Study of Ar + O2 deposition pressures on properties of pulsed laser deposited CdTe thin films at high substrate temperature

Cadmium telluride (CdTe) thin films deposited by pulsed laser deposition (PLD) on fluorine–tin–oxide substrates under different pressures of argon (Ar) + oxygen (O₂) at high substrate temperature (T_s = 500 °C) was reported in this paper. In our work, the CdTe thin films were prepared successfully at high T_s by inputting Ar + O₂. As reported, PLD-CdTe thin films were almost prepared at low substrate temperatures (<300 °C) under vacuum conditions. The deposition of CdTe thin films at high T_s by PLD is rarely reported. The influence of the Ar + O₂ gas pressure on thickness, structural performance, surface morphology, optical property and band gap (E_g) had been investigated respectively by Ambios probe level meter, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectrometer. Strong dependence of properties on the deposition pressures was revealed. In the range of Ar + O₂ gas pressure from 5 to 12 Torr, the deposition rate and the E_g of CdTe films vary in the range of 41.9–57.66 nm/min then to 35.26 nm/min and 1.51–1.54 eV then to 1.47 eV, respectively. The XRD diagrams showed that the as-deposited films were polycrystalline, and the main phase was cubic phase. However, the preferred orientation peak disappeared when the deposition pressure was higher. SEM images indicated that the CdTe film deposited at a higher deposition pressure was more uniform and had a higher compactness and a lower pinhole density. Furthermore, based on this thorough study, FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe:Cu/Ag solar cells with an efficiency of 6.68 % and an area of 0.64 mm² were prepared successfully.     

Effects of growth temperature on electrical and structural properties of sputtered GaN films with a cermet target

GaN films have been deposited at 100–400 °C substrate temperature on Si (100) and sapphire (0001) substrates by RF reactive sputtering in an (Ar + N₂) atmosphere. A (Ga + GaN) cermet target for sputtering was made by hot pressing the mixed powders of metallic Ga and ceramic GaN. The effects of substrate temperature on the GaN formation and its properties were investigated. The diffraction results showed that GaN films with a preferential (10–10) growth plane had a wurtzite crystalline structure. GaN films became smoother at higher substrate temperature. The Hall effect measurements showed the electron concentration and mobility were 1.04 × 10¹⁸ cm^?3 and 7.1 cm² V^?1 s^?1, respectively, for GaN deposited at 400 °C. GaN films were tested for its thermal stability at 900 °C in the N₂ atmosphere. Electrical properties slightly degraded after annealing. The smaller bandgap of ~3.0 eV is explained in terms of intrinsic defects and lattice distortion.     

Influence of H2 introduction on properties in Al-doped ZnO thin films prepared by RF magnetron sputtering at room temperature

Al-doped ZnO (AZO) thin films were prepared by RF magnetron sputtering on quartz substrates at room temperature in different Ar + H₂ ambient. The influence of H₂ flow ratio on the structure and optoelectronic properties in AZO films was investigated. The prepared films are hexagonal wurtzite structure with c-axis preferred orientation, and the intensity of (002) peak decreases with the increase of H₂ flow ratio. The resistivity significantly decreases with increasing the H₂ flow ratio to 1.0 % by almost four orders of magnitude. X-Ray photoelectron spectroscopy and X-ray diffraction measurements exhibit that the effectiveness of Al doping in the substitutional positions is not influenced by H₂ addition. We suggest that there exist a large number of acceptors in the films, the introduced H₂ will passivate the acceptors, which raises both carrier concentration and Hall mobility. The increase of carrier concentration consequently induces the blue shift of optical absorption edge according to the Burstein-Moss effect.     

