Er-doped SnO2 Research Articles

Optical and nonlinear characterization of Er-doped SnO2 thin films fabricated by thermal evaporation: potential for advanced optical device applications

Optical and nonlinear characterization of Er-doped SnO2 thin films fabricated by thermal evaporation: potential for advanced optical device applications

Rectifying behavior of the GaAs / Er-doped SnO2 heterostructure: Interface dipole role and monochromatic light influence

The characteristic current-voltage (I x V) curves are measured across the interface of a GaAs/SnO2 heterostructure, where the top layer (tin dioxide) is doped with 1 at% of the rare-earth Er. It leads to a diode-like behavior, which is associated with the presence of electric dipoles mainly at interface. Thermally stimulated depolarization current (TSDC) technique is also applied to this heterostructure in the dark and in the presence of monochromatic light from a He–Cd laser or a InGaN LED. The effect of monochromatic light on the possible formation or destruction of dipoles in this heterostructure system is analyzed by the I x V curves as well as by the TSDC data, considering the main types of defects in this structure: EL2 in the GaAs side, or oxygen vacancies and ionized Er ions in the SnO2 side. Photo-induced TSDC (PTSDC) points to the destruction of bands previously obtained in the dark, suggesting a large difference on the thermal and optical activation energies of defects. This effect is stronger with the illumination of a InGaN LED (2.76 eV) compared to He–Cd laser (3.80 eV) irradiation.

Antibacterial activity of SnO2 in visible light enhanced by erbium–cobalt co-doping

In this work, a series of SnO2 samples with systematically varied doping amounts of Er and Co were prepared via a precipitation–hydrothermal method. The results show that after Er doping, the 4I15/2 ground state of Er3+ jumps to the 4H11/2 higher-energy level, and the Er-doped SnO2 samples can efficiently convert low-energy light into high-energy light. Thus, Er doping is beneficial for improving the visible and near-infrared light response of SnO2 and thus enhances its photocatalytic performance. Furthermore, doping SnO2 with Co leads to a distortion of the SnO2 lattice. A proportion of the SnO2 lattice is replaced by Co atoms, which can effectively lower the bandgap of SnO2, widen its optical response range, and enhance its sunlight absorption efficiency. The photocatalytic antibacterial activities of pure SnO2, as well as SnO2 co-doped with Er and Co in visible light, were investigated under visible light using Escherichia coli. SnO2 shows the best antibacterial activity and electron–hole separation efficiency when co-doped with 1.5 mol. % Er and 1.5 mol. % Co (Er1.5Co1.5-SnO2). Gradient experiments reveal that mainly the reactive oxygen species affect the antibacterial activity of pure SnO2. The improved antibacterial performance of Er1.5Co1.5-SnO2 is attributed to the increased generation of·O2− and·OH. In addition, scavenger experiments reveal that·O2− is the key contributor to the enhanced antibacterial activity of SnO2.

Dipole behavior in thin film heterostructure composed of Er-doped SnO2 and GaAs: Influence of polarization bias, temperature and stray light

The heterostructure system GaAs/SnO2 is built by resistive evaporation of Er-doped SnO2 powder on the top of GaAs semi-insulating substrate. The SnO2 powder comes from the drying of SnO2 sol-gel solution. The possible formation of dipoles in this heterostructure is investigated by the thermally stimulated depolarization current (TSDC) technique, and the possibilities for dipole formation are explored, such as the EL2 defect in the GaAs side, oxygen vacancies and Er ions in the SnO2 layer. The dipole relaxation activation energies are found in the range 0.2 eV to 0.3 eV, in good agreement with the ionization energies of these defects. The main TSDC bands: 213 meV with peak of −298 pA, for positive bias, and 218 meV with peak of 128 pA for negative bias, are modified by stray (room) light, which may correspond to the second ionization level of oxygen vacancies in SnO2, which are excited by the room lights and do not return to the original orientation.

