Transition Of Fe3 Research Articles

Evidence for clustering in iron-doped strontium titanate

Electron paramagnetic resonance spectra of iron-doped strontium titanate have been studied at room temperature for Fe concentrations between 0.2 and 1.0 mol%. The linewidth of the line associated with the 1/2 ↔ –1/2 transition of Fe3+ changes very little with with Fe concentration and the line intensity goes through a maximum between 0.40 and 0.60 mol%. The results suggest that the solid solution of Fe3+ in SrTiO3 is not random, but exhibits significant clustering effects.

Fe3+-doped broadband near-infrared phosphor with high quantum efficiency toward multifunctional pc-LEDs applications

A broadband near-infrared (NIR) luminescence that is comparable to chromium ions activated materials is fulfilled in Li3Sc2(PO4)3:Fe3+ phosphor, which is highly desired for environmental and biomedical applications due to the non-toxicity of Fe3+ ions. Structural and spectral analysis reveal that the broadband NIR emission peaked at 805 nm with a full width at half-maximum of 130 nm is derived from the non-selective two-site occupation of Fe3+ in the Sc3+ sites. A high internal/external quantum efficiency of 53 %/38.7 % is achieved via relaxing the selection rule for the forbidden 4T1(4G) → 6A1(6S) transitions of Fe3+ by larger lattice distortion. The influence of Fe3+ concentration and environment temperature on the broadband NIR luminescence properties of the as-prepared phosphors are also investigated. Finally, a NIR pc-LED prototype is fabricated and its electro-optical performance has guaranteed the applications in non-destructive detection and night vision. All the results have validated Li3Sc2(PO4)3 as a novel matrix system for access to highly efficient broadband NIR Fe3+-doping phosphor materials.

Highly active ZnO/Fe3+-TiO2 photocatalysts for visible-light photodegradation application and its colour change behaviour by d-d transition

Highly active novel ZnO/Fe-TiO2 composite catalysts with p-n junction heterostructure have been fabricated by adding commercial ZnO and sol–gel derived Fe-TiO2 nano-powders controlled by grinding and drying. This work reported that doped Fe (III) with TiO2 form a p-type semiconductor and whereas ZnO is an n-type semiconductor. The slight variation of electronegativity between ZnO and TiO2 causes a strong rectifying action for the formation of an interface between ZnO and Fe-TiO2. The occurrence of red shift phenomenon in absorption spectrum of the samples suggest the outcome of d-d transition of Fe3+ (2T2g → 2A2g, 2T1g) and the charge transfer transition between interacting Fe3+ ions (Fe3+ + Fe3+ → Fe4+ + Fe2+). These Fe3+ 3d states in addition to oxygen vacancies and Ti3+ centers create band states, thereby favouring the electronic transition to these levels and resulting in narrowing of TiO2 band gap. A direct confirmation is the increase of Urbach energy with the lowering in the band gap of ZnO/Fe-TiO2.The crystal field splitting of d orbitals (5 degenerate orbitals) of Fe3+ and the approach of free ligand ions which split into two sets and Fe3+ ligand field transition is discussed schematically. The photocatalytic activities of these heterostructure photocatalysts were evaluated by degrading toxic cationic organic dyes such as Methylene Blue (MB) and Malachite Green Oxalate (MG) under visible light. The mechanism of photocatalysis has been recommended which is based on the relative band structure of the semiconductor and integrated heterostructure. The formation of a spike barrier in the CB at the interface gives rise to trap sites that capture the migration of charge carriers and occurs recombination of electron-hole pair at higher Fe(III) doping concentration. The dark adsorption property of the catalysts sample has been also studied.

