InCl3-Assisted Surface Defects Restoring to Enhance Lead-Free Cs2ZrCl6 Nanocrystals for X-Ray Imaging and Blue LED Applications.

As one type of recent emerging lead-free perovskites, Cs2ZrCl6 nanocrystals are widely concerned, benefiting from the eminent designability, high X-ray cutoff efficiency, and favorable stability. Improving the luminescence performance of Cs2ZrCl6 nanocrystals has great importance to cater for practical applications. In view of the surface defects frequently formed by the liquid phase method, the particle morphology and surface quality of this material are expected to be regulated if certain intervention is made in the synthesis process. In the work, differing from normal cell lattice modulation based on the ion doping, the grain size and surface morphology of Cs2ZrCl6 nanocrystals are optimized via adding a certain amount of InCl3 to the synthetic solution. The surface defects are restored to inhibit the defect-induced non-radiative transition, resulting in the improvement of the luminescence properties. Moreover, a flexible Cs2ZrCl6@polydimethylsiloxane film with excellent heat, water, and bending resistance and a light-emitting diode (LED) device are fabricated, exhibiting excellent application potential for X-ray imaging and blue LED.

Birefringence Regulation by Clarifying the Relationship Between Stereochemically Active Lone Pairs and Optical Anisotropy in Tin-based Ternary Halides.

It is important to establish and clarify the relationship between stereochemically active lone pairs and birefringence, since it is one of the significantly effective routes to explore birefringent crystals by introducing Sn-centered polyhedra with stereochemically active lone pairs. Herein, four tin(II)-based ternary halides A3 SnCl5 and ASn2 Cl5 (A=NH4 and Rb) have been synthesized successfully. The experimental birefringence of Rb3 SnCl5 and RbSn2 Cl5 is larger than or equal to 0.046 and 0.123@546 nm, respectively. Through investigating the alkali or alkaline-earth metal tin(II)-based ternary halides, the structure-performance relationship has been concluded between stereochemically active lone pairs and optical anisotropy. It is beneficial to the analysis and prediction of birefringence in tin-based halides and provides a guide for exploring tin(II)-based optoelectronic functional materials.

Enhancement of Birefringence in Borophosphate Pushing Phase-Matching into the Short-Wavelength Region.

Borophosphates are very known for the short ultraviolet (UV) cutoff edge and have become the promising UV and deep-UV functional crystals candidates; however, tetrahedral [PO4] and [BO4] groups own weak anisotropy of polarizability and are not conducive to large birefringence, which hinders their application in the short-wavelength region. Improving their birefringence without compromising the band gap is the main research objective. By introducing the excellent birefringent functional groups, such as [B2O5], [BO2]∞ chain, [B2Ox(OH)5-x], and so forth into borophosphates, seven borophosphates with improved birefringence were successfully synthesized (Δn > 0.05@532 nm). Remarkably, among them, the centimeter-sized crystal of Rb3B8PO16 with a short deep-UV cutoff edge (175 nm) and large birefringence (Δn(exp.) ∼ 0.072@589.3 nm) exhibits the shortest phase-matching wavelength (222 nm), which makes Rb3B8PO16 a promising UV NLO crystal, while KB6PO10(OH)4 with deep-UV cutoff edge features the largest birefringence (Δn(exp.) ∼ 0.103@546 nm) in the reported borophosphate system, making KB6PO10(OH)4 a promising deep-UV birefringent crystal. This study not only provides feasible strategies for increasing the birefringence of borophosphates but also pushes phase-matching into the short-wavelength region.

Hierarchical Modulation of Optical Anisotropy Driven by Metal Cation Polyhedra in Fluorooxoborates MII B4 O6 F2 (MII =Be, Mg, Pb, Zn, Cd).

