La-doped ZnO Research Articles

Enhanced optoelectronic characteristics of La-doped ZnO and its compatibility with Cs-doped MAPbI3 perovskite absorber material

Abstract The present study investigates the structural, electrical and optical characteristics of pristine and lanthanum (La)-doped zinc oxide electron transport layers (ETLs) fabricated by the sol gel method and their compatibility with Cs0.10MA0.90Pb(I0.9Br0.10)3 absorber layer for perovskite solar cells. All the ETLs were deposited under same deposition conditions, with the only difference in La percentage in the precursor solutions, ranging from 0 to 6%. X-ray diffraction (XRD) analysis demonstrated the presence of crystalline ZnO thin films and the absence of any impurity phases after La-doping. The calculated crystallite size, determined using Scherrer’s equation, increased from 11.13 to 21.76 nm after the introduction of dopant. The doping with 4% La led to the decrease in the optical bandgap from 3.32 eV of pristine ZnO to 3.23 eV. SEM analysis revealed better morphology of perovskite/4% La:ZnO specimen, which facilitated the absorbance and reduced the charge carrier recombination. It also exhibited superior resilience towards moisture and humidity which will eventually contribute to the development of more stable and efficient planar perovskite solar cells (PCSs).

Physical properties of La-doped ZnO thin films prepared by spray pyrolysis technique

In this research, La-doped ZnO thin films were produced using the spray pyrolysis method to study the influence of La concentration. The films were doped with La at different concentrations ranging from 1 to 5 weight percent (wt%). Various physical properties of the deposited films were examined using a variety of techniques. X-ray diffraction analysis indicated the presence of a hexagonal ZnO phase as the only crystalline phase in all deposited films. The crystallite size was calculated using Scherrer’s equation. Field emission scanning electron microscopy (FE-SEM) images revealed the formation of large grains exceeding the crystallite size, with the smallest grain size of 143.5 nm observed in the La-1 wt% film. Energy dispersive x-ray (EDX) analysis confirmed the existence of La in the deposited films. The optical band gap values were found to increase from 2.7 to 3.3 eV with increasing La content. Notably, a significant decrease in decay time was noted in UV sensing performance at La concentrations of 3 and 5 wt%.

Chemical precursor-dependent dual effect of doping on the gas-sensing performance of metal oxide semiconducting materials

In this study, we report a chemical precursor-dependent dual effect of doping on the gas-sensing performance of metal oxide semiconducting materials. Our findings challenge the conventional notion that optimal doping consistently enhances gas-sensing properties. Acetate and nitrate salts were used as chemical precursors, lanthanum (La) was used as a dopant, and ZnO was used as a semiconducting material. All materials were synthesized under identical conditions by a two-step process involving dip coating and hydrothermal methods. Gas-sensing results demonstrated an improvement in the performance of the acetate-based doped film and a decline in that of the nitrate-based doped film compared to their respective pure counterparts. Among the produced sensors, 1 wt% La-doped ZnO sensor produced by the acetate precursor proved to be convenient for usages in real markets. It showed superior performance with a high response (62) at a relatively low operating temperature (150℃) towards 50 ppm of NH3 gas. The sensor also demonstrated exceptional baseline stability, high short-term and long-term consistency, good selectivity, and strong tolerance to humidity (up to 70 RH%) with slightly slow adsorption-desorption rates. The dual effect was discussed with respect to dopant- and precursor-induced variations in structural and surficial characteristics, revealed by XRD, Raman, FESEM, AFM, and XPS. The discussion delved deeper into the role of chemical precursors on nanostructure growth and, for the first time, illuminated a temperature-dependent complex gas-sensing principle governed by the detected p-n shift of the semiconductor type of the sensing elements, confirmed by Hall effect.

Ultrasensitive and selective detection of ammonia gas at room temperature of La-doped ZnO thin films

Ultrasensitive and selective detection of ammonia gas at room temperature of La-doped ZnO thin films

Synergistic effects of La-doping on ZnO nanostructured photocatalysts for enhanced MB dye degradation

