Perovskite Host Research Articles

Concurrent Amorphization and Nanocatalyst Formation in Cu-Substituted Perovskite Oxide Surface: Effects on Oxygen Reduction Reaction at Elevated Temperatures.

The activity and durability of chemical/electrochemical catalysts are significantly influenced by their surface environments, highlighting the importance of thoroughly examining the catalyst surface. Here, Cu-substituted La0.6Sr0.4Co0.2Fe0.8O3-δ is selected, a state-of-the-art material for oxygen reduction reaction (ORR), to explore the real-time evolution of surface morphology and chemistry under a reducing atmosphere at elevated temperatures. Remarkably, in a pioneering observation, it is discovered that the perovskite surface starts to amorphize at an unusually low temperature of approximately 100 °C and multicomponent metal nanocatalysts additionally form on the amorphous surface as the temperature raises to 400 °C. Moreover, this investigation into the stability of the resulting amorphous layer under oxidizing conditions reveals that the amorphous structure can withstand a high-temperature oxidizing atmosphere (≥650 °C) only when it has undergone sufficient reduction for an extended period. Therefore, the coexistence of the active nanocatalysts and defective amorphous surface leads to a nearly 100% enhancement in the electrode resistance for the ORR over 200 h without significant degradation. These observations provide a new catalytic design strategy for using redox-dynamic perovskite oxide host materials.

Temperature-dependent Mn2+ emission in codoped CsPb2 (BrCl)5 perovskite nanocrystals

We prepared codoped CsPb2(BrCl)5 nanocrystal (NC) films by varying the Cu/Mn molar ratio using a facile two-step solution method. The Mn2+ emission peak is studied in the temperature range of 80–300 K. Strong electron–optical-phonon coupling causes an anomalous blueshift and linewidth broadening of the Mn2+ emission peak with increasing temperature. The average optical-phonon energy is approximately 50 meV. The activation energy reaches 79.32 meV, indicating that the introduction of Cu2+ in Mn-doped CsPb2(BrCl)5 NCs greatly enhances the energy transfer (ET) from the perovskite NC host to Mn2+, increasing the Mn2+ emission intensity. A clear understanding of the optical mechanism of Mn2+ emission is of great significance for the widespread application of codoped CsPb2(BrCl)5 NCs in optoelectronic devices.

Innovative approach to tailoring upconversion luminescence in Yb3+/Eu3+ doped CaZrO3 perovskite host matrix

This study presents the synthesis and characterization of upconverter nanostructures consisting of a perovskite host matrix, CaZrO3, co-doped with trivalent ytterbium (Yb3+) and europium (Eu3+), denoted as CaZrO3:Yb3+/Eu3+. Single-doped CaZrO3:Eu3+ samples were excited using a 394 nm UV source, while CaZrO3:Yb3+/Eu3+ samples were excited with a 980 nm diode laser source. Yb3+ ions efficiently absorb the 980 nm light and transfer the absorbed energy to the nearby ion Eu3+ ions, leading to the emission of visible light around 590, 614, and 655 nm, respectively. The emission spectra of Eu3+ ions exhibit an initial increase with increasing Yb3+ concentration, peaking at 7 mol%, followed by a decrease due to luminescence quenching. The decay lifetime of Eu3+ ions under 300 nm excitation decreases simultaneously with increasing Yb3+ concentration, indicating energy migration between Yb3+ and Eu3+. Detailed explanations of the energy transfer mechanism between Yb3+ and Eu3+ ions are provided, supported by equations and diagrams. This study provides valuable insights into the optimization of dopant concentrations for enhancing upconversion luminescence in CaZrO3:Yb3+/Eu3+ nanostructures, with 3 mol% Eu3+ concentration identified as optimal based on preliminary experiments. The findings presented in this paper contribute to the understanding of energy transfer processes in luminescence upconversion materials and highlight the potential of CaZrO3:Yb3+/Eu3+ nanostructures for applications in lighting, displays, and bio-imaging. This work represents a significant advancement in the field of upconversion luminescence emission, particularly in the utilization of CaZrO3 codoped with Yb3+ and Eu3+, and lays the foundation for further research in this area.