The enhancement mechanism of birefringence is very important to modulate optical anisotropy and materials design. Herein, the different cations extending from alkaline-earth to alkaline-earth, d10 electron configuration, and 6s2 lone pair cations are highlighted to explore the influence on the birefringence. A flexible fluorooxoborate framework from AEB4 O6 F2 (AE=Ca, Sr) is adopted for UV/deep-UV birefringent structures, namely, MII B4 O6 F2 (MII =Be, Mg, Pb, Zn, Cd). The maximal enhancement on birefringence can reach 46.6 % with the cation substitution from Ca, Sr to Be, Mg (route-I), Pb (route-II), and Zn, Cd (route-III). The influence of the cation size, the stereochemically active lone pair, and the binding capability of metal cation polyhedra is investigated for the hierarchical improvement on birefringence. Significantly, the BeB4 O6 F2 structure features the shortest UV cutoff edge 146 nm among the available anhydrous beryllium borates with birefringence over 0.1 at 1064 nm, and the PbB4 O6 F2 structure has the shortest UV cutoff edge 194 nm within the reported anhydrous lead borates that hold birefringence larger than 0.1 at 1064 nm. This work sheds light on how metal cation polyhedra modulate birefringence, which suggests a credible design strategy to obtain desirable birefringent structures by cation control.

Daylight-White-Emitting and Abnormal Thermal Antiquenching Phosphors Based on a Layered Host SrIn2(P2O7)2.

Single-phase white-emission phosphors possess a judicious usage potential in phosphor-converted white-light-emitting diodes (WLEDs). Recently, numerous efforts have been made toward the development of new patterns of white-emitting phosphors that achieve excellent quantum yield, superior thermal stability, and applaudable cost effectiveness of WLEDs. Finding suitable single-component white phosphor hosts to provide an ideal local environment for activators remains urgent. Inspired by the original discovery of the promising host MgIn2(P2O7)2 (MIP) and its structural dependence on alkali-metal cations, we synthesized a brand-new phosphor host, SrIn2(P2O7)2 (SIP), via the traditional solid-state reaction. Its crystal structure was determined using an ab initio analysis and the Rietveld method. It belongs to a monoclinic unit cell with the space group C2/c. Besides, SIP exhibits a special layered three-dimensional framework in which the monolayer [SrO10]∞ was surrounded by a bilayer [In2P4O14]∞ made of the InO6 octahedra and P2O7 groups. A series of pure SIP:Tm3+,Dy3+ phosphors with tunable blue-white-yellow emission were prepared by adjusting the dopant concentration and utilizing the Tm3+-Dy3+ energy transfer. The daylight-white-emitting phosphor SIP:0.01Tm3+,0.04Dy3+ (the correlated color temperature is 4448 K) exhibits an abnormal thermal antiquenching property, and the emission intensity of 423 K reaches 103.7% of the initial value at 300 K. On the basis of the temperature-dependent lattice evolution and microenvironment analysis, the reduction of ß and lattice distortion can lead to lower asymmetry of the activators and benefit the compensation of trapped-electron thermal activation. In this work, an integration study was carried out on the crystal structure of the new matrix, the occupation of the luminescent center, the interaction of different activators in the host, and the distortion degree of the local structure for the activators, which is of great practical sense for producing a novel single-matrix white phosphor possessing superior thermal endurance for UV-light-stimulated WLEDs.

Li4 MgGe2 S7 : The First Alkali and Alkaline-Earth Diamond-Like Infrared Nonlinear Optical Material with Exceptional Large Band Gap.

Large band gap and strong nonlinear optical (NLO) effect are two valuable but contradictory parameters, which are difficult to balance in one infrared (IR) NLO material. Herein, the first alkali and alkaline-earth metal diamond-like (DL) IR NLO material Li4 MgGe2 S7 , presenting a honeycomb-like 3D framework constructed by 6-membered LiS4 rings and GeMgS6 zigzag chains, was rationally designed and synthesized. The introduction of rigid alkali metal and alkaline-earth metal LiS4 and MgS4 tetrahedra effectively broadens the band gap of DL compound to 4.12 eV (the largest one in the reported quaternary metal chalcogenides), generating a high laser damage threshold of 7 × AgGaS2 at 1064 nm. Furthermore, Li4 MgGe2 S7 displays a suitable SHG response (0.7 × AgGaS2 ) with a type I phase-matching behavior. The results indicate that Li4 MgGe2 S7 is a promising IR NLO material for the high-power laser application and it provides an insight into the design of new DL compound with outstanding IR NLO performances.