Physical and photo-electrochemical characterization of Ca2Fe2O5 for metronidazole antibiotic degradation under sunlight

This study aims to investigate and describe the properties of the brownmillerite Ca2Fe2O5, synthesized from nitrates precursors. The X-ray diffraction showed that the single phase crystallizes in an orthorhombic symmetry (Space Group: Pcmn) with a specific surface area of 8.16 m2 g−1. The d-d transition of Fe3+: in octahedral coordination gives a direct optical band gap (2.02 eV) as determined by diffuse reflectance spectroscopy in agreement with the brown color of the oxide. The first one is due to the charge transfer O2−: 2p → Fe3+: t2g. This enables the material to exploit a large part of the solar radiation for photocatalytic purposes. The chemical stability of Ca2Fe2O5 is demonstrated over the pH range (5–12). The capacitance-potential plot revealed n-type conduction; a flat band potential of (Efb) 0.40 VSCE and electron concentration (NA) of 8.57 × 1024 m−3 were obtained in Na2SO4 (0.1 M) solution. The intensity-potential (J - E) profile showed electrochemical stability with oxygen intercalation in the layered lattice. The conduction band is more anodic than the level of O2/O2•, allowing the successful oxidation of Metronidazole by •O2− radical under visible light. The photodegradation of Metronidazole (MNZ) was successfully achieved at an initial concentration of 10 mg/L under solar radiation and a photocatalyst dose of 1 g/L at a free pH after 120 min of exposure and obeys a first-order kinetic with a rate constant of (33.7 × 10−3 min−1).

Titanium-doped LiAlO2 ceramics for neutron scintillation

A series of bulk ceramic samples of titanium-doped LiAlO2 with doping concentrations of 0.05, 0.1, 0.5 and 1.0 at% were prepared using a sol-gel method. The LiAlO2:Ti samples showed emission in two spectral regions around 380 and 765 nm associated with the CT transition of Ti4+ and the d-d transition of Fe3+ impurities, respectively. The sample composition with 0.5 at% doping concentration exhibited the highest emission intensity. Furthermore, dense ceramic samples with 0.5 at% Ti-doping were prepared using spark plasma sintering. These samples exhibited intense CT luminescence of Ti4+ at 380 nm with a decay time of approximately 2.3 μs, while the emission of Fe3+ impurities was mostly suppressed.

One-step construction of bifunctional nanoprobes for NIR afterglow and T2-weighted MR imaging

In this study, spinel-phase Zn2Ga3-xFe3+xGe0.75O8 (x = 0, 0.002, 0.004, 0.02, 0.04, 0.08, 0.2) and Zn2Ga2.98-xFe3+xCr0.02Ge0.75O8 (x = 0, 0.0004, 0.001, 0.002 0.003, 0.004) nanoparticles were prepared by one-step hydrothermal method in combination with vacuum annealing. For ZGGO: Fe3+ nanoparticles, the near infrared (NIR) emissions (∼725 nm) originate from the 4T1(4G)→6A1(6S) transition of Fe3+ occupying octahedral and tetrahedral sites of Ga3+. Furthermore, their afterglow time is more than 15 min and Fe3+ doping will influence the generation of antisite defects pair (GaZn0−ZnGa′). For Cr3+ and Fe3+ co-doped ZGGO nanoparticles with average size of ∼46 nm, the NIR persistent luminescence around ∼700 nm, originating from the 2E→4A2 and 4T2→4A2 transitions of Cr3+, can be observed and the afterglow time exceeds 850 min. With the increase of Fe3+ concentration, the afterglow intensity decreases due to the decreased number of (GaZn0−ZnGa′) defects and deeper traps. In particular, autofluorescence-free imaging and MR imaging were successfully realized by using ZGGO: Cr3+, Fe3+0.002 nanoparticles dispersed in the simulated biological fluid environments (H2O, SLS and HSA). Their clear afterglow images can be acquired within 3 min after the stoppage of the UV irradiation and their transversal relaxivity (r2) is in the range of 227–140 mM−1s−1, which is close to the conventional Feridex T2 agent (108 mM−1s−1). Our results suggest that ZGGO: Cr3+, Fe3+ nanoprobes have potential applications in the diagnosis and therapy of disease.

