The development of new nonlinear optical (NLO) materials for deep-ultraviolet (DUV) applications is in great demand. However, the synthesis of an ideal DUV NLO crystal is a serious challenge. Herein, three new alkali-metal fluorooxoborates, AB O F (A=K, Rb, and Cs, and a mixed cation between two of them), were successfully synthesized by cation regulation. It is found that all reported compounds exhibit short UV absorption edges (<190 nm), and show second harmonic generation (SHG) responses ranging from 0.8 to 1.9 KH PO (KDP). Interestingly, by judicious selection of the A-site alkali-metal cations, the arrangement of NLO-active structural units is fine-tuned to an optimal configuration, which contributes to large SHG responses.

If a bucket is to hold more water, its shortest plank must be made longer. This guideline also applies to the exploration of ultraviolet (UV) and deep-UV (DUV) nonlinear optical (NLO) materials that are limited by multiple criteria. Phosphates are one kind of promising candidate for new NLO materials. Unfortunately, the small birefringence, as the shortest plank, severely restricts the phase-matching of second harmonic generation (SHG) in the UV/DUV region. In this work, fluorophosphates are rationally proposed as substitutes for phosphates to break down the limitation of birefringence and simultaneously enhance SHG response and retain wide UV transmittance. The (PO3F)2– and (PO2F2)− groups are confirmed as superior material genomes to achieve the discussed combination properties. Accordingly, (NH4)2PO3F was screened out by density functional theory calculation, and single crystals with centimeter size have been grown. It possesses a powder SHG efficiency of 1 × KH2PO4 (KDP) and is phase-matchable with output of SHG wavelength at 266 nm. To the best of our knowledge, it is the first time that fluorophosphates are identified and developed as new and ideal candidates to new UV/DUV NLO materials by combining theories and experiments.

N onlinear optical (NLO) crystals are of great importance in producing coherent ultraviolet−visible (UV−vis), deep-UV (DUV), or infrared (IR) light sources for civil and military applications by frequency-conversion technology. 1−23 Borates are widely applied as short-wave NLO materials because of their large bandgaps and high laser damage threshold that originate from strongly covalent B−O bonds in [BO 3 ] 3− and [BO 4 ] 5− anionic groups, such as β-BaB 2 O 4 , 1 LiB 3 O 5 , 2 KBe 2 BO 3 F 2 , 3 etc.; unfortunately, they cannot be used in the IR region because of absorption resulting from their B− O vibration modes which limits the infrared transmission. Meanwhile, chalcogenides, 6 owing to its wide optical transmission range and strong NLO response, are wildly researched for IR NLO materials. Recently, in view of the performance drawbacks (low laser damage threshold (LDT) and harmful two photon absorption) of commercial IR NLO materials, 24−26 it is urgent to explore new excellent IR NLO materials 27−33 with suitable balance between wide bandgap (E g ≥ 3.0 eV) and large second harmonic generation (SHG) effect (NLO coefficient d ij ≥ 0.5 × benchmark AgGaS 2 ). 34

Exploration on the compounds in the complex alkali metal borate system had resulted in the discovery of a class of deep-ultraviolet second-order nonlinear optical (NLO) materials LinMn−1B2n−1O4n−2 (M = Cs/Rb, n = 3, 4, 6).

The development of new nonlinear optical (NLO) materials for deep‐ultraviolet (DUV) applications is in great demand. However, the synthesis of an ideal DUV NLO crystal is a serious challenge. Herein, three new alkali‐metal fluorooxoborates, AB4O6F (A=K, Rb, and Cs, and a mixed cation between two of them), were successfully synthesized by cation regulation. It is found that all reported compounds exhibit short UV absorption edges (<190 nm), and show second harmonic generation (SHG) responses ranging from 0.8 to 1.9 KH2PO4 (KDP). Interestingly, by judicious selection of the A‐site alkali‐metal cations, the arrangement of NLO‐active structural units is fine‐tuned to an optimal configuration, which contributes to large SHG responses.

Borates are one of the most important classes of functional materials, and several hundreds of artificial borates have been synthesized. The substitution of oxygen by fluorine leads to manifold classes of borates. Fluorooxoborates (also known as fluoroborates), in which the F atoms covalently connect with the B atoms, show additional compositional and structural diversity compared to classic borates. Recently, owing to the large polarizability anisotropy, large HOMO-LUMO gaps, and high hyperpolarizability of the oxyfluoride BO F building blocks, fluorooxoborates have received unprecedented attention in the search for new ultraviolet (UV) and deep-UV (DUV) nonlinear optical (NLO) materials. Specifically, some compounds have excellent NLO properties that are comparable or superior to KBe BO F , which is the only usable crystal that generates coherent light below 200 nm through a direct second harmonic generation (SHG) process. This Minireview illustrates recent progress on the synthesis, crystal structures, structure-properties relationships and applications of fluorooxoborates. This paper concludes by highlighting the outstanding opportunities offered by NLO fluorooxoborate crystals as an innovative avenue for DUV all solid-state coherent light generation.

The exploration of infrared (IR) nonlinear optical (NLO) materials remains attractive because of the urgent requirements in the laser field. Meanwhile, the deepened cognition of structure-property relationships is necessary to help guide the exploration of IR NLO materials. So far, the family of antimony sulfides is an important system with a lot of attention, and a series of antimony sulfides are reported. However, it is urgent to reveal how different Sb-S units, like SbS, SbS, and more complex combinations, affect apparent properties. Here, taking ternary metal antimony sulfides as examples, the sources of some essential optical properties, such as second harmonic generation (SHG) and birefringence, are systematically analyzed through first-principles calculations, and the mechanisms of the performances with various magnitudes are also presented to clarify the structure-property relationships. The results indicate that the SbS unit among antimony sulfides is an advantageous NLO-active unit, which can balance the contradiction between the band gap and SHG response. Introduction of transition metals in the Sb-S anionic frameworks can tune the magnitude of birefringence. Besides, the substitution of a cation from a transition metal to an alkali metal can notably enlarge the band gap and maintain a large SHG response. These design strategies are beneficial to explore potential IR NLO materials with Sb-S units.

Three acentric type-I phase-matchable infrared nonlinear optical materials KSbP2S6, KBiP2S6, and K2BaP2S6, showing excellent balance between second harmonic generation coefficient, bandgap, and laser damage threshold, were synthesized via a high-temperature...