Ni–YSZ(111) solid–solid interfacial energy

Solid-state dewetting of continuous Ni films deposited on the (111) surface of yttrium stabilized zirconia (YSZ) was used to produce equilibrated Ni particles, and the solid–solid interface energy was determined using Winterbottom analysis. The ~150 nm thick Ni films were dewetted (annealed) at 1350 °C in Ar + H₂ (99.9999 %) at an oxygen partial pressure of 10^?20 atm for 6 h. Transmission electron microscopy of equilibrated particles was conducted, and two low-energy low-index orientation relationships were found: $ {\text{Ni[1}}\overline{ 1} 0 ] ( 1 1 1 )\left\| {{\text{YSZ[1}}\overline{ 1} 0 ]} \right. ( 1 1 1 ) $ and $ {\text{Ni[}}\overline{ 1} 1 0 ] ( 1 1 1 )\left\| {{\text{YSZ[1}}\overline{ 1} 0 ]} \right. ( 1 1 1 ) $ , and the interface energies were measured to be 1.8 ± 0.1 and 2.1 ± 0.1 J/m², respectively. A model including grain growth concurrent with dewetting is used to explain the formation of the higher energy orientation relationship.     

Few-layer graphene films prepared from commercial copper foil tape

We present a facile, versatile and cost-effective method for the synthesis of mono- and bilayer graphene films on copper substrate using as carbon feedstock the pyrolysis products of the conductive adhesive polymer of a commercial copper tape commonly used in electron microscopy. A copper tape with adhesive on both sides is subjected to a heat treatment during 15 min at temperatures of 900, 1000, and 1050 °C under the flow of an Ar + 3%H₂ gas mixture. With this treatment, the tape adhesive polymer is pyrolized and the interaction of its decomposition products with the copper substrate gives rise to a graphene film of good structural quality mixed with amorphous carbon residues of the pyrolysis. For a temperature of 1050 °C (few degrees below the melting point of Cu), mono- and bilayer coexisting domains of graphene are obtained with almost 100% area coverage of the Cu substrate. For lower heat treatment temperatures, area coverage is reduced to 60–70% and the graphene film becomes predominantly bilayer. The treatment at the lowest temperature of 900 °C results in isolated hexagonal domains of graphene intermixed with a large amount of amorphous carbon residues and large uncovered areas of oxidized copper substrate. These results indicate that the number of active species for the formation of graphene films increases with increasing temperature, nevertheless limited by the copper melting point. Characterization of the obtained samples was performed with scanning electron microscopy, Raman scattering, and high-resolution transmission electron microscopy.     

Exciting Dilute Magnetic Semiconductor: Copper-Doped ZnO

The present study is focused on the copper-doped ZnO system. Bulk copper-doped ZnO pellets were synthesized by a solid-state reaction technique and used as target material in pulsed laser deposition. Thin films were grown for different Cu doped pellets on sapphire substrates in vacuum (5×10^?5 mbar). Thin films having (002) plane of ZnO showed different oxidation states of dopants. M–H curves exhibited weak ferromagnetic signal for 1–3 % Cu doping but for 5 % Cu doped thin film sample showed the diamagnetic behavior. For deeper information, thin films were grown for 5 % Cu doped ZnO bulk pellet in different oxygen ambient pressures and analyzed. PL measurement at low temperature showed the emission peak in thin films samples due to acceptor-related transitions. XPS results show that copper exists in Cu²⁺ and Cu⁺¹ valence states in thin films and with increasing O₂ ambient pressure the valence-band maximum in films shifts towards higher binding energy. Furthermore, in lower oxygen ambient pressure (1×10^?2 mbar) thin films showed magnetic behavior but this vanished for the film grown at higher ambient pressures of oxygen (6×10^?2 mbar), which hints towards the decrease in donor defects.     

Antibacterial and bioactive calcium titanate layers formed on Ti metal and its alloys

An antibacterial and bioactive titanium (Ti)-based material was developed for use as a bone substitute under load-bearing conditions. As previously reported, Ti metal was successively subjected to NaOH, CaCl₂, heat, and water treatments to form a calcium-deficient calcium titanate layer on its surface. When placed in a simulated body fluid (SBF), this bioactive Ti formed an apatite layer on its surface and tightly bonded to bones in the body. To address concerns regarding deep infection during orthopedic surgery, Ag⁺ ions were incorporated on the surface of this bioactive Ti metal to impart antibacterial properties. Ti metal was first soaked in a 5 M NaOH solution to form a 1 μm-thick sodium hydrogen titanate layer on the surface and then in a 100 mM CaCl₂ solution to form a calcium hydrogen titanate layer via replacement of the Na⁺ ions with Ca²⁺ ions. The Ti material was subsequently heated at 600 °C for 1 h to transform the calcium hydrogen titanate into calcium titanate. This heat-treated titanium metal was then soaked in 0.01–10 mM AgNO₃ solutions at 80 °C for 24 h. As a result, 0.1–0.82 at.% Ag⁺ ions and a small amount of H₃O⁺ ions were incorporated into the surface calcium titanate layers. The resultant products formed apatite on their surface in an SBF, released 0.35–3.24 ppm Ag⁺ ion into the fetal bovine serum within 24 h, and exhibited a strong antibacterial effect against Staphylococcus aureus. These results suggest that the present Ti metals should exhibit strong antibacterial properties in the living body in addition to tightly bonding to the surrounding bone through the apatite layer that forms on their surfaces in the body.     