Effects of Transition Metal Ions on the Colour of Blue-Green Beryl

This study reports the effects of transition metal ions on the colour of blue-green beryl. Industrial cameras were used to measure colour in the CIELAB colour space. X-ray fluorescence (XRF), X-ray diffraction (XRD), infrared spectroscopy (IR), and ultraviolet-visible (UV–vis) spectroscopy were used for characterization. The d–d transition of Fe3+ with sixfold coordination, the O2−→Fe3+ charge transfer, and the charge transition of binuclear metal M–M complexes formed by [Fe2(OH)4]2+ in the channel caused a yellow tone, whereas the charge transfer of Fe2+/Fe3+ with sixfold coordination caused a blue-green tone. The chroma of blue-green beryl was negatively correlated with the ratio of Cs+Mn to Fe contents. The lightness of blue-green beryl was negatively correlated with the total content of transition metal ions.

Field tuning magnetic phase transition in Dy0.5Tb0.5FeO3 single crystal

RFeO3 is an ideal candidate for the fabrication of spintronic devices, and its rare earth site doping is an important means to regulate and produce many unique spin behaviors. In this work, we report a high-quality Dy0.5Tb0.5FeO3 single crystal grown by optical floating zone method and its magnetic properties are studied explicitly. A type-Ⅱ spin switching effect and suppressed spin reorientation transition are found in the Magnetization vs Temperature curves in Dy0.5Tb0.5FeO3. In the temperature region of spin reorientation transition, the transition of Fe3+ magnetic sublattice configuration becomes very complicated by the influence of competitive interaction with magnetic Dy3+/Tb3+ ions. Interestingly, a field tunable double-hysteresis loop is observed near the antiferromagnetic transition temperature of rare earth ions sublattice, which has never been reported in RFeO3 family compounds. By studying the dependence of double-hysteresis loop at different temperatures, the magnetic phase transition and spin reorientation transition induced by the applied magnetic field are inferred. This novel physical phenomenon helps us understand the mechanism of spin configuration transition better at low temperatures.

Spectral properties and structure of transparent glass-ceramics based on Fe:MgAl2O4 and Fe:ZnAl2O4 crystals

Transparent glass-ceramics based on nanocrystals of magnesium aluminate and zinc aluminate spinels doped with iron ions have been obtained for the first time to our knowledge. The materials are promising for middle-IR spectral range laser technology. These materials are synthesized by heat-treating glasses of special composition in the temperature range of 720∘C−1050∘C . The glasses and glass-ceramics are studied by X-ray diffraction analysis and Raman and optical absorption spectroscopy. Their densities are measured, and differential scanning calorimetry data are obtained. It is shown that iron ions in glass-ceramics enter into tetrahedral and octahedral sites of crystals with a spinel structure. Increasing the heat-treatment temperature increases the absorption in the 2µm region originating from the 5E→5T2(5D) transition of Fe2+ ions in tetrahedral sites in spinel crystals.

Effect of heat-treatment mechanism on structural and electromechanical properties of eco-friendly (Bi, Ba)(Fe, Ti)O3 piezoceramics

Lead-free piezoelectric ceramics, (Bi0.70Ba0.35)(Fe0.65Ti0.35)O3 (BBFT), were fabricated via a solid-state reaction method and then treated using different heat-treatment processes (furnace cooling, air quenching (AQ), and water quenching). In all these ceramics, the X-ray diffraction analysis revealed morphotropic phase boundaries between the rhombohedral and tetragonal phases. Changes in the average grain size, relative density, and electrical properties in the BBFT–AQ composition were observed. For the optimum BBFT–AQ ceramic, significantly enhanced dynamic (d33* ~ 340 pm/V) and static (d33 ~ 165 pC/N) piezoelectric coefficients were obtained. Moreover, the d33* increased to 40% (d33* ~ 475 pm/V) with increasing temperature from 25 °C to 75 °C upon the application of a 4.0 kV/mm electric field. The related defect states were established by the variation in the transition of Fe3+ to Fe2+ and OV or $$V_{O}^{ \bullet \bullet }$$ concentration observed using X-ray photoelectron spectroscopy analysis. These factors are directly related to the electromechanical response enhancement in the BBFT piezoceramics. This study provides a paradigm for a deeper analysis of particular scientific heat-treatment mechanisms and the enhancement of functional properties in BBFT ceramics.

