Search

Luminescence intensity ratio (LIR) based optical thermometers have attracted lots of attention. In case of color tunable luminescence with the variation of LIR, "RGB colorimetry" based on convenient temperature sensing using a smartphone or digital camera is available. However, narrow emission bands with primary colors are needed for avoiding color crosstalk and achieving high sensitivities. In this paper, Mn4+ and Mn2+ coactivated CaAl12O19 (CAO) phosphors are reported that show a narrow red emission of Mn4+ and green one of Mn2+ with the number of the two ions controlled by lanthanide ions through manipulation of self‐reduction of Mn4+ to Mn2+ in air. The self‐reduction in CAO via the addition of Ce4+ is mainly studied. First‐principles calculation shows that the self‐reduction is driven by Ca vacancies that are produced in aliovalent substitution of Ce4+ for Ca2+ and can reduce the formation energy of Mn2+. The comparative study of temperature sensing based on LIR and RG colorimetry is conducted. The relative sensitivity based on LIR is high as 4.5% K−1 at 373 K and that for RG colorimetry can reach 2% K−1 at 350 K. These findings provide a strategy for manipulation of manganese valance states and a phosphor for RG colorimetry temperature sensing. [ABSTRACT FROM AUTHOR]

Imine‐based covalent organic frameworks (COFs) are promising for photocatalytic water splitting, but their performance is often constrained by inefficient charge separation due to the high electron localization nature of polar imine bonds. In this study, we have optimized the electron delocalization across the imine linkage within a COF by implementing a charge compensation effect. This effect is achieved when a strong electron‐donating thieno[3,2‐b]thiophene linker is directly attached to the iminic carbon of a zinc‐porphyrinic COF. This modification significantly reduces the electron binding effect within the imine bonds of the COF, facilitating both in‐plane charge separation and out‐plane charge transfer to the catalytic site. Conversely, the use of strong electron‐withdrawing pyrizine linker aggravates the electron localization at the imine linkage in the ZnP−Pz variant. Consequently, ZnP−Tt shows a substantially improved photocatalytic water‐splitting activity under visible light irradiation, with a hydrogen evolution of 44288±2280 μmol g−1 in 4 h, which exceeds the ZnP−Pz counterpart by a factor of 10. These results offer fresh perspectives for the design of imine‐based COFs to overcome their limitations in charge separation efficiency. [ABSTRACT FROM AUTHOR]

Oxygen vacancy is the most common type of point defects in functional oxides, and it is known to have profound influence on their properties. This is particularly true for ferroelectric oxides since their interaction with ferroelectric polarization often dictates the ferroelectric responses. Here, we study the influence of the concentration of oxygen vacancies on the stability of ferroelectric domain walls (DWs) in BiFeO3, a material with a relatively narrow bandgap among all perovskite oxides, which enables strong interactions among electronic charge carriers, oxygen vacancies, and ferroelectric domains. It is found that the electronic charge carriers in the absence of oxygen vacancies have essentially no influence on the spatial polarization distribution of the DWs due to their low concentrations. Upon increasing the concentration of oxygen vacancies, charge‐neutral DWs with an originally symmetric polarization distribution symmetric around the center of the wall can develop a strong asymmetry of the polarization field, which is mediated by the electrostatic interaction between polarization and electrons from the ionization of oxygen vacancies. Strongly charged head‐to‐head DWs that are unstable without oxygen vacancies can be energetically stabilized in the off‐stoichiometric BiFeO3−δ with δ ∼ 0.02 where ionization of oxygen vacancies provides sufficient free electrons to compensate the bound charge at the wall. Our results delineate the electrostatic coupling of the ionic defects and the associated free electronic charge carriers with the bound charge in the vicinity of neutral and charged DWs in perovskite ferroelectrics. [ABSTRACT FROM AUTHOR]

Oxygen vacancy is the most common type of point defects in functional oxides, and it is known to have profound influence on their properties. This is particularly true for ferroelectric oxides since their interaction with ferroelectric polarization often dictates the ferroelectric responses. Here, we study the influence of the concentration of oxygen vacancies on the stability of ferroelectric domain walls (DWs) in BiFeO3, a material with a relatively narrow bandgap among all perovskite oxides, which enables strong interactions among electronic charge carriers, oxygen vacancies, and ferroelectric domains. It is found that the electronic charge carriers in the absence of oxygen vacancies have essentially no influence on the spatial polarization distribution of the DWs due to their low concentrations. Upon increasing the concentration of oxygen vacancies, charge‐neutral DWs with an originally symmetric polarization distribution symmetric around the center of the wall can develop a strong asymmetry of the polarization field, which is mediated by the electrostatic interaction between polarization and electrons from the ionization of oxygen vacancies. Strongly charged head‐to‐head DWs that are unstable without oxygen vacancies can be energetically stabilized in the off‐stoichiometric BiFeO3−δ with δ ∼ 0.02 where ionization of oxygen vacancies provides sufficient free electrons to compensate the bound charge at the wall. Our results delineate the electrostatic coupling of the ionic defects and the associated free electronic charge carriers with the bound charge in the vicinity of neutral and charged DWs in perovskite ferroelectrics. [ABSTRACT FROM AUTHOR]

