Rational Design of Novel Promising Infrared Nonlinear Optical Materials: Structural Chemistry and Balanced Performances

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Second-order nonlinear optical (NLO) materials are currently a hot topic in modern solid-state chemistry and optics because they can produce coherent light by frequency conversion. Noncentrosymmetric (NCS) structure is not only the prerequisite for NLO materials but also a challengeable issue because materials tend to be centrosymmetric (CS) in terms of thermodynamical stability. Among NLO materials, an excellent infrared (IR) candidate should simultaneously meet several strict key conditions including a large NLO coefficient, high laser-induced damage threshold (LIDT), phase-matchable (PM) behavior, and so on. Achieving a balance between the large NLO effect and high LIDT is difficult, as they have contradictory requirements for chemical bonds. Considering the urgent need of the high-power IR laser market and the drawbacks of the available ones, exploring new highperformance IR NLO crystals is necessary while challenging. In this Account, we first briefly introduce the status and advancement of IR NLO crystals and emphasize the criteria of an excellent candidate. Then, we will introduce five simple methods developed by us to discover practical NLO candidates through understanding of the chemical composition−structure− NLO performance relationship. (1) A rarely investigated system with simple chemical compositions as new-type NLO crystals, namely, adducts containing S 8 molecules, are developed. Combining a chairlike S 8 unit with other units through van der Waals forces has successfully obtained several high-performance NLO adducts. (2) The main trend in exploring new NLO crystals is that the chemical composition is more and more diversified and the structure is more and more complex, and expensive and chemically active alkaline and alkaline earth metals are usually introduced as counter cations. In contrast, the research on systems with simple chemical compositions, simple structures, and low costs has been continuously ignored. The binary M 2 Q 3 (M = Ga, In; Q = S, Se) family with rich acentric modifications has been systematically investigated, and they all exhibit strong SHG effects and high LIDTs. (3) We first proposed the concept of inducing CS structures transformed to NCS ones by partial cation substitution to design novel NLO crystals. Considering the huge number of CS structures in the database compared to the number of NCS structures, it is an attractive method to apply CS structures as the parents to obtain potential NLO materials via partial-substitution-induced symmetry breaking. A series of chalcogenides with high NLO performances have been successfully obtained by us in this way. (4) We investigated the first NLO-active rare earth (RE) chalcophosphates and developed this family systematically, and they demonstrate wonderful comprehensive NLO properties. ( 5) We created a novel mixed-anion system for NLO applications, namely, chalcogenide borates. Usually, mixed-anion compounds can engender a synergistic effect to obtain desired IR NLO properties....

Centrosymmetric CaBaMF8 and Noncentrosymmetric Li2CaMF8 (M = Zr, Hf): Dimension Variation and Nonlinear Optical Activity Resulting from an Isovalent Cation Substitution-Oriented Design

“…Second-order nonlinear optical (NLO) materials have been identified as the forefront in the fields of laser science and technology on account of their applications in laser frequency conversion, modulation, etc. − The primary and central element of constructing NLO materials showing second-harmonic generation (SHG) response is the acquisition of the noncentrosymmetric (NCS) space group. − Nevertheless, the realization of the NCS structure is relatively difficult, and the number of compounds featuring the centrosymmetric (CS) structure is approximately five times that of NCS compounds. In the past few decades, scientists have studied and clarified the relationship between structures and properties, and proposed and validated several strategies for obtaining NCS compounds.…”

Anhydrous Aluminum Iodate: Strong Second Harmonic Generation Effect Contributed by Unbonded and Antibonding Orbitals

“…These include anion-based methods that aim to achieve a balance of properties in NLO crystals through mixed anion strategies. Representative classes of compounds resulting from this approach include but are not limited to chalcogenide borates, borate halides, and oxychalcogenides . Additionally, there are cation-based methods, which involve inducing symmetry breaking by cation partial chemical substitution to generate noncentrosymmetric structures …”

Polysubstitution Induced Centrosymmetric-to-Noncentrosymmetric Structural Transformation and Nonlinear-Optical Behavior: The Case of Na0.45Ag0.55Ga3Se5

“…As the key materials for all solid-state lasers, nonlinear-optical (NLO) materials can effectively expand the wavelength application range of lasers, and are widely used in laser medicine, environmental monitoring, laser communication, and material processing, etc. − However, due to the contradictory microstructure requirements of a strong second-harmonic-generation (SHG) effect and a high laser-induced damage threshold (LIDT), it is difficult to balance them especially for infrared (IR) NLO materials. − In fact, the IR NLO materials are relatively undeveloped and far from the market’s requirement. , Therefore, numerous explorations have been performed to discover potential materials. − Specifically, chalcogenides have received predominant attention in view of their large polarizability and wide IR transparent ranges. − …”