Synthesis, structure and spectroscopy of Fe2+:MgAl2O4 transparent ceramics and glass-ceramics

We report on a comparative study of a transparent Fe:MgAl2O4 (spinel) ceramics and a transparent nanophase Fe:MgAl2O4-based glass-ceramics. The 0.1 mol% Fe:MgAl2O4 ceramics was synthesized by hot pressing (at 1500 °C/50 MPa) of powders obtained by the sol-gel method using LiF as a sintering aid. The Fe:MgAl2O4 ceramic is a single-phase material (cubic structure, sp. gr. Fd3‾m, a = 8.083 Å) with a mean grain size of ~50 μm. The ceramic exhibits a broadband transparency of 0.2–6.0 μm and a high in-line transmission at ~1 μm of 74.4%. The iron ions are presented in the ceramics in the single state of Fe2+ species in tetrahedral (Td) sites. A broad absorption band spanning from ~1.2 to 3.7 μm assigned to the 5E → 5T2 (5D) transition of Fe2+ ions in Td sites is observed, corresponding to a ground-state absorption cross section of 0.28 × 10−18 cm2 at 1.90 μm. The glass-ceramics were prepared by secondary two-stage heat-treatments of the magnesium aluminosilicate glass nucleated by titanium oxide and doped with 0.1 mol% FeO. Transparent Fe:MgAl2O4-based glass-ceramics obtained at the temperature of the second stage of 800–1000 °C were multi-phase materials containing two crystalline nanophases, i.e., spinel (mean size: 3.7–7.4 nm) and magnesium aluminotitanate solid solution (mean size: 6.4–20.6 nm), as well as residual silica-rich glass. Glass-ceramics obtained at the temperature of the second stage of 1050 °C were transparent and based on Fe-doped sapphirine. For glass-ceramics, absorption has a much more complex character as it is caused by interplay of iron and titanium ions in different valence states, coordination sites and locations. The iron ions enter the spinel nanocrystals but unlike the ceramic, in the form of both VIFe2+ and IVFe2+ species. The developed ceramics and glass-ceramics are promising for saturable absorbers of mid-infrared (2–3 μm) lasers.

Influence of Fe2+ doping concentration on the structure and spectroscopic properties of transparent glass-ceramics based on Fe2+:ZnAl2O4 nanocrystals

Zinc aluminosilicate glasses nucleated by titanium dioxide, both undoped and doped with 0.6 and 1.0 wt% FeO were prepared by conventional melt-quenching technique and subsequently converted to glass-ceramics by controlled nucleation and crystallization in the temperature range of 720 – 1200 °C. The glasses and glass-ceramics were characterized by X-ray diffraction, Raman and optical spectroscopy. The addition of FeO speeds up the liquid phase separation of the initial glasses and gahnite (ZnAl2O4), rutile (TiO2) and cristobalite (SiO2) crystallization. Ferrous ions enter the gahnite crystals leading to a variation of the absorption spectra of glass-ceramics as compared to those of glasses. The glass-ceramics exhibit a broadband (1.5-2.5 μm) absorption due to the 5E → 5T2 (5D) transition of Fe2+ ions in tetrahedral sites in gahnite nanocrystals. They are promising as materials for gain media and saturable absorbers of mid-infrared lasers.

Spectral properties of novel transparent glass-ceramics based on Fe2+:ZnAl2O4 nanocrystals

Transparent glass-ceramics of the zinc aluminum silicate system nucleated by TiO2 and doped with FeO were developed by melt-quenching at 1580 °C with subsequent secondary heat-treatments at 720 – 1050 °C. The glass-ceramics based on nanosized gahnite crystals were characterized by X-ray diffraction, Raman and optical spectroscopy. The glass-ceramics exhibit a broad (1.5-2.5 μm) absorption due to the 5E → 5T2 (5D) transition of Fe2+ ions in Td sites in gahnite crystals. They are promising as saturable absorbers of the short-wave IR lasers.