Confinement of methylammonium lead bromide nanocrystals in metal–organic frameworks as a stable scintillator for high-performance X-ray imaging

The development of perovskite nanocrystals (NCs) based composites with enhanced stability and exceptional photoelectric properties is of great significance for their application in scintillators for X-ray imaging, but it remains challenging. Herein, we demonstrate a novel and stable scintillator, achieved through a host–guest strategy involving the confinement of perovskite NCs, e.g., MAPbBr3 NCs, in metal–organic frameworks (MOFs). The host MOF, bio-MOF-100 (denoted as bMOF), facilitates the in-situ space-confined formation of MAPbBr3 NCs while providing quantum confinement, surface passivation, and protection to these guests. This host–guest strategy results in high exciton binding energy, bright and efficient luminescence, and significantly enhancing their stability against various factors such as air, heat, UV, solvents and X-ray irradiation. Consequently, this advancement prompts the transition of their application scenarios from the colloidal state to the solid state. The bMOF⊃MAPbBr3 scintillator exhibits a linear response to X-ray with a detection limit determined to be 170 nGyair s−1. Moreover, the bMOF⊃MAPbBr3–PMMA scintillator screen demonstrates high-quality X-ray imaging with an impressive spatial resolution of 14.7 lp mm−1. This work provides a new avenue for the development of perovskite NCs-based host–guest composites and paves the way for the broader implementation in solid-state optoelectronic applications.

Efficient and tunable white light emitting from Sb3+, Tb3+, and Sm3+ Co-doped Cs2NaInCl6 double perovskite via multiple energy transfer processes

Inorganic lead-free double perovskites have the advantages of low toxicity, broadband emission, and good stability, which make them promising luminescent materials for lighting applications. However, due to the limited regulation of their self-trapped exciton emission, it is still greatly challenging to achieve white light emitting from a single double perovskite host. Herein, efficient and tunable white light is realized in Cs2NaInCl6: Sb3+, Tb3+, Sm3+ double perovskite by controlling the ratios of the doped three ions with blue, green, and red emissions, respectively. The steady-state and transient fluorescence spectra of singly- and doubly-doped double perovskites reveal the existence of multiple energy transfer channels in the triply-doped phosphors, including from Sb3+ to Tb3+, Sb3+ to Sm3+, and Tb3+ to Sm3+. Benefiting from these channels, the color coordinates of the triply-doped phosphors can cross the whole white light area of the CIE chromaticity diagram by adjusting the ratios of the three dopants, and the maximum internal quantum yield of the white light phosphors is 66.61 %. The white emission phosphors show the characteristic of being independent of excitation wavelength within 310–360 nm. Furthermore, the emission intensity at 430 K of the white light phosphor Cs2NaInCl6: 0.01Sb3+, 0.65Tb3+, 0.20Sm3+ remains 50 % of that at room temperature. A WLED device fabricated with the phosphor and a 365 nm LED chip exhibits a high color rendering index of 90.9, correlated color temperature of 5469 K, and CIE coordinates of (0.333 and 0.328). The results indicate that the as-prepared double perovskite materials are promising candidates in the solid-state lighting field.

Halide exchange mediated cation exchange facilitates room temperature co-doping of d-and f-block elements in cesium lead halide perovskite nanoparticles.

This study presents a halide exchange mediated cation exchange reaction to co-dope d- and f-block elements in CsPbX3 NPs at room temperature. Addition of MnCl2 and YbCl3 to CsPbBr3 NPs induces ion exchange reactions generating the corresponding CsPbBr3/MnCl2YbCl3 NPs. In addition to the perovskite emission, the NPs display sensitized Mn2+ and Yb3+ emissions in concert spanning the UV, visible, and NIR spectral region. Structural and spectroscopic characterizations indicate a substitutional displacement of Pb2+ by the Mn2+ and Yb3+. The identity of the host halide in modulating the ion exchange reactions was also tested. An effective perovskite host NP is presented that can be used to incorporate d-f or f-f dopant combinations to realize a gamut of dopant emission lines. A charge trapping based photophysical model is developed that focuses on rational energy alignments to predict dopant emissions semi-empirically and aids the design of optimal perovskite host-multi-dopant combinations.

