Deep-ultraviolet (DUV, wavelength λ < 200 nm) nonlinear optical (NLO) crystal is the core component of frequency conversion to generate DUV laser, which plays an important role in cutting-edge laser ...technology and fundamental science. Significant progress has been made in both experimental exploration and theoretical design in the field of DUV NLO crystals over the past three decades. In-depth insight into "structure-property correlations", in particular, allows for rigorous and precise identification of DUV NLO crystals. In this article, we reviewed the current experimental and theoretical research progress while elucidating the core concepts and stringent criteria of qualified DUV phase-matched second-harmonic generation crystals. We also discussed the development of the DUV NLO "structure-property correlations" from first principles and how it has sparked interest in related materials, as well as future directions for obtaining potential DUV NLO crystals.
Through the combination of Bi3+ and a large negative charge ion (BO3)3–, two novel Bi-based borate photocatalysts Bi4B2O9 and Bi2O2BO2(OH) with layered structure have been successfully developed. For ...the first time, the borates were investigated as photocatalysts. They were synthesized by solid-state reaction and hydrothermal method, respectively, and further characterized by XRD, SEM, TEM, HRTEM, and DRS. Bi4B2O9 and Bi2O2BO2(OH) possess direct and indirect transition optical band gaps of 3.02 and 2.85 eV, respectively. Density functional calculations revealed that the valence band (VB) and conduction band (CB) of both borates were composed of hybridized states of the O 2p and Bi 6p or 6s orbitals, and a large dispersion was observed in the energy band of Bi2O2BO2(OH). The photodecomposition experiments demonstrated that Bi4B2O9 and Bi2O2BO2(OH) can be used as effective photocatalysts under simulated solar irradiation, and Bi2O2BO2(OH) exhibits the high photocatalytic activity, which is 2.5 and 3.2 times compared with that of P25 and Bi2O2CO3, respectively. Moreover, the photocurrent conversion further confirmed that Bi4B2O9 and Bi2O2BO2(OH) were potential photofunctional materials. The layered structure with (Bi2O2)2+ layer, hybridized and dispersion energy band, and large negative charge of (BO3)3– ion should be responsible for the high photocatalytic activity of Bi2O2BO2(OH).
Hydrostatic pressure, as an alternative of chemical pressure to tune the crystal structure and physical properties, is a significant technique for novel function material design and fundamental ...research. In this article, we report the phase stability and visible light response of the organolead bromide perovskite, CH3NH3PbBr3 (MAPbBr3), under hydrostatic pressure up to 34 GPa at room temperature. Two phase transformations below 2 GPa (from Pm3̅m to Im3̅, then to Pnma) and a reversible amorphization starting from about 2 GPa were observed, which could be attributed to the tilting of PbBr6 octahedra and destroying of long-range ordering of MA cations, respectively. The visible light response of MAPbBr3 to pressure was studied by in situ photoluminescence, electric resistance, photocurrent measurements and first-principle simulations. The anomalous band gap evolution during compression with red-shift followed by blue-shift is explained by the competition between compression effect and pressure-induced amorphization. Along with the amorphization process accomplished around 25 GPa, the resistance increased by 5 orders of magnitude while the system still maintains its semiconductor characteristics and considerable response to the visible light irradiation. Our results not only show that hydrostatic pressure may provide an applicable tool for the organohalide perovskites based photovoltaic device functioning as switcher or controller, but also shed light on the exploration of more amorphous organometal composites as potential light absorber.
Combining high-throughput screening and machine learning models is a rapidly developed direction for the exploration of novel optoelectronic functional materials. Here, we employ random forests ...regression (RFR) model to investigate the second harmonic generation (SHG) coefficients of nonlinear optical crystals with distinct diamond-like (DL) structures. 61 DL structures in Inorganic Crystallographic Structure Database (ICSD) are selected, and four distinctive descriptors, including band gap, electronegativity, group volume and bond flexibility, are used to model and predict second-order nonlinearity. It is demonstrated that the RFR model has reached the first-principles calculation accuracy, and gives validated predictions for a variety of representative DL crystals. Additionally, this model shows promising applications to explore new crystal materials of quaternary DL system with superior mid-IR NLO performances. Two new potential NLO crystals, Li
CuPS
with ultrawide bandgap and Cu
CdSnTe
with giant SHG response, are identified by this model.