Synthesis and characterization of thermally evaporated Er-doped SnO2 thin films for photonic applications

In this study, different compositions of transparent films of erbium-doped tin oxide were created utilizing the thermal evaporation process on glass substrates. The tetragonal phase is verified by XRD analysis. The visible spectrum's strong transmittance was seen in the films. The films' transmission spectra ranged from 75 to 85% transmittance in the visible range with varying Er concentrations. Using Tauc's relation, values of the optical direct band gap have been calculated. The rutile phase of tin oxide is indicated by the Raman scattering peaks. PL measurements show thatonly the emission-related on a peak at 656 nm of Er3+ ions due to transition from 4I15/2 to 4F9/2 level and with the presence of doping, this emission becomes more intense. From the AFM measurements, the RMS roughness and grain size of films were computed. The results obtained show that these samples have wide applications in optoelectronic devices.

Enhanced room-temperature ammonia vapor-sensing activity of nebulizer spray pyrolysis fabricated SnO2 thin films: an effect of Er doping

In this work, we have coated 0, 1, 3, and 5 wt% of Erbium (Er)-doped tin oxide (SnO2) films on glass using a simple nebulizer spray pyrolysis method to make an ammonia vapor sensor with remarkable sensitivity. X-ray diffraction, Atomic force microscopy, Ultraviolet–visible spectroscopy and photoluminescence methods were employed to inspect the thin-film samples. Room-temperature ammonia vapor sensing was performed by a computer connected to the homemade gas-sensing system. The results obtained show that Er doping in SnO2 films gradually decreased the crystallite size with an increase of the surface area improving the sensing property of the vapor. A minimum optical band gap (i.e., 3.23 eV) is achieved for 5 wt% Er-doped film. The fabricated Er-doped SnO2 gas sensor showed response/recovery time highly dependent on dopant concentration. The Er concentration of 5 wt% doped SnO2 thin film showed maximum sensitivity of 91%, fast response, and recovery time of 29 and 7 s, respectively, due to high surface to volume ratio.

Effect of Er doping on flame-made SnO2 nanoparticles to ethylene oxide sensing

In this research, 0.05–2 wt% Erbium (Er)-doped SnO2 nanoparticles were synthesized for the first time by flame spray pyrolysis and their gas-sensing properties were methodically characterized. The structural analyses based on scanning/transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen sorption analysis, and photoluminescent spectroscopy suggested that nanocrystalline SnO2 nanoparticles were substitutionally doped with Er+3 species. The sensing films were prepared by powder pasting and spin-coating processes and their gas-sensing performances were evaluated in the temperature range of 200–400 °C under dry and humid air conditions. The test results reported that the optimum Er content of 0.1 wt% provided the optimally high and selective response of 347 to 30 ppm C2H4O with a short response time of ∼2 s and a low detection limit of 18 ppb, which were substantially better than those of undoped one at the best working temperature of 350 °C. The high selectivity was confirmed against CH2O, C3H6O, C2H5OH, NH3, C2H2, C2H4, H2, CH4, H2S, H2O and CO. Besides, the influence of humidity on C2H4O response of Er-doped SnO2 sensor was moderately low over a wide relatively humidity range of 0–80 %. The gas-sensing mechanisms were proposed with a new model describing the catalytic roles of p-type Er dopants to ethylene oxide adsorption.

Modification of SnO2 surface oxygen vacancies through Er doping for ultralow NO2 detection

Despite the high prevalence of tin oxide (SnO2) based sensors for detection of numerous toxic gases, they suffer from issues of cross-sensitivity and high operating temperatures. Herein, SnO2 lattice has been modified with highly catalytic erbium (Er) based rare earth metal to address aforementioned issues. Thin films of undoped and 1, 3, 5 wt% Er-doped SnO2 nanoparticles have been deposited by electron beam evaporation technique and influence of Er on structural and optical characteristics of SnO2 films has been investigated for gas sensing applications. The incorporation of Er in SnO2 thin films has been found to tune the concentration of oxygen vacancies, which can enhance the gas sensing parameters. The sensor with an optimized amount of Er (3 wt%) exhibits a maximum sensing response for 1 ppb of NO2 at room temperature (25°C) with improved selectivity and stability against humidity.