Development of Electrochemical Anion Doping Technique for Expansion of Functional Material Exploration

AbstractInstead of conventional cation doping strategy, anion doping is a promising new strategy for advances of energy conversion and storage technologies such as batteries, catalysts, electrolysis, and fuel cells. To synthesize mixed‐anion compounds, novel synthesis techniques such as topochemical reaction, high‐pressure reaction, solvothermal reaction have been developed. Despite these excellent synthesis techniques, synthesizable mixed‐anion compounds are still limited. For further expansion of the material exploration of mixed‐anion compounds, herein, an electrochemical anion doping technique is developed, which can flexibly control a species of anion, the doping rate and the degree of anion doping. The concept of the new synthesis technique is verified by F doping to the perovskite oxide La0.5Sr0.5CoO3−δ. Quantitative control of F in the perovskite host material is succeeded by using an electrochemical reactor composed of La0.5Sr0.5CoO3−δ‐BaF2|BaF2|PbF2‐Pb, and phase‐pure F‐doped La0.5Sr0.5CoO3−δ powder is obtained. Moreover, nano‐size crystalline domains with amorphous phase are formed on the particle surface under the high‐rate F doping, suggesting that tuning the anion doping rate enables the control of the formation of metastable phase. As demonstrated, the electrochemical anion doping technique opens up new possibilities for advances of energy materials by utilizing function of anionic species.

Study on structural and photoluminescence property of SrCeO3 and SrCe0.98Sm0.02O3 perovskites

Perovskites with improved structural and photoluminescence properties can be furnished by doping with rare earth elements. Strontium cerate perovskite host matrix plays a prime role in energy devices due to improved functional property, namely electrical conductivity. Electrochemical cells, hydrogen extractors, sensors have been greatly manufactured by innovators in past decade using doped strontium cerate perovskites. But only minimal innovation in the area of luminescence of this particular perovskite was found. In the present study, SrCeO3 and SrCe0.98Sm0.02O3 perovskites are synthesized for investigating the photoluminescence spectra. The perovskites are prepared by gel combustion technique. X-ray diffraction studies were carried out to investigate the evolution of the crystalline phase of the ceramic powder. Absorption bands in the UV region occur due to charge transfer transitions between the 4f orbital of Ce4+ and 2p orbital of oxygen ion in SrCeO3. Under UV excitations, the prepared perovskite nano phosphors show blue emission and orange-red emission respectively and was confirmed using CIE 1931 chromaticity diagram. The vibrational modes were further analysed using Raman spectra. So, these perovskites can be promising candidate as blue phosphor and red phosphor in light-emitting devices and applications.

Sub-Bandgap Sensitization of Perovskite Semiconductors via Colloidal Quantum Dots Incorporation.

By taking advantage of the outstanding intrinsic optoelectronic properties of perovskite-based photovoltaic materials, together with the strong near-infrared (NIR) absorption and electronic confinement in PbS quantum dots (QDs), sub-bandgap photocurrent generation is possible, opening the way for solar cell efficiencies surpassing the classical limits. The present study shows an effective methodology for the inclusion of high densities of colloidal PbS QDs in a MAPbI3 (methylammonium lead iodide) perovskite matrix as a means to enhance the spectral window of photon absorption of the perovskite host film and allow photocurrent production below its bandgap. The QDs were introduced in the perovskite matrix in different sizes and concentrations to study the formation of quantum-confined levels within the host bandgap and the potential formation of a delocalized intermediate mini-band (IB). Pronounced sub-bandgap (in NIR) absorption was optically confirmed with the introduction of QDs in the perovskite. The consequent photocurrent generation was demonstrated via photoconductivity measurements, which indicated IB establishment in the films. Despite verifying the reduced crystallinity of the MAPbI3 matrix with a higher concentration and size of the embedded QDs, the nanostructured films showed pronounced enhancement (above 10-fold) in NIR absorption and consequent photocurrent generation at photon energies below the perovskite bandgap.

