Optical Properties Of CeO2 Research Articles

Enhanced structural and optical properties of CeO2:ZnO nanocomposites for photocatalysis application

Enhanced structural and optical properties of CeO2:ZnO nanocomposites for photocatalysis application

Structural and Optical Properties of Bismuth-doped Cerium Oxide Prepared at a Low Temperature

Cerium oxide (CeO2) is a functional material with excellent physicochemical properties. Its properties can be modified by doping with different elements, including bismuth, which can be done through various synthesis methods. The precipitation method combined with ultrasonic radiation was used to synthesize bismuth-doped cerium oxide (CeO2:Bi) at a low temperature of 200oC. In this study, we investigate the alteration of structural and optical properties of as-prepared CeO2:Bi by subjecting it to additional calcination at a high temperature of 500oC. The structural and optical properties of CeO2:Bi were characterized using thermal gravimetric analysis, X-ray diffraction, Scanning Electron Microscope-Energy Dispersive X-Ray, Fourier Transform Infrared spectroscopy, and UV-Visible spectroscopy. The additional calcination produced a less significant weight-loss percentage than the as-prepared CeO2:Bi observed from the gravimetric curve. The Fourier transform infrared spectrum revealed the loss of a small number of hydroxyl molecules trapped on the CeO2:Bi surface when additional calcination was subjected. Based on the X-ray diffraction spectra, additional calcination results in the smallest crystallite size and compressive strain without the changed cubic crystal structure of CeO2:Bi. The successful doping of Bi in CeO2 was confirmed by the composition analysis from Energy Dispersive X-Ray measurement. Scanning electron microscope image showed spherical and agglomerated particles of calcined CeO2:Bi. The optical properties of both CeO2:Bi possessed similar trend absorption spectra and almost the same band gap energy. The results indicated that the calcination of as-prepared CeO2:Bi at a temperature of 500oC did not affect its structural and optical properties significantly. Thus, combining ultrasonic radiation with precipitation is an advantageous method to synthesize at a low temperature of stable CeO2:Bi crystalline.

Exploring structural, electronic, magnetic, and optical properties of CeO2-X (X = Pt/Ni) doped and Pt-Ni co-doped CeO2 for optoelectronic applications

Employing DFT technique, we perform Pt/Ni doping and Pt-Ni co-doping into CeO2. We study the structural, electronic, magnetic, and optical properties of CeO2 with selected dopants using Wien2k code. Spin-polarized DOS illustrate non-magnetic character of pure CeO2 while Pt/Ni/Pt-Ni doping yields magnetism into CeO2 with magnetic moment values of 2.2502 μ B, 2.5683 μ B, and 3.9190 μ B, respectively. Active participation of Ce 4f-, Pt 4d- and Ni 3d-states at the Fermi level suggests remarkable improvement in the conduction process. p-d hybridization is observed and it produces good response in electronic properties. Pt:CeO2 and Pt-Ni:CeO2 exhibit blueshift while Ni:CeO2 exhibit redshift in absorption spectrum. We notice an enhancement in optical absorption and conductivity with decreased reflectivity of these proposed materials in the UV region. Tuning of absorption spectra and decrease in band gap of these materials indicate their uses for photocatalytic, photonic, optoelectronics and power electronic devices.

The effect of stress on electronic structure and optical properties of CeO2

The effect of stress on the electronic structure and optical properties of CeO2 is studied using the ultrasoft pseudopotential plane wave method based on density functional theory. The results show that the band gap decreases quasi-linearly with the negative stress increasing and increases quasi-linearly with the increase of positive stress. Combining with the density of states (DOS) analysis, the main reason for the change of the band gap is Ce 4f electrons are significantly affected by the stress. When the stress changes from −25 to 30 GPa, the DOS of Ce 4f is far away from the Fermi level and gradually decreases. The influence of stress on optical properties mainly shows two obvious features. The first feature is that the optical properties are gradually appeared as the stress changes from −25 to 30 GPa and the optical edges are moved to high energy direction, in the energy range of 0–3 eV. Another feature is that there is an obvious peak value under the stress of −25–0 GPa, but does not significantly change under the stress of 0–30 GPa, in the energy range of 3–6 eV. The results show that the negative stress enhances the electronic transition, which is beneficial to improve the utilization of light.