Photo-induced electrical behavior under gas adsorption on SnO2 -based heterostructures

Er-doped SnO2 thin films are produced by a combined technique where films are deposited by resistive evaporation from a precursor powder obtained by sol-gel. Films are deposited on different substrates and analyzed concerning the electrical conduction on different directions. The film conductivity (parallel to the surface) changed significantly when exposed to light, even though the photon energies are below the SnO2 bandgap energy (InGaN LED, 2.75 eV). The SnO2 films present distinct trapping characteristics when exposed to oxygen or carbon monoxide, in agreement with the behavior of metallic oxides, suggesting that surface defects act as adsorption sites. The photo-excitation is rather lower for a GaAs/SnO2 heterostructure sample where the GaAs layer is deposited by sputtering, since the direction of polarization (through the interface barrier, perpendicular to the sample surface) does not lead to significant increase in the sample current. When the bottom layer is a GaAs crystal wafer, the current magnitude increases drastically under the InGaN LED excitation. The results reported here contribute to the understanding of electrical transport and the influence of gas adsorption on evaporated SnO2 films deposited in diverse configurations on distinct substrates, and contributes to gas sensing applications.

Effect of erbium on the structural, morphological, and optical properties of SnO2 thin films deposited by spray pyrolysis

In the present work numerous compositions of Er-doped SnO2 thin films were made at 425 °C on a quartz glass substrate using spray pyrolysis method. The powder X-ray diffraction and X-ray photoelectron spectroscopy analysis confirms the tetragonal phase and surface chemical composition of as made Sn1-xErxO2 (x = 0.0, 0.01, 0.02, 0.03, 0.04, and 0.05) thin films. The grain size and RMS roughness of the films were estimated from the AFM measurements and the film surface has a saw-tooth-like morphology. The transmission spectra of the films are fallen in the visible range having between 60% and 80% transmittance with different Er concentration. The optical direct, indirect band gap and phonon energy values have been estimated. The photoluminescence measurements under excitation at 325 nm show three distinct emission peaks, a broad hump positioned at 390 nm, two sharp peaks at 420 nm related to tin interstitials, and a sharp peak at 700 nm related to oxygen vacancies. The Er3+ in SnO2 increased the oxygen vacancies to maintain charge balance and as a result the intensity of emission peaks increases with Er content.

Influence of thermal annealing on the properties of evaporated Er-doped SnO2

Er-doped tin dioxide thin films, deposited on glass substrates by a combination of sol-gel and resistive evaporation techniques, are investigated. The sol-gel route is used for powder preparation, which serves as material source for resistively evaporated thin films. The annealing temperature influences the Er3+ location, that reflects on the photoluminescence (PL) related to 2H11/2→4I15/2 and 4S3/2→4I15/2 Er3+ transitions. The lower annealing temperature, 300 °C, leads to PL emission, which vanishes for higher annealing temperatures. Annealing temperature above 300 °C enlarges the crystallites and allows diffusion of Er ions into the sample, increasing the population of substituted Sn sites. Then, the population of grain boundary located luminescent sites is decreased, leading to higher conductivity concomitant with absence of PL signal. Evaporated SnO2 films have the advantage of a stable electrical signal and the deposition on hydrophobic surfaces. Emission of evaporated SnO2 on GaAs substrates is also shown, yielding the substrate influence.

Highly sensitive gas sensor based on Er-doped SnO2 nanostructures and its temperature dependent selectivity towards hydrogen and ethanol

In the present work, impact of Er3+ doping on the response and selectivity of SnO2 based gas sensor has been investigated in detail. X-ray diffraction (XRD) results confirmed formation of a tetragonal rutile structure of undoped and erbium doped SnO2 nanoparticles. It has been observed that specific surface area of nanoparticles has increased with increase in dopant concentration. The oxidation states and presence of erbium in SnO2 lattice has been confirmed by X-ray photoelectron spectroscopy (XPS). Photoluminescence (PL) analysis revealed that concentration of oxygen vacancies increases with increase in dopant incorporation. It has been observed that 3% Er-doped SnO2 sensor exhibited enhanced sensor response and temperature dependent selectivity towards ethanol and hydrogen at 240 and 360 ℃ respectively. The enhanced sensor response of the fabricated sensor has been ascribed to large surface area, enormous oxygen vacancies and elevated surface basicity of doped nanoparticles used. The tunable dual selectivity of 3% doped sensor towards ethanol and hydrogen makes it a perfect candidate for ethanol-hydrogen sensing for ethanol steam reforming systems combined to fuel cells.