Phase Stability of SrTi1-XFexO3- δ Under Solid Oxide Cell Fuel-Electrode Conditions: Implications for Related Exsolution Electrode Materials

Perovskite oxides with catalytically active metal nanoparticle exsolution are receiving considerable attention as alternative Solid Oxide Cell fuel-electrode materials. For exsolution, a small amount of a cation is substituted on the B-site of the base oxide and then is reduced out of the host lattice to form nanoparticles that promote electrochemical processes. During exsolution, the host lattice generally becomes more B-site deficient. In some cases, the oxide is made initially A-site deficient to compensate for the loss of B-site cations. Thus, the stability of these oxides under a range of stoichiometries and fuel electrode conditions is of interest.Here we focus on one perovskite host material of interest, SrTi1-xFexO3- δ (STF), which has shown good fuel electrode characteristics that can be enhanced by the substitution of Ru or Ni, resulting in exsolution to form Ru-Fe or Ni-Fe alloy nanoparticles, respectively. (1, 2) Although the amounts of Ru or Ni substituted are small, typically ~ 7% of the B-site cations, the co-exsolution of a comparable amount of Fe is usually observed, resulting in substantial B-site deficiency, potentially de-stabilizing the host perovskite phase. The stability of Fe in STF is also of interest because it helps to determine the Fe content of the alloy nanoparticles. (3)This study seeks to determine the stability of STF in various reducing fuel environments. While STF has been mostly studied as SrTi0.3Fe0.7O3-δ (STF-7), it is not known if this composition provides the best combination of stability and electrochemical performance. Thus, a few additional compositions, SrTi0.5Fe0.5O3- δ (STF-5), SrTi0.4Fe0.6O3- δ (STF-6), and SrTi0.2Fe0.8O3- δ (STF-8), have been studied. In general, the Fe-rich compositions are expected to possess higher electronic and ionic conductivity, leading to good electrochemical performance, whereas the more Ti-rich compositions are expected to provide better stability. Exposure to 97% H2 – 3% H2O at 850°C for 4 h resulted in STF decomposition into BCC α-Fe and a Ruddlesden-Popper (RP) phase, but the decomposition became more limited for the more Ti-rich compositions (Figure 1a). The main Fe peak overlaps with one of the RP peaks, but the presence of α-Fe particles is clearly visible in STEM energy dispersive x-ray spectroscopy chemical mapping, shown for STF-7 in Figure 1b. Figure 1c shows that there is a critical p(O2), 1.3 x 10-20 atm, below which decomposition of perovskite STF-7 occurs. In addition to ex situ XRD as shown in Figure 1, in situ XRD results will be presented and used to confirm and quantify phase changes in combination with thermogravimetric analysis (TGA). Additionally, the conductivity and electrochemical performance of the various STF compositions will be reported and discussed relative to the phase change from perovskite to Ruddlesden Popper and the Fe exsolution. The other main materials variable to be explored is the A-to-B site stoichiometry, which will be studied over the range expected during exsolution. The implications of these results for various exsolution electrode compositions will be discussed.Figure 1: a) Reductions of STF-5 through STF-8 all yield significant decomposition as the initially pristine perovskite acquires several additional peaks. b) Using energy dispersive x-ray spectroscopy, it can be shown that significant Fe deposits appear in STF-7 after reduction at 850°C (effective pO2 1.2e-21 atm for 4 hours). c By increasing pO2 by a factor of 10, XRD patterns for STF-7 show no clear Ruddlesden-Popper or α-Fe peaks, indicating that decomposition requires significantly reducing conditions and that STF may remain stable under more oxidizing conditions.References R. Glaser, T. Zhu, H. Troiani, A. Caneiro, L. Mogni and S. Barnett, Journal of Materials Chemistry A, 6, 5193 (2018).T. Zhu, H. Troiani, L. V. Mogni, M. Santaya, M. Han and S. A. Barnett, Journal of Power Sources, 439 (2019).T. Zhu, H. E. Troiani, L. V. Mogni, M. Han and S. A. Barnett, Joule, 2, 478 (2018). Figure 1

The development of a new efficient red phosphor based on Eu2+ doped traditional inorganic oxygenate-perovskite compounds