Enhanced photocatalytic activity with metal ion doping and co-doping in CeO2 nanoparticles

In the present work effect of Yttrium (Y) and Zinc (Zn) doping and co-doping on the structural and optical properties of CeO2 are studied to evaluate its photocatalytic activity for the removal of crystal violet dye. A series of Y (2–10 mol %) and Zn (2–10 mol %) doped CeO2 are synthesized via co-precipitation route. The synthesized samples were characterized via X-ray diffraction, Transmission electron microscopy, Energy Dispersive X-ray analysis, Fourier transform infrared spectroscopy and Raman spectroscopy. The presence of different functional groups are studied via FTIR and Raman spectroscopy. XRD results confirmed the formation of cubic fluorite structured CeO2 with average crystallite size ∼ 3–7 nm. Y doping in CeO2 resulted an increase in the crystallite size, whereas Zn led to decrease in the crystallite size. The photocatalytic activity is studied via UV–visible spectroscopy technique by examining the absorbance spectra. Among the various samples, 8 mol % Y-doped CeO2 exhibited 100% degradation efficiency within 7 h, while 8% Zn-doped CeO2 exhibited 100% degradation efficiency towards crystal violet (CV) dye within 5 h under UV–visible illumination. In case of Y, Zn co-doped CeO2 samples, 100% degradation efficiency towards CV dye was achieved within 3 h under UV–visible light. The present study shows that the metal ion co-doping can lead to enhancement in the degradation efficiency by several folds as compared to doped samples.

Study of electronic, thermoelectric and optical properties of environment friendly Mg doped CeO2 for energy harvesting devices

According to the recent investigations on transition metal oxides it is shown that they have exceptional thermoelectric and optical properties. In this context, present study reports the effect of Mg doping on the electronic, thermoelectric, and optical properties of CeO2, through experimental and DFT calculations. These results are obtained, supposedly due to the ability of ceria nanoparticles to rapidly store and release oxygen, as it acts as an oxygen buffer. Further optimization can be expected by doping Mg which can increase the electrical conductivity of the ceria nanoparticles, thereby increasing the figure of merit. Effect of Mg can also be seen in the electronic and optical behavior of ceria nanoparticles as the band-structure of the system changes. All these changes result in thermoelectric figure of merit approaching to 2 ± 0.2 at room temperature and above.

Gadolinium doped CeO2 for efficient oxygen and hydrogen evolution reaction

Hydrogen evolution reaction (HER) is a significant half reaction in water splitting and it is spirit of energy storage and conversion applications. Recently, high durability and catalytic activity of effective electrodes are necessary to enlarge clean and sustainable energy sources. However, overcoming the overpotential and to improve HER and OER performance is still one of the complicated tasks. Hence, in this present work, gadolinium (Gd) doped cerium oxide (CeO2) was successfully synthesized through a facile co-precipitation method. High intense peak at 28.5° clearly indicated CeO2 cubic structure formation identified by using X-Ray diffraction. The optical phonon mode of F2g and oxygen vacancies mode was detected by using Raman spectra. The optical properties of CeO2 were detected with help of photoluminescence spectroscopy (PL). Fourier-transform infrared (FTIR) spectroscopy confirmed Ce-O vibration of CeO2 crystal existence. Surface morphology of CeO2 was thoroughly studied by using SEM images. HER and OER activity of pristine and Gd doped CeO2 was thoroughly investigated with the help of linear sweep voltammetry. Compared to pristine CeO2, high content of Gd doped CeO2 exhibited excellent HER and OER activity with low overpotential (99 mV for HER and 369 mV for OER) and small Tafel slope (211 mV/dec for HER and 183 mV/dec for OER). Addition of rare earth metal influenced the structural and catalytic properties of optimized metal oxide. Hence, the incorporation of Gadolinium in CeO2 plays a crucial role to enhance both HER and OER performance and it is one of the good candidates for energy conversion applications.

Comparison of structural and optical properties of CeO2 and CeO2:Eu3+ nanoparticles synthesized via sol–gel and flame spray pyrolysis methods

Over the last decades, a considerable attention has been drawn on the cerium dioxide (ceria, CeO2) due to promising changes in physical and chemical properties in nanoscale. The researches on CeO2 and its structural and morphological modifications have brought about remarkable applications as optical devices, sensors, medical equipments and luminescent materials. For instance, rare earth (RE) ion-doped cerium oxides have exhibited enhanced peculiar optical, catalytic and magnetic properties with respect to the dopant-free CeO2 nanoparticles. Herein we aimed to compare characteristics of undoped (CeO2) and europium (Eu3+) doped ceria (CeO2:Eu3+) nanoparticles synthesized by sol–gel (SG) and one-step flame spray pyrolysis (FSP) methods. In this work, fabricated nanoparticles were evaluated in terms of the structural, morphological, chemical and optical properties by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron (XPS) and photoluminescence spectroscopy (PL), respectively. Nanoparticles in the intended crystalline CeO2 structure were obtained for both methods. Spherical particles in nanoscale (particle size < 100 nm) and sharp edged blocky particles in sub-micron size (particles size range 200–1000 nm) were produced through FSP and SG, respectively. Nevertheless, no significant difference due to the difference in particle size was observed in optical properties. On the other hand, Eu3+ doped particles of both methods exhibited longer decay time than the undoped particles.