Non-lanthanide activated red emission in CdAl2O4 phosphors with nanotube type crystal structure

Abstract Rare earth-doped phosphors have great potential in various applications. Given the cost issue confronting the rare earth ions, the doping of transition metal ions provides a cost-effective approach for realizing the light emitting. In this paper, using CdAl2O4 as the host, red emission through Fe3+ ions has been demonstrated. CdAl2O4:Fe3+ shows the strong red emission at around 700 nm, attributing to the 4T1(4G) to 6A1(6S) transitions of Fe3+ ions. Moreover, the intensity dependence of such a red emission on the Fe3+ doping is quantitatively analyzed, and the optimized doping concentration is 0.015. Band structure calculation indicates that Fe3+ doping can widen the light absorption range of CdAl2O4 host via doping the Fe3+ ions. The efficient luminescence can be elucidated by the synergistic effect of electrons in Fe3+ ions and nanotube-type host lattice. Furthermore, on the basis of these findings, we developed Cr3+-doped red emission phosphors. Moreover, a red LED is successfully fabricated via combination Cr3+-doped CdAl2O4 phosphors with near UV LED ships. The successful realization of red lighting via Fe3+ or Cr3+ ions provides a new perspective for the development of luminescent materials, thereby initiating the non-rare-earth based phosphors for light emitting diodes and displays applications.

Synthesis, structure and spectroscopy of Fe2+:MgAl2O4 transparent ceramics

Transparent ceramics based on magnesium aluminium spinel, MgAl2O4, doped with iron ions (Fe2+) are synthesized by hot pressing (at 1500 °C / 50 MPa) of powders obtained by the sol-gel method. The ceramics are characterized by X-ray diffraction, SEM, Raman and optical spectroscopy. The ceramics exhibit a broad (1.3-3.5 μm) absorption due to the 5E → 5T2 (5D) transition of Fe2+ ions in Td sites and they are promising for applications as saturable absorbers of mid-infrared lasers.

The photocatalytic hydrogen formation and NO2− oxidation on the hetero-junction Ag/NiFe2O4 prepared by chemical route

The photoelectrochemical ability of Ag(5%)/NiFe2O4 for H2 evolution under visible light irradiation was studied. The hetero-junction prepared by sol gel method shows a much higher activity than the physical mixture (hetero-system: Ag + NiFe2O4). The electrons of NiFe2O4 activated by visible light are focalized toward Ag clusters, intimately contacted to the spinel. The bifunctional crystallite is generated by incorporation of ultrafine Ag crystallites, thereby avoiding high over-voltages. The spinel was characterized by thermal analysis, X-ray diffraction and scanning electron microscopy. The optical gap of NiFe2O4 (1.59 eV) is due to the crystal field splitting of d-d transition of Fe3+: 3d orbital in octahedral site. p-type conductivity of NiFe2O4 was demonstrated from the capacitance measurement in alkaline KOH solution (0.1 M). The conduction band (−0.87 V) is more cathodic than the H2 evolution and the hetero-junction was successfully used for the photochemical hydrogen production under visible light irradiation. The photo-activity is dependent on the nature of the hole scavenger (NO2−, Fe(CN)64− and I−). NO2− is a hazardous ion and gave the best activity, due to its optimal band bending of 0.5 V and is converted to nitrate. An evolution rate of {0.17 cm3 H2 (g catalyst)−1 mn−1} was obtained at pH ∼ 7 with an apparent quantum yield of 1.3%.

