Rational doping and compositional control remain significant challenges in designing luminescent metal halides to achieve highly efficient and tunable emission. Here, the air-stable lead-free Cs 2 InCl 5 •H 2 O crystal with a zero-dimensional structure was investigated as a pristine compound to design new luminescence materials. Sb 3+ -doping in Cs 2 InCl 5 •H 2 O:Sb 3+ enabled broadband yellow emission with a photoluminescence quantum yield up to 95.5%. The emission colors can be expanded into the orange-red region by halogen compositional substitution for Cs 2 InX 5 •H 2 O:Sb 3+ (X = Cl/Br/I). The optical characterizations along with the theoretical calculations demonstrate that the characteristic singlet and triplet self-trapped exciton emissions of ns 2metal-halide centers account for the tunable luminescence. Moreover, the admirable stability against air and heat pave way for its further applications in white light-emitting diodes and high-resolution fluorescent signs in anticounterfeiting technology. Our achievement in the case of Sb 3+ -doped Cs 2 InCl 5 •H 2 O represents a successful strategy for developing stable lead-free metal halides with highly efficient emission for versatile optical applications.

With the development of laser technology and related scientific fields, understanding of the structure-property relationships in nonlinear optical (NLO) crystals is becoming more and more important. In this article, first-principles studies based on density functional theory, and their applications to elucidate the microscopic origins of the linear and NLO properties in NLO crystals, are reviewed. The ab initio approaches have the ability to accurately predict the optical properties in NLO crystals, and the developed analysis tools are vital to investigating their intrinsic mechanism. This microscopic understanding has further guided molecular engineering design for NLO crystals with novel structures and properties. It is anticipated that first-principle material approaches will greatly improve the search efficiency and greatly help experiments to save resources in the exploration of new NLO crystals with good performance.

Solid solution is a potential way to optimize thermoelectric performance for its low thermal conductivity compared to those of the constituent compounds because of the phonon scattering from disordered atoms. Tin(II) sulfide (SnS) shows analogous band structure and electrical properties with tin selenide (SnSe), which was the motivation for investigating the thermoelectric performance of SnS and SnS-SnSe solid solution system. SnS compound and SnS 1Àx Se x (0 < x < 1) solid solution were fabricated using the melting method and they exhibited anisotropic thermoelectric performance along the parallel and perpendicular to the pressing directions. For the SnS compound, the maximum zT k value is 0.19 at 823 K along the parallel to pressing direction, which is higher than that along the perpendicular to the pressing direction (zT t ¼ 0.16). The zT values of SnS 0.5 Se 0.5 and SnS 0.2 Se 0.8 were higher than those of the SnS compound and a maximum zT value of 0.82 was obtained for SnS 0.2 Se 0.8 at 823 K, which is more than four times higher than that of SnS.

Finding new low-dimensional metal halides with broad-band emission is attracting interest in single-component phosphor for white light-emitting diodes (WLEDs). The full-spectrum white light still remains a challenge as found in the two-dimensional hybrid material (C6H18N2O2)­PbBr4 exhibiting the intrinsic free exciton (FE) and broad-band self-trap exciton (STE) emission upon 365 nm ultraviolet excitation, and a combined strategy has been proposed through doping the Mn2+ ions enabling a superposition of multiple emission centers toward the ultra-broad-band warm white light. The occupation of Mn2+ in (C6H18N2O2)­PbBr4 has been discussed, and optical investigations verify that the warm white-light emission of Mn2+-doped (C6H18N2O2)­PbBr4 originates from the coupling effects of the FE, STEs, and the 4T1–6A1 transition of the doped Mn2+. When the concentration of Mn2+ is 5%, the emission spectrum of the phosphor covers all visible-light areas with a full width at half maximum (FWHM) of about 230 nm. The high R a (84.9) and warm light CCT (3577 K) values of the as-fabricated WLED lamp demonstrate that (C6H18N2O2)­Pb1–x Mn x Br4 can be promising as single-component white-light phosphor in solid-state lighting. Our work could provide a new understanding and perspective about hybrid metal halides for designing superior phosphor toward single-component white emission.