In this work, we present the design and characterization of pristine and La-doped ZnO photocatalysts, prepared via a facile co-precipitation technique. A comprehensive range of characterization techniques was employed to analyze the physicochemical properties of these synthesized nanostructured photocatalysts. The slight shift in the position of peaks in the X-ray diffraction (XRD) pattern confirms successful doping (La3+) of ZnO. Additionally, the identified wurtzite phase further validates the presence of ZnO nanostructures. Subsequent photocatalytic investigations were conducted using model solutions of water and methylene blue (MB) dyes under solar irradiation, meticulously comparing the performance of pure ZnO with La3+ doped ZnO. Over the time span of 90 min, the 5 % La-doped ZnO photocatalysts exhibited an impressive 98 % degradation efficiency for MB dye, surpassing the performance of the pristine ZnO counterpart (0 % La), which achieved only 51 % degradation. This emphasizes the pronounced enhancement resulting from the incorporation of La ions. The photoluminescence (PL) spectra insights with 5 % La3+doping exhibit significant quenching, caused by the suppression of charge carrier recombination, which enhances the photocatalyst's charge transport. X-ray photoelectron spectroscopy (XPS) spectra provided crucial insights into the elemental composition and chemical states of the 5 % La3+ doped ZnO nanostructures. Through systematic reusability assessments, it was established that the 5 % La-doped ZnO photocatalysts maintain their efficiency for up to four cycles, without displaying a significant reduction in removal efficacy. This emphasizes the inherent reliability and robustness of the developed photocatalysts.

High response chemiresistive room temperature ammonia gas sensor based on La-doped ZnO samples

The current study describes the excellent sensing properties of zinc oxide samples with varying La doping concentrations (1, 3, and 5 %). The X-ray diffraction (XRD) study suggests that the produced ZnO samples exhibit hexagonal structure. Due to varying concentrations of La, a notable difference in the morphological image of the samples was observed using a Field Emission Scanning Electron Microscope (FESEM). The existence of La, Zn, and O elements in the sample was analyzed by Energy Dispersive X-Ray Analysis (EDX). The Fourier Transform Infrared Spectroscopy (FTIR) studies validate the sample's structure and functional group. The UV–Vis results showed that the maximum optical reflectance of 90 % was attained in the visible region and the obtained band gap values for the samples were in the range of 3.27–3.33 eV. At ambient temperature, the La-doped samples demonstrated high sensitivity towards ammonia (NH3) and had the highest response value of 1940 % for the 250 ppm. According to the results, an excellent operating stability, and response/recovery time were obtained for the ZnO:La1% sample which suggests that the sample can serve as the most appropriate metal oxide for the detection of NH3 at room temperature.

Experimental and ab initio studies of enhance photocatalytic efficiency of La-doped ZnO/g-C3N4 nanocomposites for bromothymol blue dye degradation

The ability of photocatalysis to clean up environmental contamination, notably in the treatment of water and air, has received extensive research. The composite materials synthesized by the coprecipitation method were made of ZnO and graphitic carbon nitride (g-C3N4) with various concentrations of lanthanum doping (La-ZnO). It was discovered that La metal ions were evenly distributed throughout the layered stacking structures of ZnO nanosheet, which had an impact on the band structure and increased the rate of electron-hole separation and visible light absorption. First-principles calculations show that La-doped ZnO-gC3N4 possesses a direct band gap and a type-II band structure with the conduction band minimum and the valence band maximum located in separate layers. A built-in electric field from the gC3N4 to the La-doped ZnO has been established through an analysis of charge density difference, Bader charge, work function, and band alignment. The electron-hole pair becomes spatially separated as a result, which increases the photodegradation activity. High interfacial charge transfer, efficient charge separation and migration, and high visible light optical absorbance were caused by the direct coating of ZnO on an ultra-thin g-C3N4 layer. The 0.6 % La-doped ZnO-gC3N4 degraded 97 % of the bromothymol blue (BB) dye, which was four times higher than the bulk ZnO, which could remove only about 21 % of the dye at the same time. The combined effects of lower photo corrosion, higher solar light usage owing to a hollow structure and heterostructured semiconductor photocatalysis contribute to this increased photocatalytic activity. The capacity of La-doped ZnO/g-C3N4 nanocomposite to effectively break down BB dye via photocatalysis suggests that it has the potential to address the problems associated with dye pollution in water systems.

Unraveling the Complex Interactions: Machine Learning Approaches to Predict Bacterial Survival against ZnO and Lanthanum-Doped ZnO Nanoparticles.