Influence of Hydrothermal Temperature on the Optical Properties of Er-Doped SnO2 Nanoparticles

This work reports on crystallization and optical properties of SnO2:Er3+ with a fixed Er3+ concentration of 0.25 at.%, prepared by the hydrothermal method. Crystal structure and morphology of the materials were studied by x-ray diffraction (XRD) and field emission transmission electron microscopy. Characteristic light emission at 1.5 μm for radiative 4 I 13/2 → 4 I 15/2 transitions within the 4f electron shell of Er3+ ions was studied by photoluminescence (PL) and excitation spectroscopy. The optical bandgap of the nanoparticles was examined by ultraviolet--visible absorption measurements. SnO2:Er3+ nanoparticles were formed in single-phase tetragonal rutile structure by applying temperatures ranging from 120°C to 200°C during the hydrothermal synthesis. An average crystal size of 5 nm was estimated by the Scherrer equation using the XRD data and found to be independent from the investigated hydrothermal temperatures. Whereas, the Er3+-related PL intensities were found to increase strongly with the hydrothermal temperature.

Hydrothermal synthesis and characteristic photoluminescence of Er-doped SnO2 nanoparticles

We report the characteristic photoluminescence (PL) spectra of erbium ion (Er3+)-doped tin dioxide (SnO2)nanoparticles. The materials were prepared via hydrothermal method at 180°C with in 20h by using various Er3+ ion concentrations ranging from 0.0 to 1.0at%. After the synthesis, the materials were characterized through X-ray diffraction and high-resolution transmission electron microscopy. Crystallite SnO2 and its average particle diameter of approximately 5nm did not change with Er3+ ion dopant concentration. Photoluminescence spectra showed the characteristic light emission from the Er3+ ions. The PL excitation spectra referred to an efficient energy transfer to Er3+ ions in the presence of SnO2nanoparticles. The most intense Er-related emission of SnO2:Er3+ nanoparticles in near infrared region was found in samples containing an Er3+ ion concentration of 0.25at%. Although the absorption bandgaps of the materials were identified at approximately 3.8eV, we found that efficient excitation comes with low excitation energy band edge. Excitation is possibly involved in shallow defects in SnO2 nanoparticles.

Highly sensitive formaldehyde resistive sensor based on a single Er-doped SnO2 nanobelt

SnO2 nanobelts (SnO2 NBs) and Er3+-doped SnO2 nanobelts (Er–SnO2 NBs) were synthesized by thermal evaporation. The obtained samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersion spectrometer (EDS), and X-ray photoelectron spectrometer (XPS). It is found that Er–SnO2 NBs have a good morphology with smooth surface and their thickness are about 30nm, widths between 200nm and 600nm, and lengths 30–80mm. The nanobelts with good morphology were taken to develop sensors based on a single Er–SnO2 NB/SnO2 NB for studying sensitive properties. The results reveal that the response of a single Er–SnO2 nanobelt device is 9 to the formaldehyde gas with a shorter response (recovery time) of 17 (25) s.

Improved electrical transport in lightly Er-doped sol–gel spin-coating SnO2 thin films, processed by photolithography

Sol–gel spin-coating SnO2 thin films were deposited and processed through positive photolithography (liftoff), avoiding surface interaction with gaseous oxygen species and leading to samples with higher stability and data reproducibility, when submitted to electrical characterization. Processing includes: (1) a narrow conduction channel, (2) the assembly of electric contacts by ultrasound soldering, (3) deposition of an insulating layer, preventing the surface contact with atmospheric oxygen, which contributes for reliable measurements and the possibility of measuring SnO2 matrix properties without influence of adsorbed oxygen. Lightly Er-doped SnO2 sample (0.05 at.%), processed by this manner, has allowed the observation of a maximum about 50 K, in the temperature-dependent resistivity curve, which has not been found previously. This result is probably related to the combination of free electron concentration, which grows with temperature, and the grain boundary scattering, which decreases with temperature, and is the dominant mechanism for sol–gel SnO2. The processing also assures a remarkable reproducibility in the decay of photo-induced conductivity, yielding reliability to apply a modeling for the determination of important decay parameters, such as capture energy and grain boundary potential barrier.