Study on Enhanced Antibacterial and Cytotoxicity of Pure and Cadmium Doped Cerium Oxide against Gram-Positive and Gram-Negative Bacteria

Pure and Cadmium (Cd) doped Cerium oxide nanoparticles (CeNPs) have been synthesised by the simple chemical co-precipitation technique. Cadmium ions of concentrations 1, 3 and 5 mol% were doped to investigate their influence on the structural and optical properties of CeO2. The synthesised samples have been subjected to X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and high-resolution transmission electron microscopy (HRTEM). The XRD and Raman patterns have witnessed the cubic structure of the cerium oxide nanoparticles. The average particle size of CeO2 was found to be around 10 nm. SEM image has also ascertained that the grain size of pure CeO2 appeared is bigger than that of the Cd-doped, which intern indicates the grain growth upon doping. Besides, the antibacterial activity of the cadmium doped cerium oxide nanoparticles against some human pathogens revealed that they have exhibited the maximum zone of inhibition against gram-positive bacteria than the gram-negative species. Further, the cytotoxic effect of Cd-doped CeO2 sample is examined in cultured (MCF-7, A549 and Hep-2) cell.

Longer ozonolysis time induced CeO2 hexagonal nanostructures from nanocubes

Abstract Cerium oxide (CeO2) nanostructures were synthesized using an ozonolysis assisted co-precipitation method, while varying the ozonolysis reaction times for 1, 2, 3 and 4 h in the systems. The effect of ozonolysis reaction time on the morphology and optical properties of CeO2 was investigated. The resulting products were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis), photoluminescence spectroscopy (PL) and BET surface area analysis. The XRD patterns confirm a face-centered cubic (FCC) CeO2 having crystalline sizes ranging from 8.5 to 10 nm. From the TEM images, longer ozonolysis reaction times more completely transform the morphology of CeO2 nanoparticles from a nanocube-like shape into hexagonal CeO2 nanostructures. FTIR spectra show that the peaks in the region of 400–750 cm−1 are due to Ce–O stretching vibrations. The UV–Vis spectra of all samples show strong absorption at 285 nm with a weak absorption peak around 360 nm. The band gap energy is independent of ozonolysis reaction time. The photoluminescence spectra show characteristics peaks of CeO2 nanoparticles. Adsorption-desorption isotherms of CeO2 show a typical IUPAC type IV pattern and their pore size is 3.28 nm.

Co-doping effect of monovalent alkali metals on optical properties of CeO2:Eu nanophosphor prepared by spray pyrolysis and application for preparing pearlescent pigments with red emission

Nano-sized CeO2:Eu/M (M = alkali metal) red phosphor was synthesized by spray pyrolysis. Three alkali metals (Li, Na and K) were introduced to find the most suitable codopant in terms of luminescent intensity and nano-sized phosphor synthesis. The emission intensity of CeO2:Eu was largely improved about twice or more by the codoping of monovalent alkali metal due to the charge compensation effect and the improvement of crystallinity. The emission enhancement was largest when Na was codoped and the emission intensity showed a linear relationship with the crystallite size regardless of the kind of alkali metal. The particle size increased with the codoping of alkali metals, but the resulting phosphor still had a nanosize of 100–200nm. When Na was used, the resulting powders exhibited less aggregation characteristics compared with Li and K. Thus, it was concluded that the Na codoping was most suitable for the synthesis of nano-sized CeO2:Eu/M phosphors with improved luminescence. The prepared CeO2:Eu/Na nanoparticles were coated on the surface of commercially available pearl pigment. The resulting pearlescent pigment was found to have sufficient red emission to be visible to the naked eye when illuminated by an LED UV lamp.

Simple hydrothermal synthesis and optical properties of CeO2 with an open hierarchical structure composed of many nanotubes

In this study, CeO2 with an open hierarchical architecture have been successfully synthesized via a simple hydrothermal technology. X-ray diffraction (XRD) inferred that the synthesized CeO2 hierarchical structures exhibited a fluorite cubic structure. It is found that numerous nanotubes of dozens of micron in length, 50–100 nm in thickness of wall and about 200 nm in average diameter are connected at one end and diverge at the other end to form an open hierarchical architecture and there are Ce3+ ions and oxygen vacancies in surface of samples. There is a red-shifting in the band gap of the material compared to bulk one, which is mainly attributed to the effects of the Ce3+ ions, oxygen vacancies and the morphology of the material.