The fundamental catalytic limitations for the photoreduction of CO2 still remain: low efficiency, poor charge transport and short lifetime of catalysts. To address the critical challenges, an ...efficient strategy based on spatial location engineering of phosphate (PO4) and oxygen-vacancy (Vo) confined in Bi2WO6 (BWO) atomic layers is employed to establish and explore an intimate functional link between the electronic structures and activities of Vo-PO4-BWO layers. Both theoretical and experimental results reveal, the Vo-PO4-BWO layers not only narrow the band gap from the UV to visible-light region but also reduce the resistance. The time-resolved photoluminescence decay spectra exhibit the increasing carrier lifetime for Vo-PO4-BWO layers, indicating the improved charge separation and transfer efficiency. As expected, the Vo-PO4-BWO layers with the simultaneously efficient light absorption and charge transport properties achieve much higher methanol formation rate of 157 μmol g-1 h-1, over 2 and 262 times larger than that of BWO atomic layers and bulk BWO. This work may reveal that the light absorption and spatial charge transport over atomic layers could benefit CO2 conversion and shed light on the design principles of efficient photocatalysts towards solar conversion applications.
Simultaneously efficient light absorption and charge transport in phosphate and oxygen-vacancy confined in bismuth tungstate atomic layers have been achieved for excellent visible-light-driven CO2 reduction. Display omitted
•Phosphate and oxygen-vacancy confined in BWO atomic layers were achieved•Vo-PO4-BWO atomic layers exhibit efficient light absorption and charge transport•Vo-PO4-BWO layers present highest methanol formation by CO2 photoreduction•Mechanism of CO2 photoreduction over Vo-PO4-BWO atomic layers is proposed
The presence of extremely large negative linear compressibilities (NLC) in crystalline silver oxalate was discovered in a recent work by using first principles solid-state calculations. Although the ...minimum value of the NLC was found for a negative applied hydrostatic pressure, in this work the presence of NLC in this material for positive applied pressures is verified experimentally by means of high-pressure X-ray diffraction experiments performed at room temperature in the Beijing synchrotron radiation facility. The results of this study demonstrate with certainty that the compressibility of silver oxalate along 010 crystallographic direction is negative for applied pressures in the range from 0.0 to 0.85 GPa. Since the measured compressibility decreases largely as the pressure decreases, large negative values of the compressibility are expected for negative applied pressures in agreement with the results found using first principles methods. Furthermore, the analysis of the variation of the lattice parameters of the crystal structure of silver oxalate under pressure in the principal axes reference system revealed that this material also exhibits the largest negative area compressibility phenomenon found so far at zero pressure, the values of the compressibilities along two of the principal axes being − 16.7 and − 20.0
TPa
-
1
. The negative compressibility phenomenon in silver oxalate can be rationalized in terms of a “chains of rotating parallelograms” structural model.
The rapid development of deep‐UV (DUV) all‐solid‐state laser sources greatly depends on the good performance of the nonlinear optical (NLO) crystals used for harmonic generation. In this work, the ...potential prospects for NLO borate crystals are investigated from the point of view of their structure–property relationships. The microscopic structural units, energy bandgaps, linear and nonlinear optical properties of numerous borate compounds with diverse structural features are compared and summarized. The results reveal that KBe2BO3F2 almost achieves the theoretical limits of DUV NLO borates. It would be a great challenge to discover other borates which have comparable NLO capability, especially for coherent light production below the wavelength of 190 nm by direct second harmonic generation.
The access to deep‐UV (DUV) sources depends greatly on the performance of nonlinear optical (NLO) crystals used in all‐solid‐state lasers. This paper discusses the structure‐induced properties of the declared promising DUV NLO borates since the development of KBe2BO3F2, and forecasts their prospects of application. The KBe2BO3F2 is so far the best DUV NLO borate, and has yet to be surpassed.
Abstract
Anomalous mechanical materials, with counterintuitive stress-strain responding behaviors, have emerged as novel type of functional materials with highly enhanced performances. Here we ...demonstrate that the materials with coexisting negative, zero and positive linear compressibilities can squeeze three-dimensional volume compressibility into one dimension, and provide a general and effective way to precisely stabilize the transmission processes under high pressure. We propose a “corrugated-graphite-like” structural model and discover lithium metaborate (LiBO
2
) to be the first material with such a mechanical behavior. The capability to keep the flux density stability under pressure in LiBO
2
is at least two orders higher than that in conventional materials. Our study opens a way to the design and search of ultrastable transmission materials under extreme conditions.
There has been strong and growing interest in the development of cost-effective and highly active oxygen evolution reaction (OER) electrocatalysts for alternative fuels utilization and conversion ...devices. We report herein that semimetallic Cu3P nanoarrays directly grown on 3D copper foam (CF) substrate can function as effective electrocatalysts for water oxidation. Specifically, the surface oxidation-activated Cu3P only required a relatively low overpotential of 412 mV to achieve a current density of 50 mA cm–2 and displayed a small Tafel slope of 63 mV dec–1 in 0.1 M KOH solution, on account of the collaborative effect of large roughness factor (RF) and semimetallic character. Following that, investigations into the mechanism revealed the formation of a unique active phase during the water oxidation process in which conductive Cu3P was the core covered with a thin copper oxide/hydroxide layer. Moreover, this Cu3P 3D electrode was also applied to the hydrogen evolution reaction (HER) and showed good catalytic performance and stability under the same basic conditions.
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