Near‐infrared‐II (NIR‐II) phosphors are extensively used as NIR phosphor‐converted light‐emitting diodes across various applications. Nonetheless, their application in fiber communication remains underexplored. Furthermore, efficiency challenges persist in developing broadband NIR crystal fiber amplifiers. A series of the Y3−yAl5−xO12:xCr,yCa2+ phosphors with boosted Cr4+ concentration via calcium charge compensation is synthesized, and the optimized sample is fabricated to crystal fibers to reveal the application of the NIR‐II phosphors to fiber communication. The fabricated Cr4+‐doped crystal fiber, exhibiting broadband Cr4+ emission within 1100–1600 nm, effectively covers the high‐transmission loss region caused by water absorption in the telecommunication band. Comprehensive characterization and analyses of the Cr4+ are discussed. Y2.84Al4.9O12:0.1Cr,0.16Ca2+ crystal fiber, fabricated through phosphor synthesis, pellets' production, and the laser‐heated pedestal growth method, exhibits superior photoluminescence compared to the commercial Cr4+‐doped Y3Al5O12 crystal fiber. Here the potential of NIR‐II phosphors is highlighted in enhancing fiber communication and valuable insights for their future application are provided. [ABSTRACT FROM AUTHOR]

Mn4+ activated fluoride red phosphors are used in warm white light emitting diodes (WLEDs). However, their inherently low moisture resistance is a major barrier to their use in high humidity conditions. In this work, the Nb-based oxyfluoride phosphors A x NbOF y :Mn4+ (A = Na, Cs; x = 2, 3; y = 5, 6) were synthesized by the co-precipitation method. The crystal structure, morphology, and luminescence properties are investigated with composition variation. The non-equivalent replacement of Nd5+ ions by Mn4+ results in bright red emission under blue light excitation. These phosphors showed very good moisture resistant luminescence. The best performance was achieved by the Na 3 NbOF 6 :0.1%Mn4+, which retained 98 % of the initial fluorescence intensity after immersion in water for 60 min. In addition, the W6+ and Mo6+ are used to compensate for the charge difference between Mn4+ and Nd5+ in Na 3 NbOF 6 :Mn4+. The compensated phosphors have shown large enhancements of 169 % (W6+) and 168 % (Mo6+) in luminescence intensity. This strategy of non-equivalent doping approach of Mn4+ into the Nb-based oxyfluoride materials and the charge compensation by W6+/Mo6+ to enhance the luminescence intensity provides a new way to realize high performance red phosphors for WLEDs. [ABSTRACT FROM AUTHOR]

La-doped BaTiO 3 ceramics are essential materials in electronic devices, finding applications in multilayer ceramic capacitors and positive temperature coefficient thermistors. While the electrical properties of La-doped BaTiO 3 have been investigated, the impact of its room-temperature resistivity anomaly on dielectric properties remains unclear. We synthesized pristine and La-doped BaTiO 3 (0.1 – 0.5 mol%) powders via hydrothermal methods, and then sintered bulk samples. Their resistivities (DC and AC), Curie temperature, room-temperature dielectric constant, and lattice volume with varying La doping concentrations were characterized. Beyond 0.3 mol%, the shift from electronic to ionic charge compensation mechanisms resulted in abrupt changes in resistivities, Curie temperature, and dielectric constant near 0.3 mol%. Given minimal changes in average grain size and relative density near 0.3 mol% La, the dominant factor influencing the dielectric constant peaking near this concentration was the shift in charge compensation mechanism. [ABSTRACT FROM AUTHOR]

Highly efficient blue-cyan phosphors can fill the cyan gap in conventional white light-emitting diode (LED) devices to improve the spectral continuity while effectively increasing the white LED colour rendering index (Ra). In this study, Ba 0·94 Al 2- x Ga x Si 2 O 8 :0.06Ce3+, M+ (Li, Na, K, x = 0–0.8) blue-cyan phosphors with a feldspar structure were prepared by a high-temperature solid-phase method using charge compensation and cation substitution strategies. The barium (Ba) vacancy due to the charge-imbalance substitution of Ce3+ is compensated by the different charge compensators Li+, Na+, and K+. The charge compensators affect the luminescence performance of the samples, with the K+-compensated samples showing the greatest enhancement, with intensities up to 1.8 times that of the uncompensated samples. The cation substitution strategy using Ga3+ to partially replace Al3+ further improves the luminescence performance of the Ba 0·94 Al 2 Si 2 O 8 :0.06Ce3+, 0.04 K+ sample, and the excitation band is also improved. In this case, the luminescence intensity of the Ba 0·94 Al 2 Si 2 O 8 :0.06Ce3+ luminescent material is increased by a factor of 6, and a broadband blue-cyan phosphor with a full-width at half-maximum of 118 nm containing blue, cyan and green is obtained. The co-doping of charge compensators and partial cation substitution improved the luminescence performance of phosphors. The representative sample Ba 0·94 Al 1.6 Ga 0.4 Si 2 O 8 :0.06Ce3+, 0.04 K+ has a luminescence intensity at a temperature of 150 °C that is 83.2% of that at room temperature and good thermal stability. The combination of 365 nm near-ultraviolet (NUV) LED chips with Ba 0·94 Al 1.6 Ga 0.4 Si 2 O 8 :0.06Ce3+, 0.04 K+ and the commercial red powder (Ca, Sr)AlSiN 3 :Eu2+ yields a white LED device with an Ra of up to 93 and a correlated colour temperature (CCT) of 4825 K. These results show that the blue-cyan phosphor complements the cyan component while simplifying the manufacturing process of white LEDs. [ABSTRACT FROM AUTHOR]

