Co-doped Zinc Research Articles

Sensitization effect between Ln3+ ions in zinc fluoride glasses for MIR applications

A system of zinc fluoride glasses were synthesized to analyse the sensitization mechanism between doped Ln3+ ions under 808 or 980 nm excitation. Differential scanning calorimetry (DSC) curve and Raman spectra indicate the favourable thermal stability and a low maximum phonon energy of the host. Judd-Ofelt (J-O) theory together with the absorption spectra were utilized to compute the Ωt for predicting radiative features of each sample which coincide with the later measured emission spectra. Broadband emission ranging from 2400 to 3300 nm with a half-width of 361 nm in Er3+/Dy3+ codoped zinc fluoride glasses under 980 nm pumping has been investigated, which may be applicated in mid-infrared fiber amplifier and broadband tunable lasers field. On the other hand, the efficient sensitization effect mechanism between Er3+ and Dy3+ around 3 μm band with an extremely high energy transfer efficiency Ƞ (96.1%) of Er3+:4I13/2→Dy:6H11/2 has been researched under 808 nm excitation. Hence, Er3+ and Dy3+ doped zinc fluoride glasses may be potential optical candidates of great development foreground in the fields of mid-infrared applications.

The synergistically improved afterglow and magnetic resonance imaging induced by Gd3+ doping in ZGGO:Cr3+ nanoparticles

Gd3+ and Cr3+ codoped zinc gallogermanate (ZGGO:Cr3+, Gd3+) nanoparticles were prepared by a hydrothermal method in combination with a subsequent vacuum annealing. It is found that Gd3+ doping not only endows ZGGO:Cr3+ nanoparticles with magnetic property, but also results in the decreased nanoparticle size and the enhanced near infrared (NIR) afterglow intensity. Strikingly, amino group functionalized SiO2 layer coating enabling Gd3+ doped ZGGO:Cr3+ nanoparticles well dispersed in water enhances persistent luminescence which is because of the weakened quenching effect of OH− groups in water. Validation of high-quality bioimaging was demonstrated using the surface functionalized Gd3+ doped ZGGO:Cr3+ nanoparticles dispersed in human serum albumin (HSA). In particular, it is found that the longitudinal relaxivity (7.33 s−1(mM)−1) of Gd3+ doped ZGGO:Cr3+ nanoparticles is higher than that of commercial magnetic resonance imaging (MRI) contrast agent (Gd-DTPA) and it leads to the high-quality in vitro T1-weigthed images.

Facile Green Synthesis of LaCe Co-Doped ZnO Nanoparticles and Their Structural, Optical and Antibacterial Properties

This present work describes the synthesis of LaCe co-doped zinc oxide (ZnO) nanoparticles (NPs) prepared by green method using Gymnema sylvestre (G. sylvestre) leaves as reducing as well as capping agent. Green synthesis method avoids inert gases, high pressure, laser radiation, high temperature, toxic chemicals etc. as compared to conventional method like sol-gel technique method, laser ablation method, solvothermal method, inert gas condensation method and chemical reduction method. The synthesized LaCe co-doped ZnO NPs was characterized by X-Ray diffraction (XRD), field emission scanning electron microscopy (FESEM), elemental analysis (EADX), Fourier transform infrared spectroscopy (FTIR), UV-vis spectroscopy and photoluminescence (PL). The LaCe co-doped ZnO NPs was tested against clinical pathogens such as gram positive G+ (Staphylococcus aureus and Streptococcus pneumoniae) and gram negative G- (Klebsiella pneumoniae, Shigella sydenteriae, Escherichia coli, Pseudomonas aeruginosa and Protus vulgaris) bacterial strains using agar well diffusion method.