The rise in antibiotic-resistant bacteria is a global health challenge. Due to their unique properties, metal oxide nanoparticles show promise in addressing this issue. However, optimizing these properties requires a deep understanding of complex interactions. This study incorporated data-driven machine learning to predict bacterial survival against lanthanum-doped ZnO nanoparticles. The effect of incorporation of lanthanum ions on ZnO was analyzed. Even with high lanthanum concentration, no significant variations in structural, morphological, and optical properties were observed. The antibacterial activity of La-doped ZnO nanoparticles against Gram-positive and Gram-negative bacteria was qualitatively and quantitatively evaluated. Nanoparticles induce 60%, 95%, and 55% bacterial death against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, respectively. Algorithms such as Multilayer Perceptron, K-Nearest Neighbors, Gradient Boosting, and Extremely Random Trees were used to predict the bacterial survival percentage. Extremely Random Trees performed the best among these models with 95.08% accuracy. A feature relevance analysis extracted the most significant attributes to predict the bacterial survival percentage. Lanthanum content and particle size were irrelevant, despite what can be assumed. This approach offers a promising avenue for developing effective and tailored strategies to reduce the time and cost of developing antimicrobial nanoparticles.

Advanced NH3 Detection by 1D Nanostructured La:ZnO Sensors with Novel Intrinsic p-n Shifting and Ultrahigh Baseline Stability.

Due to its stability, transportability, and ability to be produced using renewable energy sources, NH3 has become an attractive option for hydrogen production and storage. Detecting NH3 is then essential, being a toxic and flammable gas that can pose dangers if not properly monitored. ZnO chemiresistive sensors have shown great potential in real NH3 monitoring applications; yet, research and development in this area are ongoing due to reported limitations, like baseline instabilities and sensitivity to environmental factors, including temperature, humidity, and interferent gases. Herein, we suggest an approach to obtain sensors with competitive performance based on ZnO semiconducting metal oxides. For this purpose, one-dimensional nanostructured pure and La-doped ZnO films were synthesized hydrothermally. Incorporating large rare earth ions, like La, into the bulk lattice of ZnO is challenging and can lead to surface defects that are influential in gas-sensing reactions. The sensors experienced a temperature-induced p-n shifting at about 100 °C, verified by the Hall effect and AC impedance measurements. The doped sensor showed exceptional stepwise baseline stability and outstanding performance at a relatively low operating temperature (150 °C) with a sensing response of 91 at best (@ 50 ppm NH3) and recorded a tolerance to water vapor up to 70% RH. Alongside p-n shifting, the enhanced performance was discussed in correlation with La doping-triggered changes in the nanostructural and surfacial properties of the films. We validated the proposed technique by producing similar sensors and performing multiple replicates to ensure consistency and reproducibility. We also introduced the fill factor concept into the gas sensor field as a new trustworthy parameter that could improve sensor performance assessment and help rate sensors based on deviation from ideality.

Synergetic Improvement of the Reactive Performance of Hydrogen Sulfide Adsorption on a Three-Dimensional Ordered Macroporous La-Doped ZnO Sorbent

Synergetic Improvement of the Reactive Performance of Hydrogen Sulfide Adsorption on a Three-Dimensional Ordered Macroporous La-Doped ZnO Sorbent

Highly sensitive and selective acetone gas sensor-based La-doped ZnO nanostructured thin film

In the present study, the spray pyrolysis technique is used to synthesize pure and La-doped ZnO nanostructured thin films. The prepared films were characterized structurally, optically, and morphologically. The sensor showed a highly selective nature towards acetone gas. The prepared La-doped ZnO sensor showed an increased response of 82.57 % for 50 ppm of acetone gas operating at 150 oC with faster response and recovery times of 26 s and 27 s, respectively. The resulting sensing performances were found to be reproducible with no evidence of ageing. The observed exceptional gas sensing performance was attributed to the higher surface-to-volume ratio, increased surface defects, and morphology. This work provides insight into fabricating the acetone gas sensor operating at lower temperatures.

Fabrication of high-performance RT-NH3 gas sensor based on Cu and La co-doped ZnO films through a facile drop-casting method

In this work, undoped ZnO, 2 % Cu-doped ZnO, 2 % La-doped ZnO and 2 % (Cu:La) co-doped ZnO thin films are deposited on glass substrates using the facile drop-casting method, and their physical characteristics were investigated for the gas sensing application. The X-ray diffraction (XRD) patterns confirmed the hexagonal wurtzite structure and increase in crystallinity for the doped samples. Field Emission Scanning Electron Microscopy (FESEM) images revealed a significant change in morphology from the granular particles to densely packed nanoplates-like morphology for (Cu:La) co-doped ZnO. The doped samples exhibited a red shift in absorption edge and shrinkage of the optical bandgap. Multiple emission peaks in photoluminescence (PL) spectra indicated the presence of defect level in the material. It was discovered that Cu-doped and La-doped ZnO thin films had a considerable NH3 sensing response at ambient temperature. The gas response was remarkably enhanced to 341 % for (Cu:La) co-doped ZnO film and a quicker response/recovery time of 80/10 s for 250 ppm NH3. The (Cu:La) co-doped ZnO can serve as a feasible alternative for pure ZnO gas sensors.