The halide-perovskite type phosphors have been aroused extensive attention in recent years for their high quantum efficiency, but traditional oxygenate-perovskite type phosphors with Eu2+ activator have not been studied extensively so far. To fill this void, we dope Eu2+ into a typical perovskite host lattice SrZrO3 to produce an efficient phosphor SrZrO3:xEu2+. Theoretical calculation reveals that SrZrO3 has an indirect band gap of 3.776 eV. Phosphors SrZrO3:xEu2+ show bright red emission peaking at 605 nm under 450 nm blue light excitation with the full width at half maximum (FWHM) of 60 nm. The optimized concentration of Eu2+ is x = 0.10, and the quenching mechanism originates from the dipole-dipole interactions. The external quantum yield of optimal sample, SrZrO3:0.10Eu2+ can reach up to a high value of 50%. Temperature dependent luminescent properties studies show that the fluorescence integrated intensity of the sample at 425 K remains at 80% of that at 300 K. Finally, a white light-emitting diode (LED) is fabricated with color rendering index of 73 and color temperature of 3576 K. Thus, phosphor SrZrO3:0.10Eu2+ has great potential in fields of WLED lamp.

Broad Dual Emission by Codoping Cr3+ (d→d) and Bi3+ (s→p) in Cs2Ag0.6Na0.4InCl6 Double Perovskite

AbstractA phosphor emitting both white light and broad near‐infrared (NIR) radiation can simultaneously provide visual inspection and early signs of rotting of food products. The broad NIR emission is absorbed by the vibrational overtones of water molecules present in food items, providing the non‐invasive image contrast to assess the food freshness. Here we design a phosphor, namely, Cr3+‐Bi3+‐codoped Cs2Ag0.6Na0.4InCl6, that simultaneously emit warm white light and broad NIR (1000 nm) radiation with quantum yield 27 %. This dual emitter is designed by combining the features of s2‐electron (Bi3+) and d3‐electron (Cr3+) doping in a weak crystal field of the halide perovskite host. excitation of Bi3+, using a commercial 370 nm ultraviolet light‐emitting‐diodes (UV‐LED), yields both the emissions. A fraction of the excited Bi3+ dopants emit the warm white light, and the other fraction transfers its energy non‐radiatively to Cr3+. Then the Cr3+ de‐excites emitting broad NIR emission. Temperature dependent (6.4–300 K) photoluminescence in combination with Tanabe‐Sugano diagram show that the Cr3+ experiences a weak crystal field ( =2.2), yielding the NIR emission. As a proof of concept, we fabricated a panel containing 122 phosphor‐converted LEDs, demonstrating its capability to inspect food products.

Broad Dual Emission by Codoping Cr3+ (d→d) and Bi3+ (s→p) in Cs2 Ag0.6 Na0.4 InCl6 Double Perovskite.

A phosphor emitting both white light and broad near-infrared (NIR) radiation can simultaneously provide visual inspection and early signs of rotting of food products. The broad NIR emission is absorbed by the vibrational overtones of water molecules present in food items, providing the non-invasive image contrast to assess the food freshness. Here we design a phosphor, namely, Cr3+ -Bi3+ -codoped Cs2 Ag0.6 Na0.4 InCl6 , that simultaneously emit warm white light and broad NIR (1000 nm) radiation with quantum yield 27 %. This dual emitter is designed by combining the features of s2 -electron (Bi3+ ) and d3 -electron (Cr3+ ) doping in a weak crystal field of the halide perovskite host. excitation of Bi3+ , using a commercial 370 nm ultraviolet light-emitting-diodes (UV-LED), yields both the emissions. A fraction of the excited Bi3+ dopants emit the warm white light, and the other fraction transfers its energy non-radiatively to Cr3+ . Then the Cr3+ de-excites emitting broad NIR emission. Temperature dependent (6.4-300 K) photoluminescence in combination with Tanabe-Sugano diagram show that the Cr3+ experiences a weak crystal field ( =2.2), yielding the NIR emission. As a proof of concept, we fabricated a panel containing 122 phosphor-converted LEDs, demonstrating its capability to inspect food products.