In this study, we investigated the phase transitions and thermoelectric properties of charge-compensated hakite (ZnxCu12−xSb4Se13) as a function of Zn content. Based on X-ray diffraction and a differential scanning calorimetric phase analysis, secondary phases (permingeatite and bytizite) transformed into hakite depending on the Zn content, while Zn2Cu10Sb4Se13 existed solely as hakite. Nondegenerate semiconductor behavior was observed, exhibiting increasing electrical conductivity with a rising temperature. With an increase in Zn content, the presence of mixed phases of hakite and permingeatite led to enhanced electrical conductivity. However, Zn2Cu10Sb4Se13 with a single hakite phase exhibited the lowest electrical conductivity. The Seebeck coefficient exhibited positive values, indicating that even after charge compensation (electron supply) by Zn, p-type semiconductor characteristics were maintained. With the occurrence of an intrinsic transition within the measured temperature range, the Seebeck coefficient decreased as the temperature increased; at a certain temperature, Zn2Cu10Sb4Se13 exhibited the highest value. Thermal conductivity showed a low temperature dependence, obtaining low values below 0.65 Wm−1K−1. A power factor of 0.22 mWm−1K−2 and dimensionless figure of merit of 0.31 were achieved at 623 K for ZnCu11Sb4Se13. [ABSTRACT FROM AUTHOR]

Luminescent materials with emissions at specific wavelengths, which have a relatively lower proportion of emissions in the solar spectrum, have great prospects for use in production and daily life. In this study, SrGaB2O7 deep‐blue phosphors doped with Bi3+ are synthesized, it has 430 nm deep‐blue emissions and a low proportion of emissions relative to 470–660 nm visible light in the solar spectrum. By co‐doping with alkali metal ions to compensate for the charge, the emission intensities and absolute quantum yields of the phosphors can be effectively improved. The SrGaB2O7:0.01Bi3+, 0.01K+ deep‐blue phosphor has a high quantum yield of 85% and negative thermal quenching properties. Moreover, the SrGaB2O7:0.01Bi3+, 0.01K+ deep‐blue phosphor can be packaged with different potting adhesives to form light‐emitting diodes (LEDs), exhibiting excellent luminescent performances and promising application prospects. [ABSTRACT FROM AUTHOR]

In this study, we thoroughly investigate the structural and luminescent features of ZnO nanoparticles doped with Eu3+ and co-doped with Dy3+, exploring the impact of Li+ and K+ incorporation during the precipitation process. The synthesized nanoparticles were comprehensively characterized using X-ray diffraction (XRD), Fourier transmission infrared (FTIR), Energy dispersive spectroscopy (EDS), and photoluminescence (PL) techniques. The XRD analysis conclusively verified the presence of the hexagonal wurtzite phase in the ZnO nanoparticles. PL assessment of undoped ZnO revealed a well-defined and narrow exciton band peaked at 390 nm, accompanied by a broad defect-related band spanning from 450 nm to 750 nm. For ZnO:Eu3+ phosphors, distinct emission peaks emerged at 590 nm, 618 nm, and 696 nm when excited at 349 nm, corresponding to the 4 f electron transition inherent to Eu3+ ions. The optimized doping level for the ZnO:xEu3+ sample was determined to be 7 wt%. The mechanism of concentration quenching was identified as dipole-quadrupole interaction. Co-doping with Li+ as a charge compensator resulted in a threefold enhancement in the luminescence intensity of the red-emitting ZnO:Eu3+, Li+. As the temperature decreases, the luminescence intensity of Eu3+ transitions in ZnO:7 wt% Eu3+ diminishes due to less efficient energy transfer among Eu3+ ions, while the intrinsic broad band from ZnO fades away, emphasizing the temperature-sensitive nature of the material. The addition of Dy3+ as a co-dopant to ZnO:Eu3+ induces a counterintuitive effect, where an increase in Dy3+ concentration unexpectedly results in a decrease in Eu3+ emission peak intensity. This unconventional behavior highlights a complex interplay between Dy3+ and Eu3+ ions, suggesting the influence of spatial factors, competing processes, and potential dopant aggregation within the ZnO lattice. The CIE analysis conducted on ZnO:Eu3+, Dy3+, and Li+ nanoparticles demonstrated precise control over the emitted light, enabling the fine-tuning of their optical properties for applications in displays. [ABSTRACT FROM AUTHOR]