Al8(BO3)4(B2O5)F8: A F-Containing Aluminum Borate Featuring Two Types of Isolated B-O Groups.

Al8(BO3)4(B2O5)F8, as a new aluminum borate fluoride, has been synthesized by the high-temperature reaction with the closed system for the first time. With respect to its structure, the isolated BO3 and B2O5 groups reside in the center and edge of tunnels constructed by the AlO4F2 polyhedra. The AlO4F2 polyhedra play the vital role on the formation of isolated B-O groups. According to our investigation, Al8(BO3)4(B2O5)F8 is the first case, which features two types of independently isolated B-O groups in the aluminum borate fluorides. Its cutoff edge is up to deep ultraviolet (DUV) range. What is more, the energy dispersive spectroscopy (EDS), infrared (IR) spectrum, and the first-principles calculations of Al8(BO3)4(B2O5)F8 have been performed.

Design and Synthesis of a Series of Novel Mixed Borate and Carbonate Halides.

Combining different functional units together has been regarded as the most ideal strategy to design and synthesize new inorganic materials. Based on numerous experiments, it was possible to assemble three kinds of anion groups together and find a series of novel mixed borate and carbonate halides, Rb9 [B4 O5 (OH)4 ]3 (CO3 )X⋅7 H2 O (X=Cl, Br, and I) and K9 [B4 O5 (OH)4 ]3 (CO3 )X⋅7 H2 O (X=OH and I). Based on the structural template of these compounds, we also obtained the NaRb6 [B4 O5 (OH)4 ]3 X (X=OH, I) crystals through replacement of the CO3 group with the NaO6 octahedron, which results in the crystal structural changes from P6‾ 2c to R32. In addition, it has been confirmed that the replacement of the CO3 group by the alkali cation has an influence on the band gaps, according to the experimental results and theoretical calculations. Meanwhile, millimeter-scale crystals of Rb9 [B4 O5 (OH)4 ]3 (CO3 )I⋅7 H2 O, K9 [B4 O5 (OH)4 ]3 (CO3 )I⋅7 H2 O, K9 [B4 O5 (OH)4 ]3 (CO3 )OH⋅7 H2 O and NaRb6 [B4 O5 (OH)4 ]3 OH were also obtained after adjusting their growing conditions.

Correction: Wide band gap thiophosphates ASrPS4 (A = Li, Na, K, Rb, Cs): cation size effect induced successive structural transformation.

Correction for 'Wide band gap thiophosphates ASrPS4 (A = Li, Na, K, Rb, Cs): cation size effect induced successive structural transformation' by Yi Huang et al., Dalton Trans., 2022, 51, 15067-15073, https://doi.org/10.1039/D2DT02321K.

Wide band gap thiophosphates ASrPS4 (A = Li, Na, K, Rb, Cs): cation size effect induced successive structural transformation.

Metal thiophosphates have aroused much research interest due to their structural chemistry and possible applications as infrared functional materials. In this study, five quaternary Sr-based alkali metal thiophosphates ASrPS4 (A = Li, Na, K, Rb, Cs) were obtained. Their structural comparison shows that their symmetry undergoes transformation from tetragonal (I41/acd) to monoclinic (P21/c) to orthorhombic (Pnma) system, which is induced by the cation size effects and coordination features of different alkali metal cations. The experimental and theoretical results demonstrate that the band gaps of all title compounds are large, namely 3.6-3.9 eV (experimental results) and 3.78-4.12 eV (HSE06). Theoretical analyses indicate that the [PS4] group could be regarded as a good unit for designing wide band gap compounds, and the birefringence of NaSrPS4 is 0.08 at the fundemental 1064 nm wavelength, which shows that it may be a potential infrared birefringent material.

Ba2B5O8(OH)2(NO3)·3H2O: the design of an alkaline earth metal borate-nitrate optimized from a hydroxylic borate.

