Ce-doped ZnO Thin Films Research Articles

Synthesis and characterizations of Ce-doped ZnO thin films for radiation shielding

In this research, different amounts of Ce-doped ZnO thin films were synthesized using the spray pyrolysis method. Structural, morphological and optical properties of these synthesized films were investigated. In XRD analyses, wurtzite (hexagonal) structures were observed in the films. In SEM analysis, there were changes in the surface morphology of the films with doping, and in cross-section measurement, the thickness of the films was measured to be approximately 1.2 μm. In UV–vis spectrometry analysis, it is seen that the effect of Cerium contribution on optical transmittance and band gap positively affects shielding. NaI(Tl) detector and gamma energies of 384, 1173, and 1333 keV have been used to investigate the radiation protection properties of these synthesized films. As a result of these measurements, linear attenuation coefficient (LAC) values have been obtained. Radiation shielding parameters have been calculated with these (LAC) values. The Mass Attenuation Coefficient (MAC), Half Value Layer (HVL), Tenth Value Layer TVL (and) Mean Free Path (MFP) values have been also calculated using this LAC result. According to these results, Ce-doped ZnO films were found to be effective in radiation shielding.

Significance of microstrain in impacting band gap and photoluminescence behavior of Ce-doped ZnO thin films deposited via sol-gel process

The purpose of this study is to analyse the importance of micro-strain in affecting the band gap and photoluminescence (PL) intensity of sol-gel-spin-coated Ce-doped ZnO thin films on glass slides. The presence of the (100) plane in the fabricated thin film was discovered using x-ray diffraction thereby indicating the presence of strongly orientated monocrystalline ZnO hexagonal wurtzite phase. On doping with Ce, the micro-strain in the ZnO thin films changed from (2.49–4.84) × 10–3, and the crystallite size ranged from 26.23 to 43.03 nm. UV-visible spectroscopy revealed that the optical transparency of the undoped and Ce-doped ZnO films was between 60 to 85 percent, however the doped films’ absorption dip was slightly shifted from 378 to 380 nm. For Ce-doped ZnO thin films, the increase in band gap values determined using Tauc’s plot was in the range of 3.19 to 3.44 eV. No change in the peak of UV emission was visible in the PL emission spectra after Ce doping. The micro-strain brought on by doping ZnO with Ce controlled the decrease in PL intensity. On doping with Ce up to 3 at.%, PL intensity and micro-strain both reduced, then climbed till Ce 5 at.%, and ultimately declined when the Ce content was 6 at.%. According to studies using scanning electron microscopy, the undoped ZnO film morphology was characterised by spherical particles with rod-like growth structures. For 1, 2, 5, and 6 at.% Ce-doped ZnO thin films, this structure was changed to a nanorod-like structure with small nanorods attached to a long rod. But lengthy chain linkage structures were found in the event of 3 at.% Ce doping. The preceding results are discussed from a doping perspective.

Dielectric and Magnetic Properties of Rare-Earth Metal Ce-Doped ZnO Thin Films

Ce-doped ZnO thin films were fabricated by sol–gel dip coating method with varying Ce concentrations of 1–5 at.wt.%. The influence of Ce doping on magnetic and dielectric properties has been investigated. Vibrating sample magnetometer results reveal that the Ce-doped ZnO material has a soft nature. The study of magnetic properties confirmed the ferromagnetic behavior at room temperature for all the synthesized thin films. The localized states of Ce atoms are the main contribution to the magnetic moment. Crystallinity of thin films is highly dependent on the magnetic properties. The increased percentage of Ce reduces the saturation magnetization and coercivity. By using an impedance analyzer, variation in the results of dielectric constant, dielectric loss and AC conductivity of prepared thin films at room temperature as a function of frequency ranges from 100 Hz to 1 MHz were investigated. The normal behavior of dielectric dispersion was shown by the thin films, as evidenced by the reduction of the dielectric constant and dielectric loss with the increase in frequency due to Maxwell–Wagner interfacial polarization. Similarly, dielectric results showed that the increase in frequency enhanced the AC conductivity. It is used to evaluate the minimum distance of hopping, maximum height of the barrier and the localized density of states at the Fermi level. The induced spin polarization is found for Ce doping.

Realizing luminescent downshifting in ZnO thin films by Ce doping with enhancement of photocatalytic activity

ZnO thin films doped with Ce at different concentration were deposited on glass substrates by spray pyrolysis technique. XRD analysis revealed the phase purity and polycrystalline nature of the films with hexagonal wurtzite geometry and the composition analysis confirmed the incorporation of Ce in the ZnO lattice in the case of doped films. Crystalline quality and optical transmittance diminished while electrical conductivity enhanced with Ce doping. Ce doping resulted in a red-shift of optical energy gap due to the downshift of the conduction band minimum after merging with Ce related impurity bands formed below the conduction band in the forbidden gap. In the room temperature photoluminescence spectra, UV emission intensity of the doped films decreased while the intensity of the visible emission band increased drastically implying the degradation in crystallinity as well as the incorporation of defect levels capable of luminescence downshifting. Ce doping showed improvement in photocatalytic efficiency by effectively trapping the free carriers and then transferring for dye degradation. Thus Ce doped ZnO thin films are capable of acting as luminescent downshifters as well as efficient photocatalysts.