A novel electrospun cobalt-doped zinc oxide nanofibers as photoanode for dye-sensitized solar cell

In this article, we developed pure and Cobalt-doped Zinc oxide nanofibers as photoanodes for Dye-sensitized solar cell (DSSC) application. The prepared pure and Co-doped Zinc oxide nanofibers are characterized using Thermo-gravimetric/Differential thermal analysis (TG/DTA), Scanning electron microscope (SEM), Energy-Dispersive x-ray Spectroscopy (EDX) and UV-Vis spectroscopy. The photo-conversion efficiency of the DSSC fabricated with the electrospun pure and Cobalt-doped Zinc oxide nanofibers as photoanodes are found to be highest for 5 wt% Co-doped ZnO nanofibers. It has achieved an enhanced photocurrent density of 5.36 , fill factor of 0.731 and power conversion efficiency of 2.97% under AM 1.5 illumination. The presence cobalt ions in the Zinc oxide nanofibers, obstructs the recombination of the excited electrons with the dye or the electrolyte and thereby enhance with higher efficiency than pure Zinc oxide (η% = 1.63%).

Creation of passivated Nb/N p-n co-doped ZnO nanoparticles and their enhanced photocatalytic performance under visible light illumination

Passivated niobium/nitrogen (Nb-N) p-n co-doped zinc oxide nanoparticles were created by a simple precipitation process with in-situ self-formed NaCl “cage” to confine the nanoparticle growth followed by the heat treatment in a flow of ammonia gas. Enhanced optical absorbance into the visible light region was observed in the Nb/N co-doped ZnO nanoparticle photocatalyst due to the Nb/N co-doping effect. It demonstrated a largely enhanced photocatalytic performance in the disinfection of Escherichia coli bacteria under visible light illumination, which could be attributed to the passivated co-doping of Nb-N to suppress the photogenerated charge carrier recombination on dopants. This robust approach for passivated p-n co-doping may also be applied to other material systems for a wide range of technical applications.

The Effect of RF Power on the Properties of Gallium and Aluminium Co-doped Zinc Oxide (GAZO) Thin Films

X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and spectrophotometry were used to study the effect of RF power on the properties of gallium and aluminium co-doped zinc oxide (GAZO) thin films for optoelectronic device fabrication. Two peaks appeared in the XPS spectra of the Zn 2p core-level at 1045 and 1022 eV, and these were assigned to $${\text{Zn}}~2{{\text{p}}_{1/2}}$$ and $${\text{Zn}}~2{{\text{p}}_{3/2}}$$ , respectively. The O 1s core-level revealed peaks at 530 and 531 eV which indicated the presence of two different forms of oxygen. Raman spectroscopy confirmed the films’ hexagonal wurtzite crystal structure and revealed the presence of few defects and negligible residual tensile stress. Spectral dependence of the refractive index was analyzed on the basis of the Cauchy’s dispersion model and the Wemple and DiDomenico (WDD) single oscillator model. Low refractive indices (1.6–2.0) and nearly zero extinction coefficients were obtained in the visible region (400–700 nm), indicating the high transparency nature of the GAZO thin films. The optical band gap decreased with increasing RF power, in accordance with the Burstein–Moss effect. Low Urbach energy values were obtained at low RF power, indicating less structural disorder. The free carrier concentration to effective mass ratio $$({N_c}{\text{/}}{m^*})$$ , plasma frequency $$({\omega _P})$$ and zero frequency dielectric constant $$({\varepsilon _\infty })$$ were determined. Films deposited at 150 W exhibited the optimum optical properties, desirable for optoelectronic application.

Li and Mg Co-Doped Zinc Oxide Electron Transporting Layer for Highly Efficient Quantum Dot Light-Emitting Diodes.

Zinc-oxide (ZnO) is widely used as an n-type electron transporting layer (ETL) for quantum dot (QD) light-emitting diode (QLED) because various metal doping can be possible and ZnO nanoparticle can be processed at low temperatures. We report here a Li- and Mg-doped ZnO, MLZO, which is used for ETL of highly efficient and long lifetime QLEDs. Co-doping, Mg and Li, in ZnO increases its band gap and electrical resistivity and thus can enhance charge balance in emission layer (EML). It is found also that the O-H concentration at the oxide surface decreases and exciton decay time of QDs on the metal oxide increases by co-doping in ZnO. The inverted green QLEDs with MLZO ETL exhibits the maximum current efficiency (CEmax) of 69.1 cd/A, power efficiency (PEmax) of 73.8 lm/W, and external quantum efficiency (EQEmax) of 18.4%. This is at least two times higher compared with the efficiencies of the QLEDs with Mg-doped ZnO ETL. The optimum Li and Mg concentrations are found to be 10% each. The deep-red, red, light-blue, and deep-blue QLEDs with MLZO ETLs exhibit the CEmax of 6.0, 22.3, 1.9, and 0.5 cd/A, respectively. The MLZO introduced here can be widely used as ETL of highly efficient QLEDs.

