Synergic effects of Cu_xO electron transfer co-catalyst and valence band edge control over TiO_2 for efficient visible-light photocatalysis

Bandgap engineering by doping and co‐catalyst loading are two primary approaches to designing efficient photocatalysts by promoting visible‐light absorption and charge separation,respectively.Shifting of the TiO2conduction band edge is frequently applied to increase visible‐light absorption but also lowers the reductive properties of photo‐excited electrons.Herein,we report a visible‐light‐driven photocatalyst based on valance band edge control induced by oxygen excess defects and modification with a CuxO electron transfer co‐catalyst.The CuxO grafted oxygen‐rich TiO2microspheres were prepared by ultrasonic spray pyrolysis of the peroxotitanate precursor followed by a wet chemical impregnated treatment.We found that oxygen excess defects in TiO2shifted the valence band maximum upward and improved the visible‐light absorption.The CuxO grafted onto the surface acted as a co‐catalyst that efficiently reduced oxygen molecules to active intermediates(i.e.,O2??radial and H2O2),thus consuming the photo‐generated electrons.Consequently,the CuxO grafted oxygen‐rich TiO2microspheres achieved a photocatalytic activity respectively8.6,13.0and11.0as times high as those of oxygen‐rich TiO2,normal TiO2and CuxO grafted TiO2,for degradation of gaseous acetaldehyde under visible‐light irradiation.Our results suggest that high visible‐light photocatalytic efficiency can be achieved by combining oxygen excess defects to improve visible‐light absorption together with a CuxO electron transfer co‐catalyst.These findings provide a new approach to developing efficient heterojunction photocatalysts.

Regulation of photophysical and electronic properties of I-III-VI quantum dots for light-emitting diodes

Quantum dot light-emitting diodes(QLEDs)have become an important research direction in the pursuit of next-generation display technology owing to their favorable attributes,including high energy efficiency,wide color gamut,and low cost.Breakthroughs in the luminous efficiency and operating life of QLEDs have been achieved by enhancing the photoluminescence efficiency of the quantum dots(QDs)and optimizing the device structure.However,the current mainstream QDs contain heavy metal elements such as lead and cadmium,which restrict the development and application of QD displays.Exploring new types of environmentally friendly QDs is crucial.I-III-VI semiconductor QDs have been developed as luminescent materials for constructing high color rendering index QLEDs,owing to the outstanding photophysical properties of these QDs,such as composition-dependent tunable bandgap,large Stokes shift,and highefficiency luminescence.Currently,the microstructures of heterojunctions,especially the surface states and interface states,affect the recombination and transport of carriers in electroluminescent(EL)devices with multilayer thin film structures,which in turn influence the luminous efficiency and stability of the device.This review focuses on the synthesis strategies of I-III-VI multi-component QDs and provides an in-depth understanding of the luminescence mechanism and the regulation of photophysical and electronic properties.Furthermore,the application of I-III-VI QDs in multi-color and white EL QLEDs is discussed and the challenges and outlook are addressed.

Influences of La and Ce doping on giant magnetocaloric effect of EuTiO

Giant reversible magnetocaloric effects and magnetic properties in Euo.9Ro.lTiO3 （R = La, Ce） are investigated. The antiferromagnetic ordering of pure EuTiO3 can significantly change to be ferromagnetic as substitution of La （x = 0.1） and Ce （x = 0.1） ions for Eu2＋ ions. The values of -ASM and RC are evaluated to be 10.8 J/（kg.K） and 51.8 J/kg for Euo.gCeo.lTiO3 and 11 J/（kg.K） and 39.3 J/kg for Euo.9Lao.lTiO3 at a magnetic field change of I0 kOe, respectively. The large low-field enhancements of --ASM and RC can be attributed to magnetic phase transition. The giant reversible MCE and large RC suggest that Euo.9Ro.ITiO3 （R = La, Ce） compounds could be promising materials in low temperature and low magnetic field refrigerants.

Influence of Al^(3+) doping on the energy levels and thermal property of the 3.5MgO·0.5MgF_2·GeO_2:Mn^(4+) red-emitting phosphor

A series of Al3+-doped 3.5MgO·0.5MgF2·GeO2:Mn4+red-emitting phosphors is synthesized by high temperature solid-state reaction. The broad excitation band at 300 nm–380 nm, resulting from the4A2→4T1transition of Mn4+,exhibits a blue shift with the increase of Al2O3 content. The observation of the decreased Mn4+–O2-distance is explained by the crystal field theory. The temperature-dependent photoluminescence spectra with various amounts of Al2O3 content are comparatively measured and the calculation shows that the activation energy increases up to 0.41 eV at the Al2O3 content of 0.1 mol. The maximum phonon densities of state for these samples are calculated from Raman spectra and they are correlated with the thermal properties.