This study compares HfO2 ceramics synthesized using sol–gel and combustion methods, emphasizing the impact of the method of synthesis on the resulting properties of the material. The research findings illustrate morphological differences between sol–gel and combustion-derived HfO2. While sol–gel samples displayed irregular nanoparticles with pronounced boundaries, combustion samples revealed more homogeneous structures with particles tending towards coalescence. It was discerned that Eu3+ doping induced oxygen vacancies, stabilizing the tetragonal phase, while subsequent doping with Nb5+ significantly reduced these vacancies, which was also observed in photoluminescence analysis. Furthermore, combustion synthesis left fewer organic residues, with urea presence during synthesis contributing to residual organic components in the material. XPS analysis was used to evaluate the presence of oxygen-deficient hafnia sub-oxide in the samples. The study underscores the important role of tailored synthesis methods in optimizing the properties and applications of HfO2.

Cathode materials have been playing an important role in the development of high-energy, safe and low-cost lithium-ion batteries. However, the widely used single-phase cathode materials are facing great challenges in solving the mileage and safety problems related to electric vehicles due to their inherent structural defects. Intergrown design of bulk structure is believed to be one of the most fundamental ways to improve structural stability and capacity for cathode materials. Due to the diversity of structural configurations, the systematic understanding is still lack for the intergrown structures of different combinations. Therefore, it is very desirable, but also of great importance to summarize the current progress and challenges for intergrown cathodes. In this review, we comprehensively reviewed the design and synthesis methods of intergrown cathodes including layered-spinel intergrown structures, layered-rocksalt intergrown structures, and spinel-rocksalt intergrown structured cathode materials. The charge compensation mechanism of intergrown cathodes with different structural configurations was analyzed in depth, and a targeted optimization schematic diagram was also proposed. Finally, combined with advanced characterization techniques, the understanding of the structural changes has been deepened for the intergrown cathodes during the electrochemical process. It is hoped this review should shed light on the development of advanced cathode materials for the next-generation Li-ion batteries.

Defect engineering is an effective and fascinating strategy for improving thermostability of phosphor. However, there is the challenge for the diminishment of luminescence intensity, originating from the defect as quenching center. In this work, the defect is introduced through the non-equivalent substitution of Sm3+ for Ca2+, resulting in zero-thermal-quenching (zero-TQ) behavior in Ca 9 ZnK(PO 4) 7 :0.07Sm3+ (CZKP:0.07Sm3+). Meanwhile, the incorporation of charge compensators (Li+ and Na+) reduces quenching centers and enhances the luminescent performance of the typical CZKP:0.07Sm3+ phosphor, maintaining zero-TQ behavior. Finally, the resulting phosphor are applied to assemble white/red light-emitting diodes (LED) devices, demonstrating highly stable chromatic performance and promising in white/plant growth lighting. This work provides a reference for the effective defect utilization in constructing highly thermostable phosphor. [ABSTRACT FROM AUTHOR]

A series of K2Ca1-xP2O7:xEu3+ phosphors were prepared by a high-temperature solid-state reaction method. The crystal structure was analyzed by X-ray diffraction (XRD). Fluorescence spectra, decay curves, and color coordinates were investigated. Under excitation at 393 nm, the strongest emission peak was located at 590 nm, corresponding to the 5D0→7F1 transition of Eu3+, and the sub-strongest one was located at 612 nm which belongs to the 5D0→7F2 transition of Eu3+. XRD results show that the patterns doped with a small amount of Eu3+ were fitted well with the standard card of K2CaP2O7, while the pattern with the doping of high concentration Eu3+ (heavy-doping) indicated the co-existence of K2CaP2O7 and EuPO4 phase which leads to luminescent intensity of phosphors enhance remarkablely. The concentration quenching mechanism was explained through dipole-dipole interaction. Different doping amounts of Eu3+ and charge compensators will affect the symmetry of the host lattice, thereby affecting the emission intensity ratio of orange and red light. The color coordinates of K2Ca0.49P2O7:0.51Eu3+ and K2Ca0.33P2O7:0.67Eu3+, 0.1Na+ phosphor were near the red region, which was close to commercial red-emitting phosphors Y2O3:Eu3+ and standard red light, respectively. A series of K2CaP2O7 phosphors emitting orange-red light with different concentrations of Eu3+ doping and alkali metal ions co-doping were synthesized via a high-temperature solid-state method, and their structure and luminescent properties were characterized. A new strategy for adjusting the light color parameters of K2CaP2O7 phosphors has been constructed. [ABSTRACT FROM AUTHOR]