Long-range ferromagnetic order induced by a donor impurity band exchange in SnO2:Er3+ nanoparticles

In this work, the structural and magnetic properties of Er-doped SnO2 (SnO2:Er) nanoparticles are reported. The SnO2:Er nanoparticles have been synthesized by a polymer precursor method with Er content from 1.0% to 10.0%. X-ray diffraction results indicate the formation of only the rutile-type structure in all samples. The estimated mean crystallite size shows a decrease from ∼10 to ∼4 nm when the Er content is increased from 1.0% to 10.0%. The particle size values have been corroborated by transmission electron microscopy technique. The thermal dependence of the magnetization is consistent with the 3+ oxidation state of erbium ions for all samples. A strong paramagnetic-like behavior coexisting with a ferromagnetic phase has been determined for samples with Er content below 5.0%. Above this concentration, only a paramagnetic behavior has been determined. Isothermal magnetization curves are consistent with the occurrence of long-range ferromagnetic order mediated by donor electrons forming bound magnetic polarons which overlap to produce a spin-split impurity band.

Nanoparticle characterization of Er-doped SnO2 pellets obtained with different pH of colloidal suspension

SnO2:2 at. %Er xerogel samples were obtained by sol-gel technique from colloidal suspensions with distinct pHs. The evaluation of critical regions inside the nanocrystallite is fundamental for the interpretation of the influence of pH on the emission data. In this way, the nanocrystal depletion layer thickness was obtained with the help of photoluminescence, Raman, X-ray diffraction, and field-emission gun scanning electron microscopy measurements. It was observed that acid suspensions (pH < 7) lead to high surface disorder in which a larger number of cross-linked bonds Sn-O-Sn among nanoparticles are present. For these samples, the nanoparticle depletion layer is larger as compared to samples obtained from other pH. Photoluminescence measurement in the near infrared region indicates that the emission intensity of the transition 4I13/2 → 4I15/2 is also influenced by the pH of the starting colloidal suspension, generating peaks more or less broadened, depending on location of Er3+ ions in the SnO2 lattice (high or low symmetry sites).

Experimental evidences of substitutional solution of Er dopant in Er-doped SnO2 nanoparticles

Structural and hyperfine properties of Er-doped SnO2 nanoparticles synthesized by a polymer precursor method are reported in this study. X-ray diffraction patterns of samples doped with erbium up to 10 mol % indicate the formation of the tetragonal rutile phase. The mean crystallite size shows a rapid decrease from ~12 nm for the undoped sample down to ~4 nm for the 10 mol % Er-doped sample. Structural changes as a function of the Er content, i.e., changes in the lattice constants, Sn–O bond distances and bond angles, strongly suggest the substitutional solution of Er3+ ions and the onset of oxygen vacancies throughout the SnO2 lattice. No dipolar-magnetic interaction is determined from the Mossbauer spectra which are well resolved by fitting with a distribution of electric-quadrupole doublets. Changes observed in the quadrupole splitting as a function of the Er content have been associated to the local strain induced by the cationic size mismatch and oxygen vacancies. This local strain affects the lattice contribution of the electric field gradient. The linear increase of the isomer shift is assigned to the enhancement of the oxygen vacancies as the Er content is increased. It is found that the oxygen vacancies provide with conduction electrons to the Er-doped SnO2 nanoparticulated system, therefore modifying its electronic properties.

Synthesis and Characterization of Small Dimensional Structures of Er-Doped SnO2 and Erbium–Tin–Oxide

Microtubes of Er-doped SnO2, as well as nanorods and nanoparticles, have been fabricated by a thermal evaporation deposition method at temperatures between 1400 and 1500 degrees C, by using a pellet of compacted SnO2 and Er2O3 powder mixture as precursor. Er2Sn2O7 has been also detected by X-ray diffraction spectroscopy. Energy dispersive X-ray spectroscopy and photoelectron spectroscopy measurements demonstrate that the microtubes contain a small amount of Er, below 0.5 at. %, different from regions from the surface of the pellets where the tubes grow, which shows a variable Er concentration up to 25 at. %. Cathodoluminescence spectra confirmed the presence of Er in the microtubes, as well as in the surface of the pellet, where emissions in the visible and the infrared range at 1.87, 2.23, and 0.81 eV are observed. The luminescence signal varies as a function of the thermal parameters used during the microtubes growth. The mechanisms of Er incorporation are discussed.