The first alkaline earth metal borate-nitrate, namely Ba2B5O8(OH)2(NO3)·3H2O (BBNOH), has been synthesized by the hydrothermal method. BBNOH crystallizes in the space group of P21/c and shows two-dimensional (2D) 2∞[B5O8(OH)2]3- borate anion layers, and the hydrated barium cations and the [NO3]- anions are located between the layers. The process of optimizing the structure of Ba2B5O8(OH)2OH to BBNOH has been discussed. The first principles calculation has been used to calculate the birefringence of Ba2B5O8(OH)2(NO3)·3H2O, and the value is 0.033@1064 nm, which is mainly originated from the borate anions and the π conjugated [NO3]- anions.

Distinctive modulation of optical anisotropy by halogens in α/ß-Cd-P-X (X = Cl, Br, and I).

Birefringent materials are widely applied as photoelectric functional field devices to modulate the polarization of lasers. The introduction of a halogen into the structure of crystals could balance the relationship between the band gap Eg and nonlinear optical (NLO) coefficient owing to their outstanding electronegativity and control the optical anisotropy. In this work, the optical properties of phosphohalides α/ß-Cd2P3X (X = Cl, Br, I) were studied. It was found that the birefringences of α/ß-Cd2P3Cl (0.23/0.24 @ 1064 nm) are unexpectedly 8 times larger than those of α/ß-Cd2P3I (0.04/0.03 @ 1064 nm). To find the optical property origins and explore the contributions of microscopic groups to the optical anisotropy and NLO responses in Cd-P-X (X = Cl, Br, I), the first-principles, real-space atom-cutting, and polarizability anisotropy analysis methods were used. This reveals that the electron distribution is susceptible to halogen electronegativity. Halogen atoms can modulate the polarization anisotropy of the active polyhedron and influence the birefringence significantly, owing to the synergistic effect of the anion size and strong covalent interactions between halogens and metal cations. This work clarifies the optical anisotropy origin mechanism and provides a general strategy for finding promising birefringent crystals in phosphohalide systems.

SrTi(IO3)6·2H2O and SrSn(IO3)6: distinct arrangements of lone pair electrons leading to large birefringences.

Three new iodates SrTi(IO3)6·2H2O, (H3O)2Ti(IO3)6, and SrSn(IO3)6 have been synthesized via a facile hydrothermal method. The three compounds have zero-dimensional crystal structures composed of one [MO6]8- (M = Ti, Sn) octahedron connected with six [IO3]- trigonal pyramids. However, the particular coordination of Sr2+ cations results in distinct arrangements of lone pair electrons in an [IO3]- trigonal pyramid, which leads to large birefringences. More importantly, this work enriches the species crystal chemistry for [M(IO3)6]2- (M = Ti, Sn) clusters-containing iodates.

Large optical polarizability causing positive effects on the birefringence of planar-triangular BO3 groups in ternary borates.

The structure-property relationship of photoelectric functional materials has been recognized as a hot topic. The study of the inner link between the band gaps and birefringence of optical materials is extremely crucial for the design and creation of novel optical devices, but still remains rather unexplored. In this work, taking a series of borates with only planar-triangular BO3 groups, α-/ß-TM3(BO3)2 (TM = Zn, Cd), Cd2B2O5, and M3(BO3)2 (M = Hg, Mg, Ca, Sr) as the research subject, the comprehensive relationship between their electronic structures and linear optical properties has been systematically investigated. Through combining experimental measurements and theoretical calculations, the effect of optical polarizability on the birefringence of these borates was clarified. Based on the present discussion, the relationship between the O (2p) bandwidth of the highest valence band and the HSE06 band gaps is opposite. Meanwhile, a method involving the determination of so-called optical permittivity Δε to evaluate the magnitude of birefringence Δn is found to be feasible. A large Δε makes a positive contribution to Δn. In addition, the experimentally measured band gaps and IR vibrations are in good agreement with theoretical results for the compounds α-Cd3(BO3)2 and Cd2B2O5.