Effect of Li codoping on highly oriented sol-gel Ce-doped ZnO thin films properties

Ce-doped and (Ce, Li) codoped ZnO thin films have been deposited onto glass substrates by sol–gel dip coating method. The effects of Ce–Li co-doping for 0.1at.% Ce and 0–20at.% Li on structural, morphological and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), UV–Vis–NIR spectrophotometry and photoluminescence spectroscopy (PL). XRD analysis revealed that all the films were highly c-axis oriented and had a hexagonal wurtzite structure. AFM images showed that film morphology and surface roughness were influenced by Li doping concentration. UV–Vis–NIR measurements indicated that the film transmission decreases with increasing Li content and the optical band gap was dependent on the Li concentration. Room temperature PL spectra put into evidence that emission is significantly influenced by Li content. In particular, it was found that the visible emission intensity of the film with 20at.% Li codoping in 0.1at.% Ce-doped ZnO is approximately 30 times greater than that of the undoped film.

Nanostructured Cerium-doped ZnO thin film – A breath sensor

Breath analysis has emerged as one of the accurate diagnostic techniques, which can be used to correlate disease conditions with the abnormal concentrations of certain biomarkers present in the exhaled breath. In this background, thin film based chemi-resistive Cerium-doped ZnO sensors were developed for detecting acetone and ethanolamine, which are the notable biomarkers of diabetes mellitus and carcinoma respectively. Ce-doped ZnO thin films were deposited on glass substrates using spray pyrolysis technique. X-ray diffraction patterns confirmed the formation of Ce-doped ZnO thin films with polycrystalline hexagonal wurtzite structure. Scanning electron micrographs and optical absorption spectra of Ce-doped ZnO thin films revealed the decrease in average grain size and increase in band gap respectively with an increase in Ce-dopant concentration. ZnO films with 0.004 and 0.008M of Ce-dopant concentrations showed a better room temperature sensing response towards acetone and ethanolamine respectively. Highly selective nature of the developed sensing elements towards acetone and ethanolamine with swift response and recovery times can be considered as a non-invasive and cost effective method for the detection of diseases like diabetes mellitus and carcinoma.

The influence of Ce doping on the structural and optoelectronic properties of RF-sputtered ZnO films

Using X-ray diffraction, UV-Visible spectroscopy, XPS and photoluminescence (PL) measurements, the structural, optical and electronic properties of ZnO and Ce-doped ZnO thin films were investigated; the films were deposited on glass substrates by RF reactive-magnetron sputtering and post-annealed at $$300\,^{\circ }\hbox {C}$$ in an oxygen atmosphere. Under similar deposition conditions, both films crystallized into hexagonal wurzite lattice structures. The pure ZnO film exhibited a c-axis preferential orientation, whereas the Ce-doped exhibited an a-axis preferential orientation. The films display uniform textured surfaces with columnar-like microstructures. The UV-Vis spectra showed high transparencies of 90 % on average for both films. Band gaps of $$\hbox {E}_{g}=3.23\,\hbox {eV}$$ and $$\hbox {E}_{g}=3.27\,\hbox {eV}$$ for pure and Ce-doped film, respectively, were measured. The doped film spectrum was shifted to the blue as a result of the Burstein-Moss effect. The XPS spectra show that the VB edge of the doped film shifts toward lower binding energy, at $$\sim $$ 1.3 eV below $$\hbox {E}_{F}$$ , while the VB edge of the pure film is located at $$\sim $$ 2.0 eV below $$\hbox {E}_{F}$$ . Additionally, $$\hbox {Ce}^{3+}$$ and $$\hbox {Ce}^{4+}$$ ions coexist in the ZnO matrix in fractions of $$\sim $$ 70 and $$\sim $$ 30 %, respectively. The PL spectra show that both types of ions induce extra electron states that allow multiple emission peaks in the blue–green region.

Blue luminescence from Ce-doped ZnO thin films prepared by magnetron sputtering

The photoluminescence properties of undoped and Ce-doped ZnO thin films that were prepared by DC magnetron sputtering were investigated. It was found that the incorporation of Ce could intensively affect the structural, optical, and photoluminescence properties of the ZnO thin films. The undoped ZnO thin films showed a sharp UV luminescence, whereas the Ce-doped ZnO thin films showed a broad blue luminescence. The effects of excitation wavelength and annealing atmosphere on the photoluminescence properties of Ce-doped ZnO thin films were also studied. After post-annealing in air and oxygen atmospheres, the blue emissions of the prepared films were drastically suppressed. Our results indicate that the blue emissions of Ce-doped ZnO thin films are related to zinc interstitials and the intrinsic transition of Ce3+ ions.

Effects of Ce Doping on the Properties of ZnO Thin Films Prepared by DC Reactive Magnetron Sputtering

The ZnO and ZnO:Ce thin films were prepared by DC reactive magnetron sputtering. The structure, surface morphology, optical and photoluminescence properties of ZnO:Ce thin films were investigated. The XRD results indicated that all the samples exhibited a hexagonal wurtzite structure. The surface morphology of the films was sensitive to the Ce concentration. All the films had a higher average transmittance (more than 85%) in the visible region and a strong absorption near the band-edge of ZnO. The photoluminescence properties of the Ce-doped ZnO thin films were also studied. Blue emissions were observed from the ZnO:Ce thin films. Our results indicated that the photoluminescence properties of ZnO thin films doped with low Ce concentration were related to the intrinsic transition of Ce3+ ions. However, when the Ce concentration increased, Zni also played an important role.