STRUCTURE, OPTICAL PROPERTIES AND PHOTOCATALYTIC ACTIVIYY OF UNDOPED, La2O3-DOPED ZnO NANOCOMPOSITES

La-doped ZnO nanocomposites with di­ffe­rent content of La2O3 (1–5%) were obtained by the Pechini method from their nitrate solutions. The solutions of Zn2+ and La3+ nitrates were preliminary obtained by dissolving of zinc and lanthanum oxides with a content of the main component of 99.99% in nitric acid. The influence of lanthanum doping the on the microstructure, morphology, optical pro­perties and photocatalytic activity of the ZnO nanopowders were examined. The properties of the nanopowders were studied by using X-ray phase analysis, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy. The samples were subjected to X-ray powder diffraction using a DRON-3 diffractometer (Cu-K radiation) at room temperature. The scan angle was 0.05–0.1 ° in the range 2 = 15–90 °. X-ray phase ana­lysis confirms the formation of single phase of La2O3-doped ZnO powders on diffractograms. Raman light scattering and photoluminescence spectra were recorded using a Horiba Jobin‑Yvon T64000 spectrometer equipped with a CCD detector at room temperature in the inverse scattering geometry. According to SEM results, the powders characterized a conglomerate structure. The undoped ZnO has an average particle size of 43 nm, while the average particle size of La3+-doped ZnO ranges from 64 to 80 nm. It was established that the morphology of powder particles primarily depends on the content of La3+ in the material. An increase in the amount of La3+ in zinc oxide leads to an increase in the specific surface area (from 3.8 to 11.8 m2/g). In the photoluminescence spectra of ZnO powders, with increasing La2O3 concentration, bands at 400 nm are observed due to the appearance of impurities that cause of interstitial zinc and zinc vacancy defects and their broade­ning with a shift to the long-wave region. Photocatalytic properties of ZnO pow­ders doped with lanthanum oxide were in­vestigated using Methyl Orange as a model dye under Osram Ultra-Vitalux lamp (300 W) irradiation. A present result indicates that the obtained powders are potential candidate for the practical application in photocatalysis.

Design of high-sensitivity La-doped ZnO sensors for CO2 gas detection at room temperature

For the sake of people's health and the safety of the environment, more efforts should be directed towards the fabrication of gas sensors that can operate effectively at room temperature (RT). In this context, increased attention has been paid to developing gas sensors based on rare-earth (RE)-doped transparent conducting oxides (TCO). In this report, lanthanum-doped zinc oxide (La-doped ZnO) films were fabricated by sol–gel and spin-coating techniques. XRD analysis revealed the hexagonal structure of the ZnO films, with preferred growth along the (002) direction. The crystallite size was decreased from 33.21 to 26.41 nm with increasing La content to 4.0 at.%. The UV–vis–NIR indicating that the films are highly transparent (˃ 80%), La-doping increased the UV blocking ability of the films and narrowed the optical band gap (Eg) from 3.275 to 3.125 eV. Additionally, La-doping has influenced the refractive index of the samples. Gas sensing measurements were performed at ambient temperature (30 °C) and a relative humidity (RH) of 30%, employing different flow rates of carbon dioxide (CO2) gas used synthetically with air. Among the evaluated sensors, the ZnO: 4.0 at.% La sensor exhibited the most significant gas response, with a value of 114.22%. This response was observed when the sensor was subjected to a flow rate of 200 SCCM of CO2 gas. Additionally, the sensor revealed a response time of 24.4 s and a recovery time of 44 s. The exceptional performance exhibited by the sensor makes it very appropriate for a wide range of industrial applications. Additionally, we assessed the effect of humidity, selectivity, reusability, repeatability, detection limit, and limit of quantification.

Nanotubes/nanorods-like structures of La-doped ZnO for degradation of Methylene Blue and Ciprofloxacin