SrAl12O19: Fe3+ @3‐aminopropyl triethoxysilane: Ambient aqueous stable near‐infrared persistent luminescent nanocomposites

AbstractNear‐infrared (NIR) persistent luminescent nanoparticles (N‐PLNPs) endow a long‐term in vivo imaging with deep tissue penetration and high signal to noise ratio. However, synthesis route and applicable afterglow center for N‐PLNPs are still limited. Here, we report on a new synthesis by employing chemical precipitation as the central pivot, which is simpler and has controllable and reproducible routes than the existing technique. We also introduce Fe3+ ion as a new member to join the group of afterglow emitters. Although its NIR luminescence is ubiquitous, its NIR afterglow is still almost never reported. In this paper, SrAl12O19: Fe3+ N‐PLNPs display a NIR persistent luminescence from 750 to 1000 nm, which is assigned to 4T1(4G)→6A1(6S) transition of Fe3+. Furthermore, a surface‐amination technique is proposed to improve the stability of SrAl12O19: Fe3+ N‐PLNPs in aqueous solution. After encapsulating the N‐PLNPs with 3‐aminopropyl triethoxysilane (APTES), SrAl12O19: Fe3+ @APTES nanocomposites exhibit a hydrophilic stability beyond 20 days in aqueous solution. The results make them valuable in studying the biological functions of biomolecules and monitoring cellular networks in their native contexts.

Time-resolved spectroscopy of Fe3+d-d transition in bulk ZnSe polycrystal

We report temperature dependent time-resolved photoluminescence studies of Fe3+ in ZnSe polycrystals over 10–300 K temperature ranges fabricated by the post growth thermal diffusion technique. The d-d transitions of Fe3+ assigned to the 4T2(G)→6A1(S) and 4T1(G)→6A1(S) transitions are clearly identified at 528 and 627 nm, respectively, at 10 K. The observed emission peaks in the near bandgap region are red-shifted from 439 to 463 nm as the temperature increases, resulting in a temperature coefficient of 10.21×10−4 eV/K and Debye temperature = 336 K fitted by the Varshni equation. The radiative lifetime at 528 nm by time-resolved photoluminescence is evaluated as τrad = 774 ± 4 ps, activation energy (ΔEa) = 717.2 cm−1, and relaxation time rate (1/W0) = 3.1 ps.

Calculation of the electronic and optical properties of LiFe5O8: An ab initio study

Ab initio calculations based on density functional theory have been employed to study electronic and optical properties of lithium ferrite spinel (LiFe5O8, LFO) based on density functional theory. The calculated of structural properties are in a good agreement with previously reported experimental results. The calculated band gap is indirect with a value of 2.3 eV, which overestimated the experimental value of 1.9 eV. The top of the valence band and the bottom of the conduction band of the LFO are dominated by the 3d states of Fe3+(1) (8c site) and Fe3+(2) (12d site). The magnetic moment calculated for the ion of Fe3+ 12d site was 3.90 μβ and 3.1 μβ for the 8c site. The electron transitions that generate the absorption edge of the compound are characterized by d-d transitions of Fe3+(1,2) at 12d and 8c sites, which agree with the experimental. The calculated value of the static dielectric constant (ω → 0), obtained from calculation of refractive index, is 1.66.

Novel Single-Crystal Hollandite K1.46Fe0.8Ti7.2O16 Microrods: Synthesis, Double Absorption, and Magnetism.

Novel multifeatured hollandite K1.46Fe0.8Ti7.2O16 (KFTO) was synthesized by a simple hydrothermal method. Magnetic KFTO microrods were well controlled to long rectangular rods with pyramid-shaped tops. A KFTO growth mechanism was proposed on the basis of examining phase and morphology of the samples acquired at different reaction times. The KFTO morphology was confirmed by the calculated surface energies. The UV-vis diffuse reflectance spectra of KFTO microrods showed double absorption with band gaps of 2.01 and 2.16 eV, which was further confirmed by photoluminescence. First-principles studies revealed that the double absorption and magnetic properties originate from the d-d transitions of Fe3+ under the crystal field. The magnetic property could be applied in ferromagnetic semiconductor devices and the double absorption could be applied in visible-light harvesting. This work highlights the multifunctional KFTO microrods with low cost and environmental friendliness.