This study compares HfO2 ceramics synthesized using sol–gel and combustion methods, emphasizing the impact of the method of synthesis on the resulting properties of the material. The research findings illustrate morphological differences between sol–gel and combustion-derived HfO2. While sol–gel samples displayed irregular nanoparticles with pronounced boundaries, combustion samples revealed more homogeneous structures with particles tending towards coalescence. It was discerned that Eu3+ doping induced oxygen vacancies, stabilizing the tetragonal phase, while subsequent doping with Nb5+ significantly reduced these vacancies, which was also observed in photoluminescence analysis. Furthermore, combustion synthesis left fewer organic residues, with urea presence during synthesis contributing to residual organic components in the material. XPS analysis was used to evaluate the presence of oxygen-deficient hafnia sub-oxide in the samples. The study underscores the important role of tailored synthesis methods in optimizing the properties and applications of HfO2. [ABSTRACT FROM AUTHOR]

Mn4+‐activated CaAl12O19 (CAO: Mn4+) is recognized as a promising candidate for red phosphor used in wide color gamut displays. However, the spontaneous self‐reduction of Mn4+ to Mn2+ occurs for charge compensation through Mn2+‐Mn4+ substitution for Al3+‐Al3+, lowering the quantum efficiency of Mn4+. To suppress the self‐reduction, some divalent metal ions, including Ba2+, Sr2+, Cd2+, Zn2+, and Mg2+, are added for charge compensation instead of Mn2+, but only small luminescence enhancement is observed. In this paper, remarkable luminescence enhancement in CAO: Mn4+ via co‐doping Be2+ is reported. The photoluminescence properties are studied as a function of Be2+ doping concentration, and the optimal Be2+ concentration of 0.01 is found. The internal quantum efficiency of 74.9% and external quantum efficiency of 56.3% are achieved under UV excitation, higher than those via co‐doping other divalent metal ions. This study indicates that the addition of Be2+ dominates the charge compensation because Be2+ is closer to Al3+ in size than Mn2+ and other divalent metal ions. The backlight light‐emitting diodes using CAO: Mn4+, Be2+ are fabricated, exhibiting a 110.1% Nation Television Standards Committee (NTSC) color gamut, wider than both the current commercial backlight using K2SiF6: Mn4+ (KSF) red phosphor and the conventional one using YAG yellow phosphor. [ABSTRACT FROM AUTHOR]

Mn4+‐activated CaAl12O19 (CAO: Mn4+) is recognized as a promising candidate for red phosphor used in wide color gamut displays. However, the spontaneous self‐reduction of Mn4+ to Mn2+ occurs for charge compensation through Mn2+‐Mn4+ substitution for Al3+‐Al3+, lowering the quantum efficiency of Mn4+. To suppress the self‐reduction, some divalent metal ions, including Ba2+, Sr2+, Cd2+, Zn2+, and Mg2+, are added for charge compensation instead of Mn2+, but only small luminescence enhancement is observed. In this paper, remarkable luminescence enhancement in CAO: Mn4+ via co‐doping Be2+ is reported. The photoluminescence properties are studied as a function of Be2+ doping concentration, and the optimal Be2+ concentration of 0.01 is found. The internal quantum efficiency of 74.9% and external quantum efficiency of 56.3% are achieved under UV excitation, higher than those via co‐doping other divalent metal ions. This study indicates that the addition of Be2+ dominates the charge compensation because Be2+ is closer to Al3+ in size than Mn2+ and other divalent metal ions. The backlight light‐emitting diodes using CAO: Mn4+, Be2+ are fabricated, exhibiting a 110.1% Nation Television Standards Committee (NTSC) color gamut, wider than both the current commercial backlight using K2SiF6: Mn4+ (KSF) red phosphor and the conventional one using YAG yellow phosphor. [ABSTRACT FROM AUTHOR]

Rare-earth doped Ca 2 Al 2 SiO 7 (CAS) phosphors have been widely investigated due to their luminescent properties and low price. However, the luminescence intensity and thermal stability of CAS based phosphors are still not favorable due to rare-earth doping induced vacancies. In this study, to compensate the Ca2+ vacancies by charge unbalanced substitution of Eu3+ in Ca 2 Al 2 SiO 7 : 0.07Eu3+ phosphor, a series of Ca 2 Al 2 SiO 7 : 0.07R, 0.07Eu3+ (R Li+, Na+, K+, Mg2+) phosphors with charge compensators are prepared by sol-gel method. The effects of different charge compensators Li+, Na+, K+, Mg2+ on the phase purity, surface morphology, luminescence properties and thermal stability of the CAS: 0.07Eu3+ phosphors are investigated. It is found that the structures and microstructures of the phosphors are seldom influenced by the co-doped charge compensators R, while the photoluminescence properties are strongly reinforced. Compared with the uncompensated phosphor, all R co-doped samples exhibit remarkable enhancement on luminescence intensity. Among them, Mg2+ compensated phosphor demonstrates the largest enhancement effect with intensity up to 4 times of uncompensated sample. CAS: 0.07 Mg2+, 0.07Eu3+ exhibits a good color purity (87%) with chromaticity coordinates (0.6454, 0.3542), which is very close to the standard red light. Furthermore, the luminous intensity can maintain 76.1% of the initial intensity at 438 K, indicating its excellent thermal stability. These results indicate that charge compensated CAS: Eu3+ phosphors can be used as a candidate material for red phosphor in white LED. [ABSTRACT FROM AUTHOR]

