Ionic Interactions in Molecular and Liquid States ofPolyvalent Metal Halides

Progress in the development of phenomenological models for the microscoplc interactions in the halides of polyvalent metals is reviewed, with main attention to neutral and ionized molecular states and to the melts of these materials. The following physical problems are discussed: (1)bond bending in the molecules of the alkaline-earth halides, (2) binding of molecular dimers and halogen transfer reactions relevant to the melts of trivalent metal halides, (3) stability of molecular ions in liquid mixtures of polyvalent metal halides and alkali halides, and (4) stabilityof molecular ions and reduced-valence states in molten cryolite under addition of sodium metal.

Realizing efficient emission and triple-mode photoluminescence switching in air-stable tin(IV)-based metal halides via antimony doping and rational structural modulation

Recently,many lead-free metal halides with diverse structures and highly efficient emission have been reported.However,their poor stability and single-mode emission color severely limit their applications.Herein,three homologous Sb^(3+)-doped zero-dimensional(0D)air-stable Sn(IV)-based metal halides with different crystal structures were developed by inserting a single organic ligand into SnCl_(4)lattice,which brings different optical properties.Under photoexcitation,(C_(25)H_(22)P)SnC_(l5)@Sb⋅CH_(4O)(Sb^(3+)−1)does not emit light,(C_(25)H_(22)P)_(2)SnC_(l6)@Sb-α(Sb^(3+)−2α)shines bright yellow emission with a photoluminescence quantum yield(PLQY)of 92%,and(C_(25)H_(22)P)_(2)SnC_(l6)@Sb-β(Sb^(3+)−2β)exhibits intense red emission with a PLQY of 78%.The above three compounds show quite different optical properties should be due to their different crystal structures and the lattice distortions.Particularly,Sb^(3+)−1 can be successfully converted into Sb^(3+)−2αunder the treatment of C_(25)H_(22)PCl solution,accompanied by a transition from nonemission to efficient yellow emission,serving as a“turn-on”photoluminescence(PL)switching.Parallelly,a reversible structure conversion between Sb^(3+)−2αand Sb^(3+)−2βwas witnessed after dichloromethane or volatilization treatment,accompanied by yellow and red emission switching.Thereby,a triple-mode tunable PL switching of off-onI-onII can be constructed in Sb^(3+)-doped Sn(IV)-based compounds.Finally,we demonstrated the as-synthesized compounds in fluorescent anticounterfeiting,information encryption,and optical logic gates.

Highly stable metal halides Cs_(2)ZnX_(4)(X = Cl, Br) with Sn2+ as dopants for efficient deep-red photoluminescence

The development of deep-red emitting lead-free metal-halide perovskites with high photoluminescence quantum yields (PLQYs) and outstanding stability remains a major challenge for displays and deep-tissue bioimaging.In this work,we report a facile and convenient solvothermal method to synthesize metal halides Cs_(2)Zn X_(4)(X=Cl,Br) that however is PL innert at room temperature.Upon composition engineering utilizing Sn^(2+) as the dopant,the resulting Cs_(2)Zn Cl_(4):Sn not only emits strong deep-red PL peaked at700 nm with the highest 99.4%PLQY among the similar materials so far,but also exhibits excellent structure stability in air (PLQY remains 96%after one year exposure to the atmosphere).Detailed experimental characterizations and theoretical calculations reveal that the deep-red emission stems from self-trapped excitons induced by the Sn^(2+) dopant.Particularly,triplet emission (^(3)P_(2)→^(1)S_(0)) from Sn-5s^(2) orbitals has been observed at low temperature due to the break of parity-forbidden transition.This work provides an important guidance for the development of deep-red light-emitting materials with low price,high efficiency and excellent stability.

Copper‑based metal halides for X‑ray and photodetection

Copper-based metal halides have become important materials in the feld of X-ray and photodetection due to their excellent optical properties,good environmental stability and low toxicity.This review presents the progress of research on crystal structure/morphology,photophysics/optical properties and applications of copper-based metal halides.We also discuss the challenges of copper-based metal halides with a perspective of their future research directions.

Self-trapped exciton emission in inorganic copper(Ⅰ)metal halides

The broad emission and high photoluminescence quantum yield of self-trapped exciton(STE)radiative recombination emitters make them an ideal solution for single-substrate,white,solid-state lighting sources.Unlike impurities and defects in semiconductors,the formation of STEs requires a lattice distortion,along with strong electron–phonon coupling,in low electrondimensional materials.The photoluminescence of inorganic copper(Ⅰ)metal halides with low electron-dimensionality has been found to be the result of STEs.These materials were of significant interest because of their leadfree,all-inorganic structures,and high luminous efficiencies.In this paper,we summarize the luminescence characteristics of zero-and one-dimensional inorganic copper(I)metal halides with STEs to provide an overview of future research opportunities.