Solution combustion synthesis, photoluminescence and X-ray luminescence of Eu-doped nanoceria CeO2:Eu

Rare earth Eu3+-doped nanoceria with an average size of 60 nm were synthesized by urea–nitrate solution combustion reaction. The microstructure and morphology of the samples were characterized by X-ray diffraction patterns (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (SEM). The host is confirmed to be pure CeO2. However, there are two distinct oxygen surroundings due to the substitution of Ce4+ species with Eu3+ ions. The optical properties of CeO2:Eu were investigated by photoluminescence and X-ray luminescence spectroscopy. The samples can be excited with 360 nm (ultra-violet light, the charge transfer band of O–Ce) and 466 nm (blue light, the Eu3+ 7F0 → 5D2 transition) respectively, and exhibit typical red-light emission of Eu3+. At low Eu3+ concentrations, the sample can be effectively excited with 360 nm. With the increase of the Eu3+ concentration, the dominant excitation wavelength is changed to 466 nm, which is beneficial for use in solid state lighting because of the coincidence with the emission of GaN chips. Under the excitation of 466 nm, the quenching concentration of Eu3+ can be increased to 16 mol% due to the interface effects of the nanoscale materials. Furthermore, the X-ray luminescence of CeO2:Eu also shows strong red-light emission, manifesting that the material is a promising scintillator for radiation detection.

Evidence of Coulomb correction and spin–orbit coupling in rare-earth dioxides CeO2, PrO2 and TbO2: An ab initio study

The current study investigates the structural, elastic, electronic and optical properties of CeO2, PrO2 and TbO2 using the full potential (linearized) augmented plane wave plus local orbital method within the Wu–Cohen generalized gradient approximation (GGA) with Hubbard (U) correction and spin–orbit coupling (SOC). The GGA+U implementation lead us to describe correctly the relativistic effect on 4f electrons for CeO2. We clarify that the inclusion of the Hubbard U parameter and the spin–orbit coupling are responsible for the ferromagnetic insulating of PrO2 and TbO2. The magnetic description is achieved by the spin-density contours and magnetic moment calculations, where we show the polarization of oxygen atoms from the rare earth atoms. The mechanical stability is shown via the elastic constants calculations. The optical properties, namely the dielectric function and the reflectivity are calculated for radiation up to 12eV, giving interesting optoelectronic properties to these dioxides.

Dependence of pressure on elastic, electronic and optical properties of CeO2 and ThO2: A first principles study

The phase transformation of CeO2 and ThO2 from fluorite to cotunnite-type structure under pressure is predicted within the density functional theory implemented with the GGA-PW91 method, the pressure induced structural phase transition occurs at 28.9GPa for CeO2 and 29.8GPa for ThO2. These values are in excellent agreement with the experimentally measured data. The elastic, electronic and optical properties at normal as well as for high-pressure phase have been calculated, particular attention is devoted to the cotunnite phase. Further, the dependence of the elastic constants, the bulk modulus B, the energy band gaps and the dielectric function on the applied pressure are presented.

Elastic and optical properties of CeO2 via first-principles 2 calculations

Elastic and optical properties of CeO2 via first-principles 2 calculations

Controlled synthesis of CeO2 nanorods by a solvothermal method

Pure phase CeO2 nanorods (about 40–50 nm in diameter and0.3–2 µm in length) were synthesized through a solvothermal synthesismethod. The addition of ethylenediamine is critical to obtainCeO2 nanorods. Other experimental conditions, such as the solvent composition, surfactant andthe cerium source precursor were of importance in the final product morphology. Thereaction temperature and reaction time also had significant influence on the yield ofCeO2 nanorods. A possible formation mechanism ofCeO2 nanorods was discussed mainly based on the dependences of controllingparameters on the final morphologies. In addition, the optical properties ofCeO2 nanorods were investigated. The UV–visible adsorption spectrum and photoluminescence spectrum ofthe CeO2 nanorods showed unusual red-shift and enhanced light emission, respectively.

Experimental and Theoretical Characterization of the Optical Properties of CeO2, SrCeO3, and Sr2CeO4 Containing Ce4+ (f0) Ions

In an effort to find new UV absorbers, the optical properties of CeO2, SrCeO3, and Sr2CeO4 were examined by UV−visible diffuse reflectance measurements and electron energy-loss spectroscopy (EELS), and their electronic structures were investigated on the basis of first-principles density functional theory (DFT) calculations. The extinction coefficient k and the refractive index n determined from the loss function Im(−1/e) by EELS were compared with the corresponding quantities calculated from DFT calculations. The UV absorption thresholds of these materials were determined by the electron excitation from the O 2p anionic band to the empty Ce 4f orbitals. The calculated and measured refractive indices were in satisfactory agreement. The applicability of CeO2, SrCeO3, and Sr2CeO4 as potential UV absorbers was assessed.