Giant low-field magnetocaloric effect in EuTi(1-x)NbxO3(x = 0.05, 0.1, 0.15, and 0.2) compounds

The magnetic properties and magnetocaloric effect(MCE)of EuTi(1-x)NbxO3(x=0.05,0.1,0.15,and 0.2)compounds are investigated.Owing to electronic doping,parts of Ti ions are replaced by Nb ions,the lattice constant increases and a small number of Ti^(4+)(3d^0)ions change into Ti^(3+)(3d^1).It is the ferromagnetism state that is dominant in the derivative balance.The values of the maximum magnetic entropy change(-?SM^(max))are 10.3 J/kg·K,9.6 J/kg·K,13.1 J/kg·K,and 11.9 J/kg·K for EuTi(1-x)NbxO3(x=0.05,0.1,0.15,and 0.2)compounds and the values of refrigeration capacity are 36,33,86,and 80 J/kg as magnetic field changes in a range of 0 T–1 T.The EuTi(1-x)NbxO3(x=0.05,0.1,0.15,and 0.2)compounds with giant reversible MCE are considered as a good candidate for magnetic refrigerant working at lowtemperature and low-field.

Effect of chloride introduction on the optical properties in Eu^(3+)-doped fluorozirconate glasses

Fluorozirconate glass containing Euions and chloride ions are prepared by a meltquenching method. The luminescence behavior of Euaffected by Cl ions is investigated. With increasing Cl ion concentration, the luminous intensity of Euis significantly enhanced and the quantum efficiency of fluorozirconate glass is improved. Meanwhile, the intensity parameter ?increases according to the Judd–Ofelt calculation, which indicates the decrease of local symmetry. The average lifetime of Euincreases by introducing the Cl ions. Moreover, we find two kinds of sites for Euions in a glass network by analyzing the fluorescence decay. The distribution of Euions changes with increasing Cl ion concentration.In addition, the excessive Cl ions lead to the separation of the glass phase and the formation of the crystal phase, thus reducing the transmittance dramatically.

Improvement of the low-field-induced magnetocaloric effect in EuTiO3 compounds

The magnetocaloric effect of Mn,Ni,and Mn-Ni-doped EuTiO3 compounds are studied in the near-liquid-helium-temperature range.The Eu(Ti0.9375Mn0.0625)O3,Eu(Ti0.975Ni0.025)O3,and Eu(Ti0.9125Mn0.0625Ni0.025)O3 are prepared by the sol-gel method.The Eu(Ti0.9375Mn0.0625)O3 and Eu(Ti0.9125Mn0.0625Ni0.025)O3 exhibit ferromagnetism with second-order phase transition,and the Eu(Ti0.975Ni0.025)O3 displays antiferromagnetic behavior.Under the magnetic field change of 10 kOe(1 Oe=79.5775 Am-1),the values of magnetic entropy change are 8.8 Jkg-1K-1,12 Jkg-1K-1,and 10.9 Jkg-1K-1 for Eu(Ti0.9375Mn0.0625)O3,Eu(Ti0.975Ni0.025)O3,and Eu(Ti0.9125Mn0.0625Ni0.025)O3,respectively.The co-substitution of Mn and Ni can not only improve the magnetic entropy change,but also widen the refrigeration temperature window,which greatly enhances the magnetic refrigeration capacity.Under the magnetic field change of 10 kOe,the refrigerant capacity value of Eu(Ti0.9125Mn0.0625Ni0.025)O3 is 62.6 Jkg-1 more than twice that of EuTiO3(27 Jkg-1),indicating that multi-component substitution can lead to better magnetocaloric performance.

Observation of giant magnetocaloric effect under low magnetic fields in EuTi_(1-x)Co_xO_3

The magnetic properties and magnetocaloric effect（MCE） in EuTi1-xCoxO3（x = 0, 0.025, 0.05, 0.075, 0.1） compounds have been investigated. When the Ti^4＋ ions were substituted by Co2＋ions, the delicate balance was changed between antiferromagnetic（AFM） and ferromagnetic（FM） phases in the EuTiO3 compound. In EuTi1-xCoxO3 system, a giant reversible MCE and large refrigerant capacity（RC） were observed without hysteresis. The values of -△SM^max were evaluated to be around 10 J·kg^-1·K^-1 for EuTi0.95Co0.05O3 under a magnetic field change of 10 kOe. The giant reversible MCE and large RC suggests that EuTi1-xCoxO3 series could be considered as good candidate materials for low-temperature and low-field magnetic refrigerant.