Thermal,structural and in vitro dissolution of antimicrobial copper-doped and slow resorbable iron-doped phosphate glasses

This paper focuses on investigating and comparing the effects of CuO and Fe₂O₃ addition on the bioactive response of glass having composition [xCuO or Fe₂O₃ + (100 ? x) (0.2CaO + 0.2SrO + 0.1Na₂O + 0.5P₂O₅)] (in mol%), where x is ranging from 0 up to 5. The addition of CuO was found to increase the hot processing window and the dissolution rate leading to a fast surface layer precipitation. Using IR and Raman spectroscopies, we related this change in the bioactive response of this glass to the progressive depolymerization of the glass network induced by the addition of CuO. On the other hand, the addition of Fe₂O₃ was found to reduce the hot processing window and the dissolution rate as no depolymerization of the network occurs due to the formation of P–O–Fe bonds at the expense of P–O–P bonds. All the glasses were found to dissolve congruently and in a controlled manner. Finally, the antimicrobial properties of the copper-doped glasses were examined and compared to bioactive glasses which are known to exhibit good antimicrobial properties. The CuO addition leads to higher antimicrobial properties than the commercial bioactive glass S53P4 and total bacterial elimination could be obtained.     

A novel route for synthesis, characterization of molybdenum diselenide thin films and their photovoltaic applications

Molybdenum diselenide thin films were deposited by chemical method. The precursor solution contains ammonium molybdate, sodium selenosulphite with hydrazine hydrate as a reducing agent. Various preparative conditions were optimized for the formation of thin films. The X-ray diffraction pattern shows that thin films have a layer-hexagonal phase. EDAX analysis shows that the films are nearly stoichiometric of Mo: Se: 1:2. Optical properties show a direct band gap nature with band gap energy 1.43 eV and having specific electrical conductivity in the order of 10^?5 (Ωcm)^?1. The configuration of fabricated cell is n-MoSe₂ | NaI (2 M) + I₂ (1 M) | C (graphite). The photoelectrochemical characterization of the films is carried out by studying current–voltage characterization, capacitance–voltage and power output characteristics. The fill factor and efficiency of the cell were found to be 34.22 and 1.01 % respectively.     

SnO2 films prepared by activated reactive evaporation

Transparent conducting films of SnO₂ doped with antimony were prepared on glass substrates by activated reactive evaporation for the first time. The sheet resistance and optical transmittance in the wavelength range 0.4–1.6 μm were studied as functions of various deposition parameters such as the ambient pressure of an 85%Ar15%O₂ mixture, the substrate temperature and the antimony doping concentration in the SnSb alloys. The sheet resistance and optical transmittance showed a strong dependence on the above-mentioned deposition parameters. The best results were obtained for a 90at.%Sn10at.%Sb alloy evaporated in 85%Ar15%O₂ at a partial pressure of about 5 × 10^?4 Torr with a substrate temperature about 350°C. These films, with a sheet resistance of 10 μ/□ had an average transmittance of 95% over the wavelength range 0.4–1.8 μm. The film thickness was about 0.25 μm. Thicker films (about 0.5 μm) had a sheet resistance as low as 1.5 ω/□ with an average transmittance 85% in the wavelength range 0.4–1.6 μm.     