In this study, nanotubes/nanorods-like structures of Zn0.97La0.03O compound were synthesized at different pH values (pH = 8, 9, 10, 11, and 12), and the photocatalytic response for Methylene Blue (MB) dye and Ciprofloxacin (CIP) drug were investigated. It was verified that the pH variation directly impacts the ZnO crystal structure, morphology, optical and photocatalytic properties. The basic and alkaline pH values cause a decrease in the crystallite size and these differences may have contributed to the band gap energy values variations. Oxygen vacancy defects (VO, VO+, and VO++) were abundant in the La-doped ZnO samples, which also demonstrated to be formed from mesopores, as seen in N2 adsorption/desorption results. The photocatalytic response of the materials was verified in MB and CIP solutions under UV irradiation conditions. The sample synthesized at pH 9 (ZL9) demonstrated greater capacity to remove MB (91.45 %) and CIP (87.6 %) in typical pseudo-first-order kinetics. Using different inhibitors, it was observed that the •OH radicals were the species involved in the photocatalysis of pollutants for the ZL9 sample. In addition, this material demonstrated a satisfactory ability to remove pollutants even after three consecutive uses. This study demonstrates that pH is an important parameter to consider in the synthesis process of ZnO nanostructures, directly influencing the structural, optical, and morphological properties and the degradation of highly dangerous dyes and drugs.

ZnO and La-doped ZnO films by USP method and their characterizations for ultraviolet photodetectors and photocatalysis applications

In this study, ZnO, Zn1-xLaxO [2, 5, 10, 15 at.%] thin films were grown on glass substrates using the spray-pyrolysis technique, to investigate the effect of doping on the structural, morphological, thermoelectric and optical properties of the layers, Also the samples were tested as UV photodetectors and photocatalyst for MB degradation. Firstly, diffraction patterns showed a hexagonal structure, with preferential grain orientation along the (002) direction, for pure ZnO and 2%La_ZnO layers, and at 5 at.% the preferential orientation changes, and crystallite sizes range from 10 nm to 19 nm. However, SEM images reveal that the ZnO and 2%La_ZnO layers are nanorods distributed over their surfaces, and the other 5%LZO, 10%LZO and 15%LZO layers characterized by nanocrystals were hexagonal prisms. The UV–visible analysis of the prepared layers shows high transparency (80–90%) in the visible range, with a constant optical gap of 3.26 eV. Thermoelectric measurements show that the ZnO and LZO layers are non-degenerate, with a maximum charge concentration of 9.18 × 1017 cm−3 for the 15% LZO films. The thin films show an ability for UV detection, while the 5%La_ZnO layers remain the best for UV photodetection with a good sensitivity (5.07) compared with the other layers. In terms of methyl blue degradation, the 5%La_ZnO thin films had a better degradation of 95%.

A UV detector in humid environment by La-doped ZnO NWs array

A UV detector in humid environment by La-doped ZnO NWs array

Study of La Doping on the Electronic Structure and Magneto-Optical Properties of ZnO by GGA+U Method

Based on the density functional theory, the effect of rare-earth La doping at different concentrations on the electronic structure, optical properties, and magnetic properties of ZnO was calculated by using the GGA+U method under the condition of spin polarization. The calculation results show that the cell of a La-doped ZnO system is distorted, resulting in a formation energy less than zero, in which case it is easy to dope. After La doping, the band gap narrows, the Fermi level enters the conduction band, and the excess carriers induced by La atoms degenerate to form n-type degenerate semiconductor materials. In the visible light region, a blue shift in the optical absorption edge of the La-doped ZnO system causes an increased average static dielectric constant, stronger polarization ability, stronger binding ability on charges, and the photoconductivity of the doped ZnO system is improved. The magnetic moment of the La-doped ZnO system is zero, so it is not magnetic.

Highly Efficient Photocatalytic Properties of La-Doped ZnO over Pristine ZnO for Degradation of 2-Chlorophenol from Aquatic Agriculture Waste

Highly Efficient Photocatalytic Properties of La-Doped ZnO over Pristine ZnO for Degradation of 2-Chlorophenol from Aquatic Agriculture Waste

Fabrication of La, Ce co-doped ZnO nanorods for improving photodegradation of methylene blue

La, Ce co-doped ZnO nanorods (ZnLC) were synthesized through a one-step solvothermal route. The photocatalysts were characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, energy dispersive X-ray, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy and photoluminescence spectroscopy. The La and Ce doping enhanced the visible light absorption ability of ZnLC and a red shift was detected for ZnLC. Under simulated solar light irradiation, the ZnO doped with 3 at% La and 1 at% Ce (ZnLC1) degrades methylene blue (MB) more effectively than those of pure ZnO, La-doped ZnO (ZnL) and commercially available ZnO. The improved photocatalytic performance of ZnLC1 can be attributed to the high charge separation efficiency as demonstrated by the photoluminescence spectra. Additionally, the photocatalytic experiments reveal that several parameters have their own impact on the MB degradation. Using a variety of radical scavengers, it is discovered that superoxide anion radical plays a crucial role in the degradation of MB. The ZnLC1 is also reused several times without noticeable decrease of photoactivity, indicating that it has a substantial potential for environmental remediation applications.