Fabrication and properties of transparent Tb:YAG fluorescent ceramics with different doping concentrations

Terbium doped yttrium aluminum garnet (Tb:YAG) transparent ceramics with different doping concentrations were fabricated by the solid-state reaction method using commercial Y₂O₃, α-Al₂O₃ and Tb₄O₇ powders as raw materials. Samples sintered at 1750 °C for 20 h were utilized to observe the optical transmittance, microstructure and fluorescence characteristics. It is found that all the Tb: YAG ceramics with different doping concentrations exhibit homogeneous structures with grain size distributions around 22–29 µm. For the 5 at% Tb:YAG transparent ceramics, the grain boundaries are clean with no secondary phases. The photoluminescence spectra show that Tb:YAG ceramics emit predominantly at 544 nm originated from the energy levels transition of ⁵D₄→⁷F₅ of Tb³⁺ ions, and the intensity of the emission peak reaches a maximum value when the Tb³⁺ concentration is 5 at%. The in-line transmittance of the 5 at% Tb:YAG ceramics is 73.4% at the wavelength of 544 nm, which needs to be further enhanced by optimizing the fabrication process. We think that Tb:YAG transparent ceramics may have potential applications in the high-power white LEDs.     

Highly efficient photocatalytic activity and mechanism of novel Er3+ and Tb3+ co-doped BiOBr/ g-C3N5 towards sulfamethoxazole degradation

Bismuth oxyhalides (BiOX (X = Cl, Br, I) are considered to be an important p-type semiconductors in the photocatalysis applications. In particular, tetragonal BiOBr is considered as a stable photocatalyst due to its resilient absorption in the visible region with an band gap energy of 2.8 eV. In the meantime, lanthanide ions (with 3+ oxidation state) implies as conversion catalyst gained huge impact and remain a serious topic in materials chemistry. Here we synthesized upconversion photocatalyst mainly consists of BiOBr with the Er ³⁺ and Tb ³⁺ ions along with low band gap g-C₃N₅ for the improved photocatalytic performances. The synthesized Er³⁺/Tb³⁺@BiOBr-g-C₃N₅ heterojunction was systematically characterized by XRD, and FT-IR for the confirmation of the composite and their morphology were analysed with FESEM and HR-TEM analysis which revealed that the sheets of g-C₃N₅ were decorated by Er³⁺/Tb³⁺ loaded BiOBr microspheres. The XPS analysis confirmed the suitable oxidation state of all the individual elements existing in the composite. As the UV-DRS analysis showed that the band gap of the Er³⁺/Tb³⁺ BiOBr-gC₃N₅ heterojunction was narrowed to 2.64 eV. To evaluate the photocatalytic efficiency of the synthesized g-C₃N₅, Er³⁺/Tb³⁺@BiOBr and Er³⁺/Tb³⁺@BiOBr-gC₃N₅ heterojunction under the simulated visible light irradiation source towards the aqueous sulfamethoxazole degradation. The Er³⁺/Tb³⁺@BiOBr-gC₃N₅ heterojunction shows maximum degradation efficiency of 94.2% after 60 min of visible light irradiation whereas the pure g-C₃N₅ provided about 43.8% and Er³⁺/Tb³⁺@BiOBr implies 55.2% degradation efficiency. The plausible degradation mechanism of pollutant removal was proposed.     

Photoluminescence Properties of Color‐Tunable Ca3La6(SiO4)6: Ce3+, Tb3+ Phosphors

A series of newly developed color‐tunable Ca₃La₆(SiO₄)₆: Ce³⁺, Tb³⁺ phosphors were successfully prepared in this study. The crystal structures of the prepared phosphors were revealed to be hexagonal with space group P6₃/m, and the lattice parameters were evaluated via utilizing the Rietveld refinement method. Upon excitation at 288 nm, the emission spectra of Ce³⁺and Tb³⁺ ions co‐doped Ca₃La₆(SiO₄)₆ phosphors included a blue emission band and several emission lines. The blue emission band with a peak at 420 nm originated in the f–d transitions of Ce³⁺ ions, and the emission lines in the range of 450–650 nm were assigned to the ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions. Increasing the doping content of Tb³⁺ ions considerably strengthened Tb³⁺ emission and reduced Ce³⁺ emission owing to the energy transfer from Ce³⁺ to Tb³⁺ ions. The mechanism of the energy transfer was confirmed to be a dipole–dipole interaction. The effective energy transfer from Ce³⁺ to Tb³⁺ ions caused a color shift from purplish‐blue to yellowish‐green. Color‐tunable Ca₃La₆(SiO₄)₆: Ce³⁺, Tb³⁺ phosphors have the potential to be utilized in light‐emitting diodes with proper modulation of the amount of Tb³⁺ ions.     