Cobalt phosphide (CoP) is a promising electrocatalyst due to its abundance and excellent stability in alkaline solution. However, its poor conductivity and intrinsic catalytic activity limit its potential in electrochemical water splitting. To address this, a heterogeneous atom doping strategy has been proposed to synthesize magnesium-doped cobalt phosphide nanoneedle arrays, or Mg-doped CoP. Our theoretical calculations show that transition metal Mg atoms doping into the CoP lattice can enhance the electronic structure and modulate the free energy of reacting species, resulting in a significant improvement in the intrinsic catalytic activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) process. The electrochemical tests reveal that the optimal 10% Mg-doped CoP nanoneedle arrays exhibit outstanding HER and OER electrocatalytic activities with overpotential values of 85 and 236 mV at 10 mA/cm2, respectively, outperforming previously reported CoP-based catalysts. This study not only presents a strategy to enhance the catalytic activity of CoP-based materials, but also offers a reference for achieving efficient electrochemical hydrogen production by hydrolysis. [Display omitted] • The charge compensation effect optimizes not only the electronic structure but also the free energy of H∗ and HOO∗ species. • The low-valent Mg2+ ions replace part of the Co3+ sites in the CoP lattice. • The creation of phosphorus vacancies in adjacent sites to maintain electroneutrality. [ABSTRACT FROM AUTHOR]

Lanthanide ions (Yb3+ or Er3+) alloying of CsPb(Cl1‐xBrx)3 quantum dots (QDs) to emit approaching 1000 nm show promise in near‐infrared light‐emitting diodes (NIR‐LEDs). High Yb3+ alloying ratio increases the electroluminance efficiency of emission at 990 nm and enables high external quantum efficiency (EQE) of NIR‐LEDs, however, the high alloying ratio also results in inferior material stability and PLQY drop because of Yb3+‐induced nanocrystal precipitation. This study finds that the heavy alloying of Yb3+ ions causes lattice distortion and coherent energy reduction of Yb3+: CsPb(Cl1‐xBrx)3 QDs, induced by two Yb3+ ions replacing three Pb2+, which leads to the collapse of the octahedral structure in ambient conditions. It posits that spontaneous monovalent ion (Na+) alloying can address the trade‐off between material stability and emission intensity. The Na+ occupies the vacancy of Pb2+ ions, relaxing the distortion in the lattice and improving the phase stability of octahedral structure, and this optimized structure in turn allows a higher Yb3+ alloying ratio. Stability measurements show that the Na+/Yb3+ co‐alloyed films show ten‐fold higher material stability and 2.0‐fold emission efficiency related to controls. It reports that as a result Na+/Yb3+ co‐alloyed NIR‐LEDs have an EQE of 6.4% at 990 nm, which is among the highest perovskite NIR‐LEDs beyond 950 nm. [ABSTRACT FROM AUTHOR]

Chemical substitution, which can be iso- or heterovalent, is the primary strategy to tailor material properties. There are various ways how a material can react to substitution. Isovalent substitution changes the density of states while heterovalent substitution, i.e. doping, can induce electronic compensation, ionic compensation, valence changes of cations or anions, or result in the segregation or neutralization of the dopant. While all these can, in principle, occur simultaneously, it is often desirable to select a certain mechanism in order to determine material properties. Being able to predict and control the individual compensation mechanism should therefore be a key target of materials science. This contribution outlines the perspective that this could be achieved by taking the Fermi energy as a common descriptor for the different compensation mechanisms. This generalization becomes possible since the formation enthalpies of the defects involved in the various compensation mechanisms do all depend on the Fermi energy. In order to control material properties, it is then necessary to adjust the formation enthalpies and charge transition levels of the involved defects. Understanding how these depend on material composition will open up a new path for the design of materials by Fermi level engineering. [ABSTRACT FROM AUTHOR]

Cation‐disordered Rocksalt oxides (DRXs) are a promising new class of cathode materials for Li‐ion batteries due to their natural abundance, low cost and great electrochemical performance. High entropy strategy in Mn‐based DRXs appears to be an effective strategy for improving the rate capability, but it suffers from challenges including capacity degradation. The present paper reports a new group of high entropy DRXs (HE DRX) based on Ni2+‐Nb5+ pair; the structural and chemical evolution upon cycling of DRXs with an increasing transition metal (TM) species are systematically investigated. An explanation is proposed for how the crystal field stability energy determines that HE DRX could exist in single Rocksalt solid solution structures. We further reveal that the charge compensation mechanism in HE DRX is the result of various TM synergistic effect. More importantly, through various in situ and ex situ techniques and theoretical calculation, the effective integration of more TM cation species within the HE DRX framework promotes better Li+ diffusion and improves lattice oxygen stability, consequently increasing capacity upon cycling. [ABSTRACT FROM AUTHOR]