Optoelectronic and elastic properties of metal halides double perovskites Cs_(2)InBiX_(6)(X = F, Cl, Br, I)

Structural geometry, electronic band gaps, density of states, optical and mechanical properties of double perovskite halides Cs2InBiX6(X = F, Cl, Br, I) are investigated using the density functional theory. These compounds possess genuine perovskite stoichiometry, evaluated using various geometry-based indices like tolerance factor, octahedral factor, and formation energy. The fundamental electronic band gaps are direct and valued in the range 0.80–2.79 e V. These compounds have narrow band gaps(except Cs2InBiX6) due to strong orbital coupling of the cations. The valence band maximum and conduction band minimum are confirmed to be essentially of In 5 s and Bi 6 p characters, respectively. The splitting of Bi 6 p bands due to strong spin-orbit coupling causes reduction in the band gaps. These compounds have large dispersion in their bands and very low carrier effective masses. The substitution of halogen atoms has great influence on the optical properties. The mechanical properties reveal that Cs2InBiX6(X = F, Cl, Br, I) satisfy the stability criteria in cubic structures.

Enthalpic Interaction for α-Amino Acid with Alkali Metal Halides in Water

The studies of the enthalpic interaction parameters, hxy, hxyy and hxxy, of alkali metal halides with glycine, α-alanine and α-aminobutyric acid were published. Synthetic considering of the results of the studies, some inter- esting behaviors of the interaction between alkali metal halides and the α-amino acids have been found. The values of hxywill increase with the increase of the number of carbon atoms in alkyl side chain of amino acid molecules and decrease with the increase of the radius of the ions. The increasing of the salt’s effect on the hydrophobic hydration structure as the radii of anion is more obvious than as that of cation. The value of hxxy will regularly decrease with the increase of the number of carbon atoms in the alkyl chain of amino acids and linear increase with the increase of the radius. But the relation of hxxywith the radius of cations is not evident. The value of hxyywill increase with the increase of the radii of the ions. As the increase of the number of carbon atoms of amino acids, hxyyis decreas for the ions which have lager size and there is a maximum value at α-alanine for the ions which have small size. The behaviors of the interaction mentioned above were further discussed in view of electrostatic and structural interac- tions.

Regioselective halide attack on 2,3-epoxyalcohols by complex metal halides

Owing to the importance of Sharpless epoxidation reaction in asymmetric synthesis,the regio-and stereoselective opening of the resulting 2, 3-epoxyalcohols has become a topicof current interest.Although many nucleophiles attack Cin high selectivity under the actionof Ti（OR）4,some of them like halides, azide, and cyanide only show moderate propensity

Infrared optical absorption of Fr?hlich polarons in metal halide perovskites

The formation of Frohlich polarons in metal halide perovskites,arising from the charge carrier-longitudinal optical(LO)phonon coupling,has been proposed to explain their exceptional properties,but the effective identification of polarons in these materials is still a challenging task.Herein,we theoretically present the infrared optical absorption of Frohlich polarons based on the Huang-Rhys model.We find that multiphonon overtones appear as the energy of the incident photons matches the multiple LO phonons,wherein the average phonon number of a polaron can be directly evaluated by the order of the strongest overtone.These multiphonon structures sensitively depend on the scale of electronic distribution in the ground state and the dimensionality of the perovskite materials,revealing the effective modulation of competing processes between polaron formation and carrier cooling.Moreover,the order of the strongest overtone shifts to higher ones with temperature,providing a potential proof that the carrier mobility is affected by LO phonon scattering.The present model not only suggests a direct way to verify Frohlich polarons but also enriches our understanding of the properties of polarons in metal halide perovskites.

Self-assembly of perovskite nanocrystals:From driving forces to applications

Self-assembly of metal halide perovskite nanocrystals(NCs)into superlattices can exhibit unique collective properties,which have significant application values in the display,detector,and solar cell field.This review discusses the driving forces behind the self-assembly process of perovskite NCs,and the commonly used self-assembly methods and different self-assembly structures are detailed.Subsequently,we summarize the collective optoelectronic properties and application areas of perovskite superlattice structures.Finally,we conclude with an outlook on the potential issues and future challenges in developing perovskite NCs.

Flexible perovskite light-emitting diodes for display applications and beyond

The flexible perovskite light-emitting diodes(FPeLEDs),which can be expediently integrated to portable and wearable devices,have shown great potential in various applications.The FPeLEDs inherit the unique optical properties of metal halide perovskites,such as tunable bandgap,narrow emission linewidth,high photoluminescence quantum yield,and particularly,the soft nature of lattice.At present,substantial efforts have been made for FPeLEDs with encouraging external quantum efficiency(EQE)of 24.5%.Herein,we summarize the recent progress in FPeLEDs,focusing on the strategy developed for perovskite emission layers and flexible electrodes to facilitate the optoelectrical and mechanical performance.In addition,we present relevant applications of FPeLEDs in displays and beyond.Finally,perspective toward the future development and applications of flexible PeLEDs are also discussed.