Effects of rare-earth oxide doping on the thermal radiation performance of HfO2 coating

In this study, the REO-HfO₂ (REO = Tb₄O₇, Gd₂O₃ and Sm₂O₃) coatings and pure HfO₂ coatings were prepared by atmospheric plasma spraying. The chemical compositions, morphologies, infrared radiation performance and thermal resistances of the coatings were systematically investigated. The experimental results showed that the Tb₄O₇-HfO₂, Gd₂O₃-HfO₂, Sm₂O₃-HfO₂ and pure HfO₂ coatings had infrared emissivity values of 0.863, 0.852, 0.854 and 0.621, respectively, at room temperature. Based on the phase analysis, the higher infrared emissivity of the REO-HfO₂ coatings could be attributed to the fact that the newly formed RE₂Hf₂O₇ (RE = Tb, Gd and Sm) phase, which had a defective fluorite-type structure, and the RE³⁺ ions enhanced the lattice absorption and electron absorption. Additionally, the Tb₄O₇-HfO₂ coating exhibited a relatively higher infrared emissivity than those of the Gd₂O₃-HfO₂ and Sm₂O₃-HfO₂ coating over the wavelength range of 1–15 μm, which was due to the relatively higher vibrational frequency of the TbO bond in RE₂Hf₂O₇ (RE = Tb, Gd and Sm) and the transformation of Tb³⁺ into Tb⁴⁺ in the Tb₄O₇-HfO₂ system. In addition, the REO-HfO₂ ceramic coatings exhibited excellent thermal resistance, which could withstand high-temperature treatment at 1600 °C for at least 50 h without undergoing a phase change and exfoliation, and the infrared emissivity at different temperatures hardly changed after thermal treatment.     

Studies of dielectric properties of rare earth (Dy,Tb, Eu) doped barium titanate sintered in pure nitrogen

This paper investigated dielectric properties of rare earth (Dy, Tb, Eu)-doped barium titanate sintered in pure nitrogen. The substituting concentration of rare earth (Dy, Tb, Eu) was 2.0 mol%. The doping behaviors of intermediate rare-earth ions (Dy, Tb, Eu) and their effects on the dielectric property of barium titanate were investigated. Eu³⁺ ion was substituted in the A-site of the perovskite lattice. Dy³⁺ and Tb³⁺ ions substituted partially for Ti⁴⁺ site and partially for Ba²⁺ site. The different rare earth element had a crucial effect on dielectric properties of rare-earth-doped BaTiO₃. Among these doped samples, Tb-doped BaTiO₃ had the largest dielectric constant (70,000–80,000); the smallest dielectric loss (less than 4%), and good capacitance-temperature coefficient, which satisfies the X7R specification of the Electronic Industries Association Standards (TCC within ±15% from ?55 °C to 125 °C).     

Mixed-valent structure,dielectric properties and defect chemistry of Ca1−3x/2TbxCu3Ti4−xTbxO12 ceramics