Enhanced redox performance of LaFeO3 perovskite through in-situ exsolution of iridium nanoparticles for chemical looping steam methane reforming

Chemical looping steam methane reforming (CL-SMR) can produce high-purity hydrogen without additional separation units. However, the low reactivity of LaFeO3 oxygen carrier towards methane restricts the overall process performance. To enhance the redox activity of widely used LaFeO3 perovskite, a small amount of iridium was introduced to LaFeO3. The presence of iridium significantly enhanced both particle reduction and oxidation, and the particle preparation pathways of oxygen carriers greatly affected the long-term performance. The overall enhancement from the incorporation of iridium was demonstrated by density functional theory calculations. Despite these beneficial effects of iridium addition, surface iridium species prepared by an impregnation method were severely aggregated during successive redox cycling, leading to deactivation of the particles. In contrast, B-site incorporation of iridium leads to the exsolution of IrOx nanoparticles anchored on the perovskite host as well as to enhanced redox stability, which is essential for the long-term operation of the chemical looping process.

A generic lanthanum doping strategy enabling efficient lead halide perovskite luminescence for backlights

Metal halide perovskites films have attracted great interest because of their solution-proceed fabrication and potential applications for next-generation displays. However, their non-ideal photoluminescence quantum efficiency (PLQE) and stability still does not meet the requirements of displays. Here, we adopt lanthanum ion (La3+) doping strategy to enhance its luminescence performance and the possibility of taking it to commercialization. In addition to the entry of lanthanum ions into the lattice to greatly improve the crystal quality, the excess La3+ gives rise to the formation of newly developed formamidinium cesium lanthanum bromine, (FA, Cs)2LaBr5, which provides additional energy transport pathways, therefore concentrating more energy onto the perovskite host. Consequently, a near-unity PLQE of 99.5% is realized in standardized green-emission cesium (Cs)/formamidinium (FA) mixed FA0.7Cs0.3PbBr3 perovskite films. The introduction of La3+ can also lead to markedly stability with nearly 1000 days’ shelf storage half-lifetime and 400 hours’ light-irradiation T90 lifetime as well as much-enhanced color purity. Moreover, the films with La3+ doping enable full-visible spectral enhancement and high-performance white light emission and trichromatic luminescence with 98.9% coverage of the color gamut area required for the Rec. 2020 standard, which suggest that perovskite films have great application potential for backlights in liquid crystal display technologies.

Real-time insight into the multistage mechanism of nanoparticle exsolution from a perovskite host surface

In exsolution, nanoparticles form by emerging from oxide hosts by application of redox driving forces, leading to transformative advances in stability, activity, and efficiency over deposition techniques, and resulting in a wide range of new opportunities for catalytic, energy and net-zero-related technologies. However, the mechanism of exsolved nanoparticle nucleation and perovskite structural evolution, has, to date, remained unclear. Herein, we shed light on this elusive process by following in real time Ir nanoparticle emergence from a SrTiO3 host oxide lattice, using in situ high-resolution electron microscopy in combination with computational simulations and machine learning analytics. We show that nucleation occurs via atom clustering, in tandem with host evolution, revealing the participation of surface defects and host lattice restructuring in trapping Ir atoms to initiate nanoparticle formation and growth. These insights provide a theoretical platform and practical recommendations to further the development of highly functional and broadly applicable exsolvable materials.

Highly efficient visible and near-infrared luminescence of Sb3+, Tm3+ co-doped Cs2NaYCl6 lead-free double perovskite and light emitting diodes

Near-infrared (NIR) luminescent materials have been widely used in biomedicine, optical communication and other fields due to their unique photophysical properties. However, the development of efficient NIR luminescent materials is still a challenge. Herein, Sb3+, Tm3+ co-doped Cs2NaYCl6 double perovskite single crystals (SCs) have been synthesized. Benefiting from the crystal structure and rare earth lattice of rare earth-based double perovskite host, lanthanide ions can be doped effectively, and the optimal NIR photoluminescence quantum yield (PLQY) of Cs2NaYCl6:Sb3+, Tm3+ SCs is up to 20.2%. The energy transfer mechanism was systematically surveyed by steady-state spectroscopy. Furthermore, a compact visible and NIR light emitting diode was fabricated by coating Cs2NaYCl6:Sb3+, Tm3+ SCs on a commercial 320 nm LED chip. This light source has a promising application prospect in multifunctional lighting.