Temperature-dependent self-trapped exciton emission in Cu(I) doped zinc-based metal halides from well-resolved excited state structures

Zero-dimensional metal halides are of unique structures and tunable photoluminescence properties,showing great potential applications such as light-emitting diodes(LEDs)and sensing.Herein,we successfully synthesized Cu^(+)doped(MA)_(2)ZnCl_(4)metal halides by a slow evaporation solvent method.The introduction of Cu^(+)results in sky-blue self-trapped exciton emission in(MA)_(2)ZnCl_(4) at 486 nm at room temperature,and a photoluminescence quantum yield is as high as 54.9%.Interestingly,at low temperatures,Cu^(+)-doped(MA)_(2)ZnCl_(4) exhibits two emission peaks located at 482 and 605 nm,respectively.This temperaturedependent dual emission indicates two excited state structures that exist on the triplet excited-state potential energy surface.In addition,the temperature sensor we fitted has good performance(Sr=1.65%·K^(−1)),which is the first attempt in Cu^(+) doped Znbased metal halides.Our work enriches the family of sky-blue metal halides and provides a promising strategy for building skyblue LEDs.

Recent advances in metal halide perovskite photocatalysts:Properties,synthesis and applications

As a class of new emerged semiconductors,MHPs exhibit many excellent photoelectronic properties,which are superior to most conventional semiconductor nanocrystals(NCs).Particularly,MHPs have received extensive attention and brought new opportunities for the development of photocatalysis.Over the past few years,numerous efforts have been made to design and prepare MHP-based materials for a wide range of applications in photocatalysis,ranging from photocatalytic H_(2) generation,photocatalytic CO_(2) reduction,photocatalytic organic synthesis and pollutant degradation.In this review,recent advances in the development of MHP-based materials are summarized from the standpoint of photocatalysis.A brief outlook of this field has been proposed to point out some important challenges and possible solutions.This review suggests that the new family of MHP photocatalysts provide a new paradigm in efficient artificial photosynthesis.

Strategies and methods for fabricating high quality metal halide perovskite thin films for solar cells

With the development of human society,the problems of environmental deterioration and energy shortage have become increasingly prominent.In order to solve these problems,metal halide perovskite solar cells(PSCs)stand out because of their excellent properties(i.e.,high optical absorption coefficient,long carrier lifetime and carrier diffusion length,adjustable band gap)and have been widely studied.PSCs with low cost,high power conversion efficiency and high stability are the future development trend.The quality of perovskite film is essential for fabricating PSCs with high performance.To provide a full picture of realizing high performance PSCs,this review focuses on the strategies for preparing high quality perovskite films(including antisolvent,Lewis acid-base,additive engineering,scaleable fabrication,strain engineering and band gap adjustment),and therefore to fabricate high performance PSCs and to accelerate the commercialization.

Study on Thermal Expansion Coefficient of Sealing Materials for Ceramic Metal Halide Lamps

With Al2O3, Dy2O3, and SiO2 as starting materials, the basic glass of Al2O3-Dy2O3-SiO2 system was prepared by conventional melting technology, and their thermal expansion coefficients （TECs） at different anneal time were investigated. TECs of the basic glass, which were heat-treated under different temperature, were also investigated. The result showed that TECs of the basic glass gradually approached a fixed value as the anneal time was extended, which suggested that most of the inner stress had been eliminated. After heat treatment, the contents of Dy2O3, Dy2Si2O7, and a new crystal increased up to 1200 ℃ and decreased below 1250 ℃, which was consistent with the TEC change of crystallized samples. This suggests that the crystal has a direct effect on TECs of the crystallized samples.

Near-unity quantum yield in zero-dimensional lead-free manganese-based halides for flexible X-ray imaging with high spatial resolution

Low-dimensional luminescent lead-free metal halides have received substantial attention due to their unique optoelectronic properties.Among them,zero-dimensional(0D)manganese(II)-based metal halides with negligible self-absorption have emerged as potential candidates in X-ray scintillators.Herein,we for the first time report a novel lead-free(TBA)_(2)MnBr_(4) single crystal synthesized via a facile solvent evaporation method.In this crystal,[MnBr_(4)]^(2-)units are isolated by large TBA^(+)organic cations,resulting in a unique 0D structure.The prepared manganese-based crystals exhibit a bright-green emission centered at 512 nm with a high photoluminescence quantum yield(PLQY)of 93.76%at room temperature,originating from the ^(4)T_(1)–^(6)A_(1) transition of Mn^(2+).Apart from their outstanding optical performance,the crystals also show excellent stability and can maintain 94.4%of the initial PLQY even after being stored in air for 90 days.Flexible(TBA)_(2)MnBr4 films prepared as X-ray imaging scintillators exhibit a low detection limit of 63.3 nGyair/s,a high light yield of 68000 ph/MeV,and a high spatial resolution of 15.4 lp/mm.Thus,this work not only enriches the family of lead-free metal halides but also expands the application of manganese(II)-based halides in flexible X-ray scintillators.