Single-phase Ca_1−3x/2Tb_xCu₃Ti_4−xTb_xO₁₂ (0.025≤ x≤0.075) (CTCTT) ceramics with a cubic perovskite-like structure and a fine-grained microstructure (1.6‒2.3 µm) were prepared using a mixed oxides method. The results revealed that mixed valence states of Cu²⁺/Cu⁺, Ti⁴⁺/Ti³⁺, and Tb³⁺/Tb⁴⁺ coexisted in CTCTT. A multiphonon phenomenon in the Raman scattering at 1148, 1323, and 1502 cm⁻¹ was reported for undoped and doped CTTO. Tb was mainly incorporated in the interior of the CTCTT grains rather than on the surface. The dielectric permittivity of CTCTT (ε_r'_RT =3590‒5200) decreased relative to CCTO (ε_r'_RT =10240) at f =1 kHz, but the dielectric loss of CTCTT (the minimum value of tan δ=0.12 at RT) increased as a result of Tb doping. The defect chemistry of CTCTT is discussed. The internal barrier layers capacitance (IBLC) model was adopted for impedance spectroscopy (IS) analysis. The activation energies of the grain boundaries (E_gb) and semi-conductive grains (E_g) for CTCTT were determined to be 0.52 eV and 104 meV, respectively. The IS and defect chemistry analyses confirmed that the decrease in the dielectric permittivity was mainly due to a decrease in conductivity in the semiconducting CTCTT grains caused by the acceptor effect of Tb⁴⁺ at the Ti site, which resulted in a decrease in the IBLC effect.     

Broadband excited Na3Tb(PO4)2:Ce3+/Eu2+ green/yellow-emitting phosphors with high color purity for LED-based application

To enhance the display quality of light-emitting diodes (LEDs), it is of great significance to exploit green/yellow-emitting phosphors with narrow emission band, high quantum yield, and excellent color purity to satisfy the application. Herein, orthophosphate-based green/yellow-emitting Na₃Tb(PO₄)₂:Ce³⁺/Eu²⁺ (NTPO:Ce³⁺/Eu²⁺) phosphors have been successfully synthesized by a facile solid-state reaction method. The absorption band of NTPO samples was extended to the near-ultraviolet region and the absorption efficiency was significantly improved owing to a highly efficient energy transfer from Ce³⁺/Eu²⁺ ion to Tb³⁺ ion in NTPO host certified by time-resolved PL spectra. Upon 300 nm excitation, the NTPO:Ce³⁺ is characterized by ultra-narrow-band green emission of Tb³⁺ with an absolute quantum yield of 94.5%. Unexpectedly, NTPO:Eu²⁺ emits bright yellow light with a color purity of 73% as a result of the blending of green light emission from Tb³⁺ and red light emission from Eu³⁺. The thermal stability has been improved by controlling the stoichiometric ratio of Na⁺. The prototype white LED used yellow-emitting NTPO:Eu²⁺ phosphor has higher color-rendering index (Ra = 83.5), lower correlated color temperature (CCT = 5206 K), and closer CIE color coordinates (0.338, 0.3187) to the standard white point at (0.333, 0.333) than that used green-emitting NTPO:Ce³⁺ phosphor, indicating the addition of the yellow light component improved the Ra of the trichromatic (RGB) materials.     

Visible emission and energy transfer in Tb3+/Dy3+ co-doped phosphate glasses

In this work, we systematically study the spectroscopic properties of Tb³⁺/Dy³⁺ co-doped phosphate glasses in the visible spectral region and explore the sensitization role of Dy³⁺ in the enhancement of visible fluorescence of Tb³⁺ ions. Judd-Ofelt parameters Ω₂ and Ω₄/Ω₆ of the phosphate glass as host for Tb³⁺ are calculated as 21.60 × 10^-20 cm² and 0.73, respectively, based on the measured spectral absorption. Multiple energy transfer (ET) routes from Dy³⁺ to Tb³⁺ and their efficiencies are characterized, and the enhanced fluorescence properties of Tb³⁺ are investigated, including the emission spectral strength and the spontaneous emission lifetime as functions of Dy³⁺ doping concentration. The efficient nonradiative ET processes between Dy³⁺ and Tb³⁺ allow a moderate concentration level of Tb³⁺ to achieve favorably stronger spectral absorption at blue and ultraviolet wavelengths. Tb³⁺/Dy³⁺ co-doped phosphate glass shows promising potential for phosphors and lasing operation at visible wavelengths.     