Fabrication of Cu2ZnSnS4 absorber layers with adjustable Zn/Sn and Cu/Zn+Sn ratios

In this work Cu₂ZnSnS₄ (CZTS) thin films were successfully prepared by sulfurization of spin coated CuO + ZnO precursor films under Sn and S ambience with different time. Precursor films were synthesized using air-stable inks consist of carboxylate-capped metal oxide nanoparticles. The composition, microstructure and properties of CZTS thin films prepared with different sulfurization time were investigated using inductively coupled plasma-mass spectrometry, X-ray diffraction, scanning electron microscopy, Raman spectroscopy and UV–vis–NIR spectroscopy. The inductively coupled plasma-mass spectrometry results show that mole ratios of Zn/Sn and Cu/(Zn + Sn) in the films can be adjusted by controlling sulfurization time. A composition of Cu/Zn + Sn = ~0.8, and Zn/Sn = ~1.2 can be reached after sulfurizating with proper time. The influence of element composition change was also studied in our work using X-ray diffraction and Raman scattering. Two laser sources of 325 and 514 nm were involved in the Raman scattering analyze in order to identify secondary phases such as ZnS and Cu_2?xS. The as-prepared CZTS films with a composition of Cu/Zn + Sn = ~0.8, and Zn/Sn = ~1.2 exhibit a direct optical band gap about 1.45 eV.     

The synthesis and characterization of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin films from melt reactions using xanthate precursors

Kesterite, Cu₂ZnSnS₄ (CZTS), is a promising absorber layer for use in photovoltaic cells. We report the use of copper, zinc and tin xanthates in melt reactions to produce Cu₂ZnSnS₄ (CZTS) thin films. The phase of the as-produced CZTS is dependent on decomposition temperature. X-ray diffraction patterns and Raman spectra show that films annealed between 375 and 475 °C are tetragonal, while at temperatures <375 °C hexagonal material was obtained. The electrical parameters of the CZTS films have also been determined. The conduction of all films was p-type, while the other parameters differ for the hexagonal and tetragonal materials: resistivity (27.1 vs 1.23 Ω cm), carrier concentration (2.65 × 10⁺¹⁵ vs 4.55 × 10⁺¹⁷ cm^?3) and mobility (87.1 vs 11.1 cm² V^?1 s^?1). The Hall coefficients were 2.36 × 10³ versus 13.7 cm³ C^?1.     

Oxidation potential control of VO2 thin films by metal oxide co-sputtering

For metal-to-insulator transition (MIT) in vanadium oxide thin film, a thermodynamically stable vanadium dioxide (VO₂) phase is essential. In VO₂ films sputter-deposited on a quartz substrate from a V₂O₅ target, a radio-frequency (RF) magnetron sputter system at working pressure of 7 mTorr is used. Due to the lower sputtering yield of oxygen compared to vanadium leading to oxygen-ion deficiency, the reduction of V ions is resulted to compensate charge with the oxygen ions. Under lower working pressures, the deposition rate increases, but a simultaneous oxygen-ion deficiency causes the destabilization of VO₂. To prevent this, titanium oxide co-deposition is suggested to enrich the oxygen source. When TiO₂ is used, it is found that the Ti ion has a stable +4 charge state so that the use of extra oxygen in sputtering prevents the destabilization of VO₂. However, this is not the case for TiO. For the latter, Ti ions are oxidized from the +2 state to the +3 and +4 states, and V ions with less oxidation potential are reduced to +3 or so. Pure VO₂ thin film exhibits MIT at 66 °C and a large resistivity ratio of four orders of magnitude from 30 to 90 °C. The (V₂O₅ + TiO₂) system under working pressure as low as 5 mTorr yields fairly good films comparable to pure VO₂ deposited at 7 mTorr, whereas the use of TiO yields films with MIT absent or considerably weakened.     

Adhesion enhancements and internal stress in MgF2 films deposited with ion beam assistance

We performed adhesion measurements using a dynamically loaded scratch tester to evaluate MgF₂ coatings deposited onto heated and unheated fused silica substrates. Resistance evaporation at 5 Å s^-1 with Ar⁺ ion beam assistance improved the relative adhesive strength of films deposited onto unheated substrates by over an order of magnitude compared with the results for heated substrates without ion beam assistance. Additional experiments were performed to measure internal stress in MgF₂ films on specially masked BK-7 glass substrates using modulated transmission ellipsometry. We found that ion-assisted deposition can reduce internal stress to approximately 450 kgf cm^-2 (tensile) in films 2300 Å thick. The great potential for stress relaxation in MgF₂ films deposited with ion assistance is suggested by these measurements, but additional work with films of higher purity may be required to identify the relative contributions of stress relief, substrate cleaning and chemical bonding to improved adhesion.     