BaSr2(PO4)2: 4 %Eu3+, 4 %A (A = Li+, Na+, K+) phosphors were prepared by high-temperature solid-phase method. The crystal structure, photoluminescence properties, thermal stability, chromaticity coordinates, and fluorescence lifetime of the samples were investigated. The excitation and emission spectra of the samples are broadbands and the maximum peak of the emission spectrum is located at 619 nm. Among three charge compensators, the luminescence intensity is optimal for Li+ co-doping case, and the quenching temperature of the typical sample is about 500 K. the fluorescence lifetime τ is 1469.6 ns, and the chromaticity coordinates exhibit a strong red emission. The present phosphor has a potential application for white light-emitting diodes (LEDs) under the near-ultra violet (n-UV) light excitation. [ABSTRACT FROM AUTHOR]

The low-valence cations Na+ and Sr2+ were selected as the co-dopants to increase the vacancies concentration in the Y2.982Ce0.018Al2Ga3O12 phosphor. The successful incorporation of Na+ and Sr2+ was confirmed by the X-Ray Diffraction (XRD) results. All the samples show 5d-4f green persistent luminescence of Ce3+ after 450 nm excitation. The decay curves demonstrate that the persistent luminescence is effectively enhanced with Na+ and Sr2+ doping. The thermoluminescence glow curves also show not only does the trap concentration increase, but also the distribution of trap depths is broadened. In addition, the air- and H2/Ar-annealing treatments were conducted on every as-made sample. The experimental results prove that the increased traps after the Na+/Sr2+ doping are mainly attributed to the oxygen vacancies, and the traps have a continuous and broad distribution of trap depths. We hope this work could give new inspiration for designing a high-performance persistent phosphor. [ABSTRACT FROM AUTHOR]

Conducting polymers with high theoretical capacitance and deformability are among the optimal candidates for compressible supercapacitor electrode materials. However, achieving both mechanical and electrochemical stabilities in a single electrode remains a great challenge. To address this issue, the "Polymer Chainmail" is proposed with reversible deformation capability and enhances stability because of the steric hindrance and charge compensation effect of doped anions. As a proof of concept, four common anions are selected as dopants for Poly(3,4‐ethylenedioxythiophene) (PEDOT), and their effects on the adsorption and diffusion of H+ on PEDOT are verified using density functional theory calculations. Owing to the film formation effect, the PF6- ${{\rm{PF}}_6^- }$ doped PEDOT/nitrogen‐doped carbon foam exhibits good mechanical properties. Furthermore, the composite demonstrates excellent rate performance and stability due to suitable anion doping. This finding provides new insights into the preparation of electrochemically stable conductive polymer‐based compressible electrode materials. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) light sources have great potential in applications such as optical imaging, non-destructive medical diagnosis, and non-visual lighting. Ni2+ activated phosphors as a class of newly discovered NIR emitting material shows broadband luminescent properties that covers NIR-II (1000–1600 nm) region which is relatively transparent and less scattering in tissues. However, it has shortcomings, such as low luminous efficiency and poor thermal stability that need to be improved. Here, we report the synthesis of new Ni2+-activated SrTiO 3 perovskite-based broadband NIR phosphor by high-temperature solid-state reaction method, with M5+ (M = Ta, Sb, Nb, P) as the co-doping agent to compensate charges. By charge compensation, the new composition significantly improved the NIR emission intensity by 12 folds, increased the luminescence quantum efficiency from 7.9% to 19.7%, and improved the resistance to thermal quenching. We studied the synergistic effect of charge compensation on the luminescence performance of NIR phosphor by experimental and simulation approaches. We showed that co-doping of charge compensator improved NIR phosphors by eliminating electronic defects and introducing defect or distortion to lattice octahedra. We further demonstrate that NIR pc-LED can be made by packaging the optimized NIR phosphor with a UV LED chip. Its potential application in the field of optical imaging was discussed. [ABSTRACT FROM AUTHOR]

A series of Mn4+‐doped and Mn4+,K+‐co‐doped Ba2LaTaO6 (BLT) double‐perovskite phosphors was synthesized using a high‐temperature solid‐state reaction. The phase purity and luminescence properties were also studied. The optimum doping concentration of Mn4+ and K+ was obtained by investigating the photoluminescence excitation spectra and photoluminescence emission spectra. The comparison of BLT:Mn4+ phosphors with and without K+ ions shows that the photoluminescence intensity of K+‐doped phosphors was greatly enhanced. This is because there was a charge difference when Mn4+ ions were doped with Ta5+ ions in BLT. Mn4+–K+ ion pairs were formed after doping K+ ions, which hinders the nonradiative energy transfer between Mn4+ ions. Therefore, the luminescence intensity, quantum yield, and thermal stability of phosphors were enhanced. The electroluminescence spectra of BLT:Mn4+ and BLT:Mn4+,K+ were measured. The spectra showed that the light emitted from the phosphors corresponded well with chlorophyll a and phytochrome PR. The results show that the BLT:Mn4+,K+ phosphors had good luminescence properties and application prospects and are ideal materials for plant‐illuminated red phosphors. [ABSTRACT FROM AUTHOR]