Visible Quantum Cutting and Energy Transfer in Tb3+‐Doped KSr(Gd,Y)(PO4)2 Under VUV–UV Excitation

KSr(Gd,Y)(PO₄)₂: Tb³⁺ phosphors were synthesized using the high‐temperature solid‐state reaction method. The VUV–UV spectroscopic properties of these phosphors were studied. The results show that efficient energy transfer (ET) from Gd³⁺ to Tb³⁺ occurs in this system, and the ET efficiency increases with increasing of Tb³⁺ doping concentrations, which is evidenced that both the emission intensity and decay time of Gd³⁺ decreases with increasing Tb³⁺ doping concentrations. Visible quantum cutting via cross relaxation between the neighboring Tb³⁺ ions was observed in the high Tb³⁺ concentration doped sample. In addition, the emission color of KSr(Gd,Y)(PO₄)₂: Tb³⁺ phosphors can be tuned from blue to yellowish‐green by varying the doping concentration of Tb³⁺. Under 147 nm excitation, the sample KSrGd_0.5(PO₄)₂: 0.5Tb³⁺ exhibits the strongest emission, which is about 70% of the commercial green‐emitting phosphor Zn₂SiO₄: Mn²⁺ indicating the potential application of this phosphor for plasma display panels, Hg‐free lamps, and three‐dimensional displays.     

NaBaY(BO3)2:Ce3+,Tb3+: A novel sharp green‐emitting phosphor used for WLED and FEDs

A new borate phosphor NaBaY(BO₃)₂: Ce³⁺, Tb³⁺ (NBY:Ce³⁺, Tb³⁺) was successfully synthesized under low temperature designed to put into application in the fields of ultraviolet (UV)‐excited light emitting diodes (LEDs) and field emission displays (FEDs). The structure distortion between Ce³⁺, Tb³⁺ single‐ and co‐doping NBY was discussed by X‐ray powder diffraction Rietveld refinement, high‐resolution transmission electron microscopy (HRTEM) and spectra. NBY: Ce³⁺, Tb³⁺ presents a wide absorption band ranging from 310 to 400 nm and efficient green emission (λ_max = 542 nm) with a full‐width at half‐maximum of 3.3 nm. The remarkable thermal stability has also been tested, indicating that the intensity at 200°C is still beyond 70% of the original intensity. In addition, a white LED device was manufactured by connecting a 370 nm UV chip with a blend of BaMaAl₁₀O₁₇: Eu²⁺ (BAM: Eu²⁺), NBY: Ce³⁺, Tb³⁺ and CaAlSiN₃: Eu²⁺. The color coordinate, correlated color temperature and color rendering index of the manufactured LED device were (0.335, 0.347), 5511 K and 80.16, respectively. Meanwhile, the cathodoluminescence (CL) spectra under the various conditions of probe currents and accelerating voltages were also analyzed. Through successive excitation of low‐voltage electron‐beam, the wonderful performances of degradation property and color stability were obtained. These results suggest that the green‐emitting NBY: Ce³⁺, Tb³⁺ phosphor has the prospect of becoming applications in white UV LEDs and FEDs.     

Band gap and oxygen vacancy engineering of honeycomb-like CuFe2O4 spinels toward enhanced high infrared emissivity

Recently, copper ferrites have acquired widespread attraction in high infrared radiation fields owing to their remarkable cost efficiency. However, to achieve broader applications under various operating conditions, it is essential to further improve the infrared emissivity, particularly at high temperatures. Herein, the Ni-doped CuFe₂O₄ (NCFO) honeycomb-like frameworks, which are constructed with single-crystal nano-subunits, are successfully fabricated via the scalable sol–gel avenue. The unique porous honeycomb framework endows NCFO with enhanced infrared absorption and relieves the stress between coatings and substrates meanwhile. With both band gap and oxygen vacancy (OV) engineering of CuFe₂O₄ itself via smart Ni doping, a maximum lattice strain, the richest OVs, and the narrowest band gap (∼1.63 eV) are simultaneously achieved for the CuFe₂O₄ with 15% Ni doping (denoted as CNFO-15). Benefiting from the synergy of these external and intrinsic contributions, the CNFO-15 possesses an ultrahigh infrared emissivity (∼0.975) in the wavelength range of 3–5 µm at a test temperature of 800°C. Moreover, the CNFO-15-based coating displays superior infrared radiation performance with outstanding high-temperature resistance. More meaningfully, the constructive design here will provide a distinctive perspective for future large-scale fabrication of advanced high-infrared-emissivity coatings.     

Infrared radiation performance and calculation of B-site doped lanthanum aluminate from first principles

Pure LaAlO₃ and LaAl_1-xNi_xO₃ samples (x?=?0.05, 0.1, 0.15, 0.2, 0.25, 0.3) were prepared using a sol-gel technique. The samples were analyzed and characterized using XRD, SEM, FT-IR and XPS. The results showed that the infrared emissivity of LaAl_1-xNi_xO₃ powder prepared at 1500?℃ for 2?h increases with Ni²⁺ doping content. For x?=?0.25, the mean emissivity in the 3–5?µm infrared spectral region was 0.835. This was a 142% increase compared with that of pure LaAlO₃ (0.345). The doped Ni ions mainly exist with valences of +?2 and +?3 in the LaAlO₃ lattice. After doping, the concentration of electron holes and oxygen vacancies increased, leading to an enhancement of free carrier absorption in the system. It indicated that the Ni²⁺ doping would introduce an impurity energy level in the forbidden band of LaAlO₃ by first principles calculation, forming primarily by the hybridization of the 3d orbital electrons of the Ni ions and the 2p orbital electrons of the oxygen atoms. When x?=?0.25, the band gap decreased from 3.50?eV to 0.77?eV. The impurity energy level allows for a reduction in the energy required for the electrons transferring from the valence band to the conduction band, causing increased numbers of electron transitions between the band gaps, thus enhancing free carrier absorption and increasing the infrared emissivity of the material. The LaAl_1-xNi_xO₃ oxide materials prepared in this work had excellent infrared radiation properties. As a lining material at high temperature reacting furnace, the energy loss could be reduced, the heat utilization efficiency would be greatly improved, and the utility model could be used in the field of high-temperature thermal energy saving.     

Comprehensive study on structural,thermal, morphological and luminescence (RL,PL, TL) properties of CaLa2(WO4)4: Tb3+, Dy3+ phosphors synthesized via sol-gel method

Tb³⁺/Dy³⁺ co-doped CaLa₂(WO₄)₄ (CLW: Tb³⁺/Dy³⁺) and its derivatives were synthesized by the sol-gel method. The morphology, thermal, structure and luminescent-optical properties the as-prepared light-emitting phosphors were characterized by utilizing scanning electron microscopy (SEM), differential thermal analysis (DTA)-thermogravimetric analysis (TG), X-ray diffraction (XRD) and radioluminescence (RL or X-ray luminescence) - photoluminescence (PL) –thermoluminescence (TL or TSL) - optical absorption spectrometry. The Tb³⁺ and Dy³⁺ ions were singly or doubly doped and the results were examined in detail. Moreover, for these phosphors, the energy transfer mechanisms which depend on RL and PL spectra were determined. The samples excited by X-ray demonstrate characteristic luminescence peaks of Dy³⁺ (422, 480, 575, 663 and 747 nm) and Tb³⁺ (489, 544, 586, 620, 652 and 675 nm). These emissions are similar for RL and PL measurements. It could be said that the energy transfer efficiency of the host material is perfect for rare-earth ions. The synthesized phosphors exhibit various colors from yellow to blue under UV excitation. The optical band gaps of host CLW, CLW: Tb³⁺, CLW: Dy³⁺ and co-doped CLW: Tb³⁺/Dy³⁺ were calculated at values 3.83 eV, 3.44 eV, 3.64 eV and 3.52 eV, respectively. From the results obtained, the CaLa₂(WO₄)₄: Tb³⁺, Dy³⁺phosphors may be one of the potential candidates for light-emitting diode.     

Precipitation Synthesis and Color‐Tailorable Luminescence of α‐Zr(HPO4)2: RE3+(RE = Eu,Tb) Nanosheet Phosphors

The rare earth (RE = Eu and Tb) ions‐doped α‐Zr(HPO₄)₂ (ZrP) nanosheet phosphors were synthesized by direct precipitation method, and their structures and photoluminescence properties were investigated. The results of X‐ray diffraction and scanning electron microscopy indicated that the systems of ZrP:RE³⁺ had similar nanosheet structure except with relatively larger interlayer spacing as compared with pure α‐ZrP. Under the excitation of UV light, the ZrP:RE³⁺ nanosheet phosphors showed red and green emission peaks corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ and the ⁵D₄→⁷F₅ transition of Tb³⁺, respectively. After Eu³⁺ and Tb³⁺ were co‐doped in ZrP host, not only the red and green emission peaks were simultaneously observed, but also the luminescent intensity and fluorescence lifetimes of Tb³⁺ were gradually decreased with the increase in Eu³⁺‐doping concentration, which implied the energy transfer from Tb³⁺ to Eu³⁺ happened. It was deduced that the energy transfer from Tb³⁺ to Eu³⁺ occurred via exchange interaction. Through optimization to the samples, a nearly white‐light emission with the color coordinate (0.322, 0.263) was achieved under 377 nm excitation. The ZrP:RE³⁺ nanosheet phosphors may be a potential color‐tailorable candidate for fabricating optoelectronic devices such as electroluminescence panels.     

A novel tunable green-to-red emitting phosphor Ca4LaO(BO3)3:Tb,Eu via energy transfer with high quantum yield

A novel green phosphor composed of Ca₄LaO(BO₃)₃:Tb³⁺ (CLBO:Tb) has been synthesized by a combustion method with urea. Its crystal structure, temperature-dependent luminescence, and quantum yield (QY) have been characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra with heating device and integrate sphere. No concentration quenching has been observed when all of La³⁺ ions are substituted with Tb³⁺ ions. Green phosphor Ca₄TbO(BO₃)₃ (CTBO) has 200% luminescence intensity of commercially available phosphor LaPO₄:Ce, Tb (LPO:Ce, Tb) under 378 nm excitation. The QY of CTBO is as high as 98%. Through a Dexter energy transfer mechanism, Eu³⁺ ions are efficiently sensitized by Tb³⁺, resulting in an emission with color tunable from green to red under ultraviolet excitation. A possible mechanism of energy transfer from Tb³⁺ to Eu³⁺ has been investigated by PL spectra and decay measurements. The energy transfer efficiency from Tb³⁺ to Eu³⁺ increases linearly with concentration of Eu³⁺ increasing.     

Optical Performances of YAG:Re3+ (Re = Ce,Eu) Phosphor Films with Co‐Doping Tb3+ as Energy‐Transfer Sensitizer

The paper investigates the effect of co‐doping Tb³⁺ as an energy‐transfer sensitizer on optical properties of YAG:Re³⁺ (where, Re = Ce, Eu) phosphor films synthesized by sol–gel route. The results suggest that, Tb³⁺ is a promising sensitizer for improving the optical performances of the as‐prepared YAG:Re³⁺ films, and a Tb³⁺ co‐doping concentration of 20% was found to be an optimum level on account of Tb³⁺ concentration quenching. Due to the energy‐transfer processes of Tb³⁺→Re³⁺, the as‐prepared Y_0.8 Tb_0.2AG:Re³⁺ films displayed strong abilities of absorption in the ultraviolet (UV) light range, and bright green–yellow emission for YAG:Ce³⁺ or red emission for YAG:Eu³⁺ under 275 nm irradiation, which could be utilized for UV‐excited WLED and display applications.     

Size controllable synthesis and multicolor fluorescence of SiO2:Ln3+(Ln=Eu,Tb) spherical nanoparticles

A series of size controllable Tb³⁺ and/or Eu³⁺ activated nano-sized silica phosphors have been successfully synthesized through a facile sol-gel method. The structure, morphology, compositions, and luminescence properties of as-prepared samples were well investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) and photoluminescence spectroscopy (PL). The results showed that all as-prepared samples were spherical nanoparticles but the sizes reduced gradually with the temperature increased from 25 °C to 65 °C, which was contrary to the BET surfaces as well as the luminescence intensity. Under ultraviolet excitation, the SiO₂:Ln³⁺(Ln=Eu, Tb) spherical nanoparticles showed characteristic red and green emissions corresponding to f-f transition of Eu³⁺ and Tb³⁺, respectively. Moreover, the luminescence emissions of samples can be tuned from green to yellow, orange and red by co-doping the Tb³⁺ and Eu³⁺ ions in different concentration ratio into the SiO₂ host due to the efficient dipole–dipole energy transfer mechanism from Tb³⁺ to Eu³⁺ under 377 nm excitation. These results show that as-prepared phosphors may find potential applications in color display fields.     