CONSPECTUS:A hot topic in materials science is to search for nonlinear optical (NLO) crystals, which are indispensable in current laser technology, future optical information, and precision measurements. In the period of the 1980s and 1990s, the anionic group theory proposed by Prof. Chuangtian Chen has greatly promoted the inventions of BaB 2 O 4 (BBO), LiB 3 O 5 (LBO), and KBe 2 BO 3 F 2 (KBBF) which are widely applied in the ultraviolet (UV) spectral region today. From the beginning of this century, the rapid development of laser science and technology urgently demands new NLO crystals for wider application ranges. However, commercial NLO crystals in deep-UV and midinfrared (mid-IR) regions are scarce. The challenge arises from the stringent criteria at various wavelengths and inefficient exploration strategy. As such, more comprehensive and quantitative theoretical guidance is necessary to improve and supplement the NLO structure−property understandings. Benefiting from high-performance computing resources, first-principles design and simulations came into being, which is more applicable to the understanding of mid-IR NLO mechanism and suitable for the efficient design of new NLO structures for current needs. In the past decade, a complete set of computational research programs based on first-principles simulations have been developed, which have promoted the development of NLO crystals in the deep-UV and mid-IR regions, and guided the subsequent and further experimental explorations. Based on our developed first-principles materials design system, the discoveries of NLO materials have ranged from basic theoretical design to rapid-prototyping and final experimental synthesis. In this Account, we will concisely summarize our ab initio guided and forward-looking studies on NLO crystals, which are our original contributions to this field and can be consulted by other material fields. First, we will review the development of NLO crystals and the important features of NLO materials. Second, we will summarize the important role of computer-aided design in advancing the NLO material field and our developed NLO material design system based on the first-principles simulations. Third, we will introduce the first-principles design for new deep-UV NLO crystals using two novel design proposals, i.e., interlayer cationic replacement and intralayer anionic substitution. Meanwhile, we will illustrate the hierarchical molecular engineering optimizations for mid-IR NLO crystals by illustrating an extended mid-IR NLO family pedigree, from which many promising mid-IR NLO systems were predicted theoretically and confirmed experimentally. Finally, we will give an outlook to explore new functional NLO crystals guided by our first-principles design and simulations. We believe that the computerassisted exploration for new functional NLO materials is useful for understanding structure−property relationships and can provide researchers with a new approach to cost-effective and data-driven materials design.

A new nonlinear optical (NLO) material, BiTeBO (BTBO), is successfully grown from high temperature solution method. BTBO crystallizes in a polar space group of P6 with a framework structure composed of [BiO] blocks, with TeO and BO interconnection. It is interesting that in the BTBO structure three types of NLO-active units, including stereochemically active lone pair cations (Bi cations), second-order Jahn-Teller distorted octahedra (TeO octahedra) and π-orbital planar groups (BO groups), simultaneously exist. The additive contribution from these three types of groups results in an extremely large second harmonic generation (SHG) response in BTBO (about 20 times that of KDP), exhibiting the largest SHG effect among the known borate NLO materials. The enhancement of the nonlinear optical property is elucidated by the first-principles analysis.

Second-harmonic generation (SHG) response and birefringence are two critically important properties of nonlinear optical (NLO) materials. However, the simultaneous optimization of these two key properties remains a major challenge because of their contrasting microstructure requirements. Herein, we report the first tetravalent rare-earth metal fluorinated sulfate, CeF2(SO4). Its structure features novel net-like layers constructed by highly distorted [CeO4F4] polyhedra, which are further interconnected by [SO4] tetrahedra to form a three-dimensional structure. CeF2(SO4) exhibits the strongest SHG effect (8 times that of KH2PO4) and the largest birefringence for sulfate-based NLO materials, the latter exceeding the birefringent limit for oxides. Theoretical calculations and crystal structure analysis reveal that the unusually large SHG response and giant birefringence can be attributed to the introduction of the highly polarizable fluorinated [CeO4F4] polyhedra as well as the favorable alignment of [CeO4F4] polyhedra and [SO4] tetrahedra. This research affords a new paradigm for the designed synthesis of high-performance NLO materials.

Organic–inorganic hybrid metal halides with zero-dimensional (0D) structure has emerged as a new class of light-emitting materials. Herein, a new lead-free compound (C9NH20)2MnBr4 has been discovered and a temperature-dependent phase transition has been identified for two phases (space group P21/c and C2/c) in which individual [MnBr4]2– anions connect with organic cations, (C9NH20 +) (1-buty-1-methylpyrrolidinium+), forming periodic structure with 0D blocks. A green emission band, peaking at 528 nm with a high photoluminescence quantum efficiency (PLQE) of 81.08%, has been observed at room temperature, which is originated from the 4T1(G) to 6A1 transition of tetrahedrally coordinated Mn2+ ions, as also elaborated by density functional theory calculation. Accordingly, a fast, switchable, and highly selective fluorescent sensor platform for different organic solvents based on the luminescence of (C9NH20)2MnBr4 has been developed. We believe that the hybrid metal halides with high PLQE and the exploration of these as a fluorescence sensor will expand the applications scope of bulk 0D materials for future development.