Bingbing Zhang

Finding the Next Deep-Ultraviolet Nonlinear Optical Material: NH4B4O6F

Nonlinear optical materials are essential for the development of solid-state lasers. KBe2BO3F2 (KBBF) is a unique nonlinear optical material for generation of deep-ultraviolet coherent light; however, its industrial application is limited. Here, we report a new material NH4B4O6F, which exhibits a wide deep-ultraviolet transparent range and suitable birefringence that enables frequency doubling below 200 nm. NH4B4O6F possesses large nonlinear coefficients about 2.5 times that of KBBF. In addition, it is easy to grow bulk crystals and does not contain toxic elements.

Fluorooxoborates: Beryllium-Free Deep-Ultraviolet Nonlinear Optical Materials without Layered Growth

Deep-ultraviolet nonlinear optical (DUV NLO) crystals are the key materials to extend the output range of solid-state lasers to below 200 nm. The only practical material KBe2 BO3 F2 suffers high toxicity through beryllium and strong layered growth. Herein, we propose a beryllium-free material design and synthesis strategy for DUV NLO materials. Introducing the (BO3 F)4- , (BO2 F2 )3- , and (BOF3 )2- groups in borates could break through the fixed 3D B-O network that would produce a larger birefringence without layering and simultaneously keep a short cutoff edge down to DUV. The theoretical and experimental studies on a series of fluorooxoborates confirm this strategy. Li2 B6 O9 F2 is identified as a DUV NLO material with a large second harmonic generation efficiency (0.9×KDP) and a large predicted birefringence (0.07) without layering. This study provides a feasible way to break down the DUV wall for NLO materials.

Hybrid Nanocarbon as a Catalyst for Direct Dehydrogenation of Propane: Formation of an Active and Selective Core–Shell sp2/sp3 Nanocomposite Structure

Hybrid nanocarbon, comprised of a diamond core and a graphitic shell with a variable sp(2)-/sp(3)-carbon ratio, is controllably obtained through sequential annealing treatment (550-1300 °C) of nanodiamond. The formation of sp(2) carbon increases with annealing temperature and the nanodiamond surface is reconstructed from amorphous into a well-ordered, onion-like carbon structure via an intermediate composite structure--a diamond core covered by a defