper did not make any significant difference in its band gap. However, due to the surface plasmon resonance (SPR) absorption of the Cu nanostructures, the absorption spectrum peak at 558 nm is exhibited. The photoluminescence (PL) results proved two emission peaks for the Cu@ZnO NWs, which the sharp ultraviolet (UV) emission peak corresponding to the near band edge emission, and broad visible range originates from the electron-hole recombination at a deep level, caused by oxygen vacancy or zinc interstitial defects and the UV/visible emission peaks of Cu@ZnO NWs are weaker/stronger than that of pure ZnO nanowires. The PEC characteristics showed an increase/decrease in the current density of Cu@ZnO Nws with different ST/SP compared to that of unmodified ZnO nanowires. The experimental result shows that the PL and PEC properties of ZnO nanowires were regulated by Cu nanostructures with different morphologies. The ease of the synthesis route and the remarkable PL and PEC properties offer metal-semiconductor compound nanostructure materials as a promising electron source for high current density applications.

Cation impurity-defect complex induced ferromagnetism and hopping conduction in Sb-doped ZnO synthesized under high pressure

Sb-doped p-type ZnO was synthesized using the high-pressure method with a quasi-equilibrium thermodynamic process. Room temperature ferromagnetism was observed in Sb-doped ZnO. The ferromagnetic coupling was found to be associated with zinc vacancies (VZn) induced by Sb doping, which was supported by a strong ultraviolet emission peak relevant to VZn in low temperature photoluminescence. Hall effect measurements indicated that the Sb-doped ZnO with Sb content of 3.4 at% had a hole concentration of 1.4 × 1020 cm−3 and low resistivity of 7.4 × 10−2 Ω cm. Temperature-dependent resistance measurements suggest that the electrical conduction mechanism of the Sb-doped ZnO changed from thermal activation model and nearest-neighbor hopping (NNH) conduction at high temperature to Mott variable-range hopping (VRH) and Efros–Shklovskii VRH conduction at low temperature. First-principles calculations demonstrated that the Sb impurity substituting Zn (SbZn) combines two VZn defects to form acceptor-like impurity-defect complex of SbZn–2VZn in ZnO due to the coulomb attraction. The SbZn–2VZn complex in Sb-doped ZnO are strongly correlated with ferromagnetic stability and lead to the Mott and Efro–Shklovskii VRH conduction at low temperature due to the localization of carriers at the complex impurity band.

Magnetic and optical properties of Co-doped ZnO nanorod arrays

In this study, Zn1−xCoxO nanorod arrays were deposited on Si substrates by magnetron sputtering followed by the hydrothermal method at 100 °C. The effects of doping concentration and hydrothermal growth conditions on the crystal structures, morphologies, magnetic and optical properties of the obtained Zn1−xCoxO nanorod arrays were studied. Surface characterization showed Zn1−xCoxO nanorod arrays with uniform and dense distributions along the [0001] direction with the hexagonal wurtzite structure. Besides, no impurity phases were detected in Zn1−xCoxO nanorod arrays. The room-temperature ferromagnetism of Zn1−xCoxO nanorod arrays was detected based upon the high-saturation magnetization of 4.4 × 10–4 emu/g, the residual magnetization of 1.1 × 10–4 emu/g and the coercive field of 309 Oe. Furthermore, the photoluminescence (PL) spectra exhibited by the Zn1−xCoxO nanorod arrays with the luminescence intensity in the ultraviolet region were nearly five times that of the pure ZnO nanorod arrays. With the increase in the Co2+ doping concentration, the redshift in the ultraviolet emission peaks was observed. The theoretical results presented obvious spin polarization near the Fermi level, with strong Co 3d and O 2p hybridization effects. The magnetic moments were mainly generated by Co 3d and partial contribution of O 2p orbital electrons. These results indicated that Zn1−xCoxO nanorod arrays can be used as potential magneto-optical materials.