Fast response time alcohol gas sensor using nanocrystalline F-doped SnO2 films derived via sol–gel method

Pure and fluorine-modified tin oxide (SnO₂) thin films (250–300 nm) were uniformly deposited on corning glass substrate using sol–gel technique to fabricate SnO₂-based resistive sensors for ethanol detection. The characteristic properties of the multicoatings have been investigated, including their electrical conductivity and optical transparency in visible IR range. Pure SnO₂ films exhibited a visible transmission of 90% compared with F-doped films (80% for low doping and 60% for high doping). F-doped SnO₂ films exhibited lower resistivity (0· 12 × 10^???4 Ω  cm) compared with the pure (14·16 × 10^???4 Ω  cm) one. X-ray diffraction and scanning electron microscopy techniques were used to analyse the structure and surface morphology of the prepared films. Resistance change was studied at different temperatures (523–623 K) with metallic contacts of silver in air and in presence of different ethanol vapour concentrations. Comparative gas-sensing results revealed that the prepared F-doped SnO₂ sensor exhibited the lowest response and recovery times of 10 and 13 s, respectively whereas that of pure SnO₂ gas sensor, 32 and 65 s, respectively. The maximum sensitivities of both gas sensors were obtained at 623 K.     

Effect of annealing time on the structural,optical and electrical characteristics of DC sputtered ITO thin films

Using an Indium tin oxide (ITO) ceramic target (In₂O₃:SnO₂, 90:10 wt%), ITO thin films were deposited by conventional direct current magnetron sputtering technique onto glass substrates at room temperature. The obtained ITO films were annealed at 400 °C for different annealing times (1, 2, 5, 7, and 9 h). The effect of annealing time on their structural, optical and electrical properties was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microcopy (AFM), ultra violet–visible (UV–Vis) spectrometer, and temperature dependence Hall measurements. XRD data of obtained ITO films reveal that the films were polycrystalline with cubic structure and exhibit (222), (400) and (440) crystallographic planes of In₂O₃. AFM and Scanning Electron Microscopy SEM have been used to probe the surface roughness and the morphology of the films. The refractive index (n), thickness and porosity (%) of the films were evaluated from transmittance spectra obtained in the range 350–700 nm by UV–Vis. The optical band gap of ITO film was found to be varying from 3.35 to 3.47 eV with the annealing time. The annealing time dependence of resistivity, carrier concentration, carrier mobility, sheet resistance, and figure of merit values of the films at room temperature were discussed. The carrier concentration of the films increased from 1.21 × 10²⁰ to 1.90 × 10²⁰ cm^?3, the Hall mobility increased from 11.38 to 18 cm² V^?1 s^?1 and electrical resistivity decreased from 3.97 × 10^?3 to 2.13 × 10^?3 Ω cm with the increase of annealing time from 1 to 9 h. Additionally, the temperature dependence of the carrier concentration, and carrier mobility for the as-deposited and 400 °C annealed ITO films for 2 and 9 h were analysed in the temperature range of 80–350 K.     

Structural and wettability investigation of titanium dioxide coating: influence of dopant concentration (Si and Sr)

In this study, different samples of Si and Sr co-doped TiO₂ thin films (5 mol% Si and 5-10-15-20 mol% Sr) were prepared via simple sol–gel synthesis method by using strontium acetate as strontium precursor, tetraethoxysilane as silicon precursor, and titanium (IV) isopropoxide (TTIP) as titanium precursor. The effects of co-doping process on the structural, optical, and wettability properties of thin films were studied by X-ray diffraction (XRD), Scanning electron microscope (SEM) and contact angle measurement. XRD results showed that, the anatase phase formation was promoted by Si⁺⁴ and Sr⁺² co-doped TiO₂ samples at higher percentage of Sr.Accordingly, the titania thin films showed various water contact angles, the water contact angles first decreased from 55.1° to 8.1° then increased to 40.7° by changing the content of Sr dopant from 5 to15 mol% and then to 20% mol.     