A mixed-signal four-channel biphasic current-mode functional electrical stimulator chip with a novel charge compensation circuit is presented in this paper. This chip can induce programmable biphasic current ranging from 10 μ A to 2.56 mA for each channel. However, a significant problem with functional electrical stimulation is charge balancing (CB) due to anodic and cathodic current mismatch for process variation. Therefore, a novel compensation module including both passive and active charge compensation schemes are adopted in this chip. The charge compensation module autonomously adjusts the supply and compensation current to achieve fast compensation and low-power consumption simultaneously. The proposed biphasic stimulator is designed and fabricated in a 0.18 μ m CMOS process with a die area of 2.27 mm × 1.99 mm. The measurement results from a test bench demonstrate the proposed circuit functionalities, and the standby power consumption of this chip is 193.7 μ W. Besides, animal experiments on mice for seizure suppression with deep brain stimulation were performed to verify the efficacy and safety of the developed stimulation chip. • A biphasic current-mode electrical stimulator with charge compensation is presented. • A novel module including both passive and active charge compensation schemes is adopted in this chip. • The proposed biphasic stimulator is designed and fabricated in a 0.18 μ m CMOS process. • Fast residual charge compensation and low power consumption module implemented. • Animal experiments were performed to verify the efficacy and safety of the developed stimulator. [ABSTRACT FROM AUTHOR]

A series of Sr3Bi(PO4)3:Sm3+ phosphors co-doped with alkali metal A+ (A = K+, Na+ and Li+) ions were synthesized using a wet chemical technique. XRD, morphological, and photoluminescence characteristics were all measured and investigated in detail. The XRD results confirm that Sr3Bi(PO4)3 has a cubic phase and is in the space group I −4 3 d. (220). Under 403 nm excitation, the Sr3Bi(PO4)3:Sm3+ phosphor showed maximum emission at 598 nm. The emission bands were at 562 nm, 598 nm, and 643 nm when stimulated at 403 nm. The optimal Sm3+ ions doping concentration in the Sr3Bi(PO4)3 host matrix is determined to be 0.5 mol %. Furthermore, A+ (A = K+, Na+ and Li+) as the charge compensation co-doped with Sr3Bi(PO4)3:Sm3+ phosphors increases emission intensity, and Sr3Bi(PO4)3:Sm3+, K+ phosphors shows the maximum emission intensity. According to the CIE coordinates of the Sr3Bi(PO4)3:Sm3+, K+ phosphors were (x = 0.617, y = 0.381). The results show that Sr3Bi(PO4)3:Sm3+, K+ phosphors may have been used in w-LEDs.

Lead zirconate titanate (PZT) films with high Nb concentrations (6–13 mol%) were grown by chemical solution deposition. In concentrations up to 8 mol% Nb, the films self-compensate the stoichiometry; single phase films were grown from precursor solutions with 10 mol% PbO excess. Higher Nb concentrations induced multi-phase films unless the amount of excess PbO in the precursor solution was reduced. Phase pure perovskite films were grown with 13 mol% excess Nb with the addition of 6 mol% PbO. Charge compensation was achieved by creating lead vacancies when decreasing excess PbO level; using Kroger-Vink notation, N b T i • are ionically compensated by V P b ″ to maintain charge neutrality in heavily Nb-doped PZT films. With Nb doping, films showed suppressed {100} orientation, the Curie temperature decreased, and the maximum in the relative permittivity at the phase transition broadened. The dielectric and piezoelectric properties were dramatically degraded due to increased quantity of the non-polar pyrochlore phase in multi-phase films; ε r reduced from 1360 ± 8 to 940 ± 6, and the remanent d33,f value decreased from 112 to 42 pm/V when increasing the Nb concentration from 6 to 13 mol%. Property deterioration was corrected by decreasing the PbO level to 6 mol%; phase pure perovskite films were attained. εr and the remanent d33,f increased to 1330 ± 9 and 106 ± 4 pm/V, respectively. There was no discernable difference in the level of self-imprint in phase pure PZT films with Nb doping. However, the magnitude of the internal field after thermal poling at 150 °C increased significantly; the level of imprint was 30 kV/cm and 11.5 kV/cm in phase pure 6 mol% and 13 mol% Nb-doped films, respectively. The absence of mobile V O • • , coupled with the immobile V P b ″ in 13 mol% Nb-doped PZT films, leads to lower internal field formation upon thermal poling. For 6 mol% Nb-doped PZT films, the internal field formation was primarily governed by (1) the alignment of (V P b ″ − V O • •  ) x and (2) the injection and subsequent electron trapping by Ti4+. For 13 mol% Nb-doped PZT films, hole migration between V P b ″ controlled internal field formation upon thermal poling. [ABSTRACT FROM AUTHOR]