Structural, morphological and optical properties of Eu-N co-doped zinc oxide nanoparticles synthesized using co-precipitation technique

The doping of metal oxides with rare-earth element is an effective way of enhancing the optical properties of ZnO nanoparticles. The ZnO nanoparticles were prepared using co-precipitation method with different concentrations of Eu, constant N doping and characterized through X-ray diffraction, scanning electron microscopy, Raman spectroscopy and UV-visible spectroscopy. The Rietveld refined XRD of ZnO nanoparticles confirms the hexagonal wurtzite structure. The XRD results indicated that crystallite size increases with doping and found in the range of 37–52 nm. Scanning electron microscopy illustrated that ZnO nanoparticles were less agglomerated and the average size of nanoparticles was found to increase from 62 to 90 nm with doping. Raman spectrum also confirmed hexagonal wurtzite arrangement of all samples. The band gap of pristine ZnO nanoparticles was found 3.18 eV as confirmed by UV-visible spectroscopy. The red shift (3.14 eV & 3.16 eV) in band gap was observed at 2 & 3 mol% of Eu, while blue shift (3.20 eV & 3.23 eV) in band gap was observed at 1 & 4 mol% of Eu respectively. This modification in the band gap makes ZnO nanoparticles an appropriate electrode material for dye-sensitized solar cells and optoelectronic devices.

Rare earth Eu3+ co-doped AZO thin films prepared by nebulizer spray pyrolysis technique for optoelectronics

Rare earth element (i.e.) europium co-doped aluminum zinc oxide (Eu:AZO) thin films were deposited on microscope glass slides by nebulizer spray pyrolysis with different Eu-doping concentrations (0, 0.5, 1, and 1.5%). The deposited films were investigated using X-ray diffraction, AFM, EDAX, FT-Raman, UV–visible, PL, and Hall effect measurements. X-ray confirmed the incorporation of aluminum and europium ions into the ZnO structure. All films have polycrystalline nature with hexagonal wurtzite structure at (002) direction. Topological depictions exhibited minimum surface roughness and low film thickness for pristine AZO thin film. EDAX study authorizes the existence of Zn, O, Al, and Eu in Eu: AZO thin films. Raman spectra exhibited the characteristic of ZnO-wurtzite structure (E2-high) mode at 447 cm−1. The deposited film showed high optical transmittance of ~90% in visible region, and the direct energy gap was around 3.30 eV for pristine AZO thin film. The PL spectra emitted a powerful UV emission situated at 388 nm, and it indicates that the film has good optical quality. The obtained large carrier concentration and less resistivity values are 4.42 × 1021 cm−3 and 3.95 × 10−4 Ω cm, respectively, for 1.5% Eu-doped AZO thin film. The calculated figure of merit value is 17.29 × 10−3 (Ω/sq)−1, which is more suitable for the optoelectronic device.