The variation of the features of SnO2 and SnO2:F thin films as a function of V dopant

V doped SnO₂ and SnO₂:F thin films were successfully deposited on glass substrates at 500 °C with spray pyrolysis. It was observed that all films had SnO₂ tetragonal rutile structure and the preferential orientation depended on spray solution chemistry (doping element and solvent type) by X-ray diffraction measurements. The lowest sheet resistance and the highest optical band gap, figure of merit, infrared (IR) reflectivity values of V doped SnO₂ for ethanol and propane-2-ol solvents and V doped SnO₂:F films were found to be 88.62 Ω–3.947 eV–1.02 × 10^?4 Ω^?1–65.49 %, 65.35 Ω–3.955 eV–8.54 × 10^?4 Ω^?1–72.58 %, 5.15 Ω–4.076 eV–6.15 × 10^?2 Ω^?1–97.32 %, respectively, with the electrical and optical measurements. Morphological properties of the films were investigated by atomic force microscope and scanning electron microscope measurements. From these analysis, the films consisted of nanoparticles and the film morphology depended on doping ratio/type and solvent type. It was observed pyramidal, polyhedron, needle-shaped and spherical grains on the films’ surfaces. The films obtained in present study with these properties can be used as front contact for solar cells and it can be also one of appealing materials for other optoelectronic and IR coating applications.     

Use of Sodium Lactate and Modified Atmosphere Packaging for Extending the Shelf Life of Ready‐to‐Cook Fresh Meal

In this work, the combined effects of sodium lactate and modified atmosphere packaging (MAP) in extending the shelf life of a ready‐to‐cook fresh skewer, made up of raw pork chops and semi‐dried vegetable mix (i.e. zucchini, peppers and tomatoes), were investigated. In the first experimental step, a sodium lactate solution was used to dip pork chops at three different concentrations: 20, 40 and 60% w/w. The second part of the work was focused on the use of MAP. In particular, the following MAPs were tested: MA1 (50%O₂/30%CO₂/20%N₂), MA2 (70%O₂/30%CO₂), MA3 (30%O₂/70%CO₂) and MA4 (30%O₂/30%CO₂/40%N₂). Finally, the optimal concentration of sodium lactate and the best gas composition were combined. The samples were stored at 4 °C; their microbial and sensory qualities were monitored along the entire observation period. The results indicate that the shelf life of the investigated ready‐to‐cook meal can be extended by approximately 83%, if compared with the control skewer packaged in air. The best preservation strategy is the combination of dipping of meat pieces in 40% sodium lactate solution and packaging under MA1. Copyright © 2014 John Wiley & Sons, Ltd.     

Structural,morphological and optical properties of undoped and Co-doped ZnO thin films prepared by sol–gel process

Undoped and Co-doped ZnO thin films with different amounts of Co have been deposited onto glass substrates by sol–gel spin coating method. Zinc acetate dihydrate, cobalt acetate tetrahydrate, isopropanol and monoethanolamine (MEA) were used as a precursor, doping source, solvent and stabilizer, respectively. The molar ratio of MEA to metal ions was maintained at 1.0 and a concentration of metal ions is 0.6 mol L^?1. The Co dopant level was defined by the Co/(Co + Zn) ratio it varied from 0 to 7 % mol. The structure, morphology and optical properties of the thin films thus obtained were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis), photoluminescence (PL) and Raman. The XRD results showed that all films crystallized under hexagonal wurtzite structure and presented a preferential orientation along the c-axis with the maximum crystallite size was found is 23.5 nm for undoped film. The results of SEM indicate that the undoped ZnO thin film has smooth and uniform surface with small ZnO grains, and the doped ZnO films shows irregular fiber-like stripes and wrinkle network structure. The average transmittance of all films is about 72–97 % in the visible range and the band gap energy decreased from 3.28 to 3.02 eV with increase of Co concentration. DRX, EDX and optical transmission confirm the substitution of Co²⁺ for Zn²⁺ at the tetrahedral sites of ZnO. In addition to the vibrational modes from ZnO, the Raman spectra show prominent mode representative of Zn_yCo_3?yO₄ secondary phase at larger values of Co concentration. PL of the films showed a UV and defect related visible emissions like violet, blue and green, and indicated that cobalt doping resulted in red shifting of UV emission and the reduction in the UV and visible emissions intensity.