Synthesized few-layers hexagonal boron nitride nanosheets

The hexagonal boron nitrides （BNs） with different morphologies are synthesized on a large scale by a simple route using a two-step synthetic process. The morphology of h-BN can be easily controlled by changing the heat-treatment atmosphere. The whiskers with 0.5-10 μm in diameter and 50-100 μm in length consist of few-layers nanosheets in the NH3 gas. The BN nanosheets can be dissociated from the whiskers by ultrasonic treatment, which are less than 5 nm in thickness and even only two layers thick. The concentration and activity of N play an important rule, and abundant N and higher activity are conducive for refining grain in reaction. The H3BO3 and C3N6H6 molecules form a layer-like morphology with the interlinked planar triangle by a hydrogen-bonded structure.

Effects of 1,9-dibromnonane on the structural, photophysical properties and stability of cesium lead bromide perovskite nanocrystals

The CsPbBr3@Cs4PbBr6 nanocrystals(NCs) could be synthesized by multiple Cs-oleate injections as adding the 1,9-dibromnonane in the reaction solution. The 1,9-dibromnonane could provide Br-ions and the rich Br-ions effectively restrain the generation of Cs Br. The Cs4 PbBr6 wrapped around the Cs Pb Br3 NCs and the size of crystalline grain was increased with increasing the Cs-oleate as excess oleylamine. The quantum yield for 14 S4 DN reached to 99.3% due to the decrease of defects and the surface passivation of Cs4 PbBr6. There are more oleylammonium bromide on the surface of Cs Pb Br3 NCs as synthesized with1,9-dibromnonane. The ligand shell and the surface passivation of Cs4 PbBr6 restrained the decomposition of surface, consequently improved the stability of moisture and light for Cs Pb Br3 NCs. When the CsPbBr3@Cs4PbBr6 NCs were immersed in water under UV light(365 nm) for 2 h, the PL intensity could retain 90.4%, while the 11 S1(traditional Cs Pb Br3 NCs) was only 10.9%. It indicated the stability of moisture and light for Cs Pb Br3 NCs were greatly improved, because Cs4 PbBr6 NCs effectively passivated the surface of Cs Pb Br3 NCs and restrained the generation of traps states.

White emission from Tm^(3+)/Tb^(3+)/Eu^(3+) co-doped fluoride zirconate under ultraviolet excitation

We synthesize Tm3＋/Tb3＋/Eu3＋ triply-doped ZrF4-BaF2-LaF3-A1F3-NaF （ZBLAN） transparent glass by using a melt-quenching method. Under excitation of 365 nm, the white emission with Commission internationale deL＇Eclairage （CIE） coordinates of （0.33, 0.33） is achieved at the Eu3＋ concentration of 1.1 mol%. The mechanisms for white emission and the energy transfer process of Tb3＋→ Eu3＋ are discussed in terms of the photoluminescence, photoluminescence excitation spectra, and the light emission decay curves. The nature for the Tb3＋ → Eu3＋ energy transfer is described with the aid of an energy level diagram.

Nd^(3+) doped fluorochlorozirconate glass: 3.9 μm MIR emission properties and energy transfer

The Nd^(3+) doped fluorochlorozirconate(FCZ) glass was prepared by melt-quenching method. The 3.9 μm emission from Nd^(3+) ions is attributed to the two-photon absorption process. The strong emission transition at 3.9 μm fluorescence peak intensity, corresponding to the ~4G_(11/2)→~2K_(13/2) transition, is directly proportional to the NaCl concentration. With the increase of the Cl-ions amount, the mid-infrared(MIR) luminescent intensity is significantly enhanced. Additionally, the Judd-Ofelt(J-O) parameter ?_2 is larger than that of the fluorozirconate(FZ) glass, which indicates the covalency of the bond between RE ions and ligand is stronger as Cl-ions substitution of F-ions in chloride FZ glass. The X-ray diffraction(XRD) patterns show that the amorphous glassy state keeps the FZ glass network structure. In brief, the advantageous spectroscopic characteristics make the Nd^(3+)-doped FCZ glass be a promising candidate for application of 3.9 μm emission.