Effect of acetic acid and water content in the spray solution on structural, morphological, optical and electrical properties of Al and In co-doped zinc oxide thin films

Aluminium and indium co-doped zinc oxide (AIZO) thin films were deposited using ultrasonic spray pyrolysis. Depositions were performed by varying the acetic acid and water content in the spraying solution which resulted in the formation of different nanostructures like hexagons, flowers, chisels, curved nanostructures, hexagonal pyramids, super grown hexagons, and inter-connected nanostructures. Further, the physical properties such as structural, optical, electrical, and surface texture parameters were examined. The structural studies showed that films were of crystalline nature, with different crystallite sizes and grown with a preferential orientation along (002) plane. The optical transmittance assessments proved that films were highly transparent (> 80%) in the visible region. The electrical sheet resistance was found to be in the range 29–1K Ω/□. Surface parameters like average roughness, root mean square roughness, and peak-valley height values helped to understand the homogeneity of the thin films. Finally, the suitability of AIZO films for transparent conductive oxide applications were tested by estimating the figure of merit (FOM). Among the different solution conditions, films fabricated using a starting solution containing 25 ml of acetic acid and 25 ml of water exhibited the lowest resistivity (2.47 ± 0.03 × 10−3 Ω-cm) along with the highest FOM (5.83 ± 0.42 × 10−3/Ω).

Structural and optical studies on Dy3+:Tb3+ co-doped zinc leadfluoro-borophosphate glasses for white light applications

A new series of Dy3+:Tb3+ co-doped zinc leadfluoro-borophosphate glasses were prepared by varying Tb3+ ions concentration through melt quenching technique. Influence of Tb3+ ions concentration on the structural and spectroscopic properties of Dy3+:Tb3+ co-doped title glasses were explored through FTIR, Raman, optical absorption, luminescence and decay measurements. The phonon vibrational energy of the chosen glass host is found to be 998 cm−1 through Raman spectrum. Dy3+ ions act as sensitizer to Tb3+ ions emission which originates from the 5D4 metastable state of Tb3+ ions through non-radiative energy transfer with a maximum efficiency of 44%. At higher Tb3+ ions concentration, the 4F9/2 metastable state of the Dy3+ ions can also be mutually sensitized by Tb3+ ions which inturn increases the lifetime of the 4F9/2 state of Dy3+ ions. Nature of energy transfer in both the cases was investigated through Dexter's energy transfer mechanism and Inokuti-Hirayama (IH) model. These results suggest that dipole-dipole type of interaction is responsible for Dy3+ to Tb3+ energy transfer and dipole-quadrupole interaction is responsible for Tb3+ to Dy3+ energy transfer. The characteristic emission color of the prepared glasses were examined through CIE 1931 chromaticity coordinates and the corresponding correlated color temperature (CCT) values were estimated which indicates the possible neutral white light emission from the title glasses. All these studies concludes that 0.25 wt% Tb3+ ions co-doped 0.5 wt% Dy3+ ions incorporated titled glass is more suitable for neutral white light emitting applications.

Spectroscopic characterization and temperature-dependent upconversion behavior of Er3+ and Yb3+ co-doped zinc phosphate glass

The zinc phosphate glass co-doped with Er3+ and Yb3+ ions was prepared by melt-quenching method. The Judd-Ofelt theory has been applied to analyze the absorption spectrum and estimate the spectroscopic parameters of Er3+ ions. Upconversion luminescence of the glass was investigated under the excitation at 976 nm. The red and green emissions of Er3+ ions were observed. The energy transfer processes between Yb3+ and Er3+ ions responsible for the upconversion emissions were discussed based on their dependences on pump power. The fluorescence decays of the relevant energy levels were measured for evaluating the energy transfer efficiency. Furthermore, the influence of temperature on upconversion emission in this glass was carried out at temperatures from 323 to 573 K. The result indicates that the glass has a potential application in the construction of optical temperature sensors based on the self-referenced FIR technique.

Structural, Optical and Room Temperature Ferromagnetic Properties of Co-Doped Zinc Oxide Nanorods Prepared by Sol–Gel Method