Development of the Composite Thermoluminescent Detectors Based on the Single Crystalline Films and Crystals of Perovskite Compounds.

This work is dedicated to the development of new types of composite thermoluminescent detectors based on the single crystalline films of Ce-doped GdAlO3 perovskite and Mn-doped YAlO3 and (Lu0.8Y0.2)AlO3:Mn perovskites as well as Ce and Pr-doped YAlO3 single crystal substrates. These detectors were obtained using the Liquid Phase Epitaxy growth method from the melt solution based on the PbO-B2O3 fluxes. Such composite detectors can by applied for the simultaneous registration of different components of mixed ionization fluxes using the differences between the thermoluminescent glow curves, recorded from the film and crystal parts of epitaxial structures. For creation of the new composite detectors, we considered using, for the film and crystal components of epitaxial structures (i) the different perovskite matrixes doped with the same type of activator or (ii) the same perovskite host with various types of activators. The thermoluminescent properties of the different types of epitaxial structures based on the abovementioned films and crystal substrates were examined in the conditions of β-particles and X-ray excitation with aim of determination of the optimal combination of perovskites for composite detectors. It was shown that, among the structures with all the studied compositions, the best properties for the simultaneous thermoluminescent detection of α- and X-rays were the GdAlO3:Ce film/YAlO3:Ce crystal epitaxial structure.

Band-Gap Engineering of Layered Perovskites by Cu Spacer Insertion as Photocatalysts for Depollution Reaction

A multi-step ion-exchange methodology was developed for the fabrication of Cu(LaTa2O7)2 lamellar architectures capable of wastewater depollution. The (001) diffraction line of RbLaTa2O7 depended on the guest species hosted by the starting material. SEM and TEM images confirmed the well-preserved lamellar structure for all intercalated layered perovskites. The UV–Vis, XPS, and photocurrent spectroscopies proved that Cu intercalation induces a red-shift band gap compared to the perovskite host. Moreover, the UV–Vis spectroscopy elucidated the copper ions environment in the Cu-modified layered perovskites. H2-TPR results confirmed that Cu species located on the surface are reduced at a lower temperature while those from the interlayer occur at higher temperature ranges. The photocatalytic degradation of phenol under simulated solar irradiation was used as a model reaction to assess the performances of the studied catalysts. Increased photocatalytic activity was observed for Cu-modified layered perovskites compared to RbLaTa2O7 pristine. This behavior resulted from the efficient separation of photogenerated charge carriers and light absorption induced by copper spacer insertion.

Anomalous low-energy carrier dynamics of stripe-type charge ordered Pr0.5Sr0.5MnO3 thin film revealed by magneto-terahertz spectroscopy

The perovskite manganites host a range of charge- and orbital-ordered phases wherein the intrinsic and extrinsic controls of magnetic field, doping, epitaxial strain, chemical pressure, etc., induce subtleties of phase transition. The Pr0.5Sr0.5MnO3 (PSMO) is one such system that possesses a unique stripe-type charge-order manifesting in anisotropic transport. It exhibits a Drude-type and charge-density-wave (CDW) type of low-energy phases; the magnetic field is contemplated as a key control for both these phases; however, it has not yet been explored. Here, we have investigated the magnetic-field dependence of Drude-type terahertz (THz) carriers dynamics and the CDW type of low-energy excitations along two non-identical orthogonal in-plane axes of the (110) epitaxial thin film in the energy range of 1–7 meV using magneto-THz time-domain spectroscopy in Faraday geometry. While THz Drude conductivity expectedly increases with the increasing magnetic field, the CDW type of resonance absorption peak anomalously strengthens with the field. The origin of this unusual field-induced stabilization of the CDW-type mode is expected to lie in the d(x2–y2) orbital ordering in the A-type antiferromagnetic ordered state and anisotropic charge ordering. This study brings out a unique facet of the effect of magnetic field on orbital ordering of anisotropic stripe-type charge-ordered PSMO, which has potential THz modulation and switching applications.