Low-Dimensional Halide Perovskites and Their Advanced Optoelectronic Applications

Metal halide perovskites are crystalline materials originally developed out of scientific curiosity. They have shown great potential as active materials in optoelectronic applications. In the last 6 years, their certified photovoltaic efficiencies have reached 22.1%. Compared to bulk halide perovskites, low-dimensional ones exhibited novel physical properties. The photoluminescence quantum yields of perovskite quantum dots are close to 100%. The external quantum efficiencies and current efficiencies of perovskite quantum dot light-emitting diodes have reached 8% and 43 cd A^(-1),respectively, and their nanowire lasers show ultralow-threshold room-temperature lasing with emission tunability and ease of synthesis. Perovskite nanowire photodetectors reached a responsivity of 10 A W^(-1)and a specific normalized detectivity of the order of 10^(12 )Jones. Different from most reported reviews focusing on photovoltaic applications, we summarize the rapid progress in the study of low-dimensional perovskite materials, as well as their promising applications in optoelectronic devices. In particular, we review the wide tunability of fabrication methods and the state-of-the-art research outputs of low-dimensional perovskite optoelectronic devices. Finally, the anticipated challenges and potential for this exciting research are proposed.

Efficient Carbon-Based CsPbBr_3 Inorganic Perovskite Solar Cells by Using Cu-Phthalocyanine as Hole Transport Material

Metal halide perovskite solar cells(PSCs) have attracted extensive research interest for next-generation solution-processed photovoltaic devices because of their high solar-to-electric power conversion efficiency(PCE)and low fabrication cost. Although the world's best PSC successfully achieves a considerable PCE of over 20% within a very limited timeframe after intensive efforts, the stability, high cost, and up-scaling of PSCs still remain issues. Recently, inorganic perovskite material, CsPbBr_3, is emerging as a promising photo-sensitizer with excellent durability and thermal stability, but the efficiency is still embarrassing. In this work, we intend to address these issues by exploiting CsPbBr_3 as light absorber, accompanied by using Cu-phthalocyanine(CuPc) as hole transport material(HTM) and carbon as counter electrode. The optimal device acquires a decent PCE of 6.21%, over 60% higher than those of the HTM-free devices. The systematic characterization and analysis reveal a more effective charge transfer process and a suppressed charge recombination in PSCs after introducing CuPc as hole transfer layer. More importantly, our devices exhibit an outstanding durability and a promising thermal stability, making it rather meaningful in future fabrication and application of PSCs.

Progress on the controllable synthesis of all-inorganic halide perovskite nanocrystals and their optoelectronic applications

In the past five years,all-inorganic metal halide perovskite(CsPbX3,X=Cl,Br,I)nanocrystals have been intensely studied due to their outstanding optical properties and facile synthesis,which endow them with potential optoelectronic applications.In order to optimize their physical and chemical properties,different strategies have been developed to realize the controllable synthesis of CsPbX3 nanocrystals.In this short review,we firstly present a comprehensive and detailed summary of existed synthesis strategies of CsPbX3 nanocrystals and their analogues.Then,we introduce the regulations of several reaction parameters and their effects on the morphologies of CsPbX3 nanocrystals.At the same time,we provide stability improvement methods and representative applications.Finally,we propose the current challenges and future perspectives of the promising materials.

Study on thermal expansion behavior of Dy_2O_3-Al_2O_3-SiO_2 glass

Employing Dy2O3, Al2O3, and SiO2 as starting materials, several series of Dy2O3-Al2O3-SiO2 sealing glass were prepared. The relationship between their coefficients of thermal expansion and the contents of Dy2O3, Al2O3, and SiO2 were studied respectively. Experimental results showed that Dy2O3 and Al2O3 had a positive effect on the coefficient of thermal expansion of glass, whereas, SiO2 had a negative effect. The coefficient of thermal expansion of glass showed an apparent linear relation to the contents of these three raw materials, from which an estimation model was built, to calculate the coefficient of thermal expansion of sealing glass. Relative errors of the calculating results to testing results were no more than 2%, which suggested that the estimation model was reasonable. This study provides a good theory reference for the practical utilizing of this sealing material, through which a proper glass composition for good sealing could be easily found.