This study reported the synthesis of cobalt (Co)-doped ZnO nanorods using sol–gel method and characterized their microstructures, morphologies, optical and ferromagnetic properties at room temperature by X-ray diffraction, scanning electron microscopy, ultraviolet-visible absorption spectroscopy, photoluminescence spectrometry and vibrating sample magnetometry. The results revealed that the formation of the hexagonal shaped wurtzite of Co-doped ZnO nanorods for Co content ≤0.01% suggested that Co2+ occupied the sites of Zn2+ ions in the ZnO crystal lattice without forming any secondary phase. Moreover, the optical energy band gap (Eg) of the Co-doped ZnO nanorods decreased with increasing Co concentration, while the absorption band edges were at 565, 610 and 653 nm, corresponding to d–d transition of Co2+ ions in the tetrahedral field of ZnO. Furthermore, the strong Zn interstitials and oxygen vacancy defects induced ferromagnetism in the Co-doped ZnO nanorods with a Tc ≥ 300 K. The optimal values of saturation magnetization (Ms), the remanent magnetization (Mr) and coercive field (Hc) were 1.23 × 10–2 emu/g, 1.7 × 10–3 emu/g and 76 Oe, respectively. These findings suggested that the Co-doped ZnO nanorods exhibited promising attributes for the development of semiconductor devices with excellent ferromagnetic properties at room temperature.

Influence of Co loading on structural and morphological properties of Co-doped ZnO thin films grown by pulsed electron beam ablation

We report on the effect of cobalt loading in the target material on the properties of thin film nanocomposites of Co-doped zinc oxide (CZO) Zn1-xCoxO. The films have been deposited by pulsed electron beam ablation (PEBA) at 450°C on pre-annealed (1100°C) c-sapphire and Si (100) substrates. The experimental results, based on scanning electron and atomic force microscopies (SEM, AFM), indicate that Co doping significantly affects the morphology of the films. X-ray diffraction (XRD) measurements reveal that the films on both substrates exhibit a prominent ZnO hexagonal wurtzite structure for x = 0.05, whereas higher Co loading (x = 0.1, 0.2) results in a strong deformation of ZnO wurtzite lattice and in a higher content of hexagonal close-packed (hcp) metallic Co in CZO films. X-ray photoelectron spectroscopy (XPS) data confirm the presence of non-oxidized metallic Co (Co°) in the deposited films. Both XRD and XPS results indicate an increase in Co° content in the films as Co loading in the target is increased.

Effective sensitization of Eu3+ and energy transfer in Sm3+/Eu3+ co-doped ZPBT glasses for CuPc based solar cell and w-LED applications

Sm3+/Eu3+ co-doped transparent Zinc Phosphate Barium Titanate (ZPBT) glasses have been successfully prepared via melt quenching technique. The photoluminescence properties and energy transfer mechanisms of these glasses were investigated in detail. The addition of Sm3+ as sensitizer expanded the excitation spectrum of Eu3+ in the Sm3+/Eu3+co-doped ZPBT glasses. The mechanism for energy transfer from Sm3+ to Eu3+ was dipole-dipole in nature, which was confirmed by Dexter energy transfer formula and Reisfeld's theory on emission spectra and Inokuti Hirayama (I-H) model on decay curves. The Sm3+/Eu3+ co-doped ZPBT glasses reveal the capability to down-convert the n-UV and blue wavelength photons located in the weakest absorption of copper phthalocyanine (CuPc), to red-emitting photons in the optimal absorption of CuPc. The evaluated CIE chromaticity coordinates for the glasses move towards the red region with the increase in Eu3+ concentration under n-UV excitation wavelength. The above-mentioned results imply that the Sm3+/Eu3+ co-doped ZPBT glasses are the potential candidate for applications in CuPc based solar cells and w-LEDs.

Effect of precursor type and doping concentration on the physical properties of ultrasonically sprayed aluminium and indium co-doped zinc oxide thin films

In this work, we have studied the effect of aluminium dopant precursor type and doping concentration on the structural, morphological, optical and electrical properties of Al and In co-doped zinc oxide (AIZO) thin films deposited by ultrasonic spray pyrolysis. Zinc acetate dihydrate and indium acetate were used as zinc and indium precursors, respectively. Aluminium chloride and aluminium sulphate were used as aluminium precursors. The doping concentrations of Al (1 to 3at%) and In (1 to 3at%), were varied equally and the physical properties were analyzed. X-ray diffraction examinations confirmed that AIZO films were poly crystalline and grown as a hexagonal wurtzite structure. Scanning electron microscopy observations revealed that thin films were grown with different types of hexagonal nanostructures. From the optical and electrical measurements, the figure of merit was estimated. The values were 4.09×10−3/Ω and 0.75×10−3/Ω for the AIZO thin films deposited using aluminium chloride and aluminium sulphate respectively.