Enhancement in CO oxidation activity of nanosized CexZr1−xO2 solid solutions by incorporation of additional dopants

The influence of Hf, Pr and Tb dopant cations on structural and catalytic properties of nanosized Ce_xZr_1?xO₂ solid solutions has been investigated. A wide range of analytical techniques are utilized to characterize the synthesized materials, and the catalytic activity is evaluated for CO oxidation. XRD, Raman, SEM and TEM results suggested formation of dopant cation incorporated ceria–zirconia solid solutions with highly homogeneous morphology and lattice defects. The CO-TPR measurements revealed an enhanced reducibility of Ce_xZr_1?xO₂ which is reflected in their better catalytic activity. The role of Tb⁴⁺/Tb³⁺ and Pr⁴⁺/Pr³⁺ redox couples in facilitating a higher activity has been addressed.     

A Kinetic study of Tb3+ and Dy3+ co-substituted CoFe2O4 spinel ferrites using temperature dependent XRD,XPS and SQUID measurements

In this research work, we have investigated the structural development of Tb³⁺ and Dy³⁺ co-substituted CoFe₂O₄ ferrites using temperature and time dependent XRD measurements. Sol-gel auto combustion technique was used to synthesized Tb³⁺ and Dy³⁺ co-substituted spinel ferrites with composition CoFe_2-x-y Tb_xDy_yO₄ (x + y = 0.0–0.25). Various characterization techniques such as High temperature XRD, XPS and SQUID were used to observe the Kinetics mechanism as well as the impact of co-substitution on the structural and magnetic properties. Room temperature XRD scans showed that the synthesized materials having single phase and were crystalline in nature. The crystallite size was lied in nano regime ranging from 26.07 to 21.92 nm and lattice parameters were found to be decreased with increasing rare earth metal ions contents. Temperature and time dependent XRD data suggested that structure of investigated samples not degrade even at temperature 900 °C which was maintained for 2 h. The ionic states of Co²⁺, Tb³⁺, Dy³⁺ and Fe³⁺ were confirmed by X-ray Photoelectron spectrometry measurements along with the binding energies of Co2p, Tb 2p, Dy 2p, Fe 2p which confirmed the tetrahedral and octahedral sites for substituted ions. Room temperature magnetic measurements of annealed nanoferrites were carried out by operating the SQUID magnetometer in VSM mode. The data demonstrated that increasing concentrations of substituent (Tb³⁺and Dy³⁺) resulted in the reduction of various magnetic parameters such as remanence, saturation magnetization and Coercivity. The calculated values of saturation magnetization and coercivities were found in the range of 78.1–45.15emu/g and 742–543Oe respectively. This study concluded that cation distribution and crystallite size is effective in controlling the structural, morphological and magnetic properties.     

Extremely Enhanced Nonlinear Current–Voltage Properties of Tb‐Doped CaCu3Ti4O12 Ceramics

Nonlinear current–voltage properties of CaCu₃Ti₄O₁₂ ceramics were extremely enhanced by doping with Tb. Substitution of Tb to CaCu₃Ti₄O₁₂ resulted in a decrease in grain size due to the ability of Tb ions to inhibit grain boundary mobility. The dielectric properties of CaCu₃Ti₄O₁₂ ceramics were degraded after doping with Tb. Surprisingly, the nonlinear electrical properties were strongly enhanced. The best properties with a nonlinear coefficient of ~29.67 and breakdown electric field strength of ~1.52 × 10⁴ V/cm were obtained in the Ca_0.775Tb_0.15Cu₃Ti₄O₁₂ ceramic. These extremely enhanced properties were attributed to modification of grain boundary electrical response due to the effect Tb substitution.