Crystal Orientation and Electrical Properties of Al and Ga Co-Doped Zinc Oxide Transparent Conducting Films Deposited on Sapphire Surface

Transparent conducting films of zinc oxide co-doped with aluminum and gallium (AGZO) were deposited on sapphire (single crystal of aluminum oxide) substrates by spray chemical vapor deposition. The AGZO films were epitaxial or with strongly preferred-orientation. The highest mobility was 48 cm2 V-1 s-1 when deposited on r-plane. Deposition on other surfaces doubled the mobility to approximately 30 cm2 V-1 s-1 than that on glass substrate. Resistivity of all films deposited on sapphire substrate were lower than 1.0×10-3 ·cm and lower than that (2.4×10-3 ·cm) deposited on glass substrate. The lowest resistivity was 5.8×10-4 ·cm when deposited on c-plane.

Multicolor and white light emitting Tb3+/Sm3+ co-doped zinc phosphate barium titanate glasses via energy transfer for optoelectronic device applications

A series of Tb3+/Sm3+ co-doped ZPBT glasses have been successfully prepared via melt quenching technique and their photoluminescence properties and energy transfer mechanism were investigated. Tb3+ doped glass exhibits dominant emission peak at 544 nm corresponding to 5D4→7F5 transition under 375 nm excitation whereas Sm3+ doped glass exhibits intense emission peak at 599 nm corresponding to 4G5/2 → 6H7/2 under 399 nm excitation. The CIE chromaticity coordinates (0.259, 0.590) and (0.570, 0.428) are located in the pure green and orange region for Tb3+ and Sm3+ doped glasses, respectively. The Tb3+/Sm3+ co-doped glasses under 375 nm excitation emit a combination of blue, green and orange-red light while under 484 nm excitation emits green and red-orange emission light. The energy transfer occurs from Tb3+ to Sm3+ via dipole-dipole interaction, which was confirmed by applying Dexter and Reisfeld's theory and Inokuti Hirayama (I-H) model. Moreover, the energy transfer efficiencies and probabilities were calculated from the decay curves. The color tone of these glasses can be modulated from yellowish-green to warm-white via greenish-yellow by appropriate tuning of Sm3+ concentrations and excitation wavelengths. These results indicate that the prepared glasses can be a potential candidate for white light as well as solid state lighting applications.

Effect of silver nanoparticles on the upconversion and near-infrared emissions of Er 3+ :Yb 3+ co-doped zinc tellurite glasses

Abstract The effect of the silver nanoparticles on the optical response of the Er 3+ /Yb 3+ co-doped zinc tellurite glasses was studied. The glasses were characterized by optical absorption spectroscopy, transmission electron microscopy and X-ray diffractometry. The characteristic radiative emissions of Er 3+ ions at visible (upconversion) and near-infrared spectral regions were recorded by exciting the samples at 980 nm excitation wavelength. The intensities of upconversion and near-infrared emissions were enhanced up to 180% and 130%, respectively. The increase in luminescence intensity is attributed to the enhanced effective localized field induced by silver nanoparticles. Lifetime measurements were conducted to investigate the presence of energy transfer between Er 3+ and silver.

Single oscillator model of undoped and co-doped ZnO thin films

Undoped and co-doped zinc oxide thin films were deposited on glass substrates using a chemical spray technique. The experimental Lorentz profiles of co-doped ZnO thin films were measured in the spectral region 720–1750nm. A single oscillator model of the resulted materials is constructed by calculation of: zero-frequency refractive index (no), average interband oscillator wavelength (λo), oscillator strength (So), dispersion energy (Ed), single-effective oscillator energy (Eo), plasma oscillation frequency (ωp) and interband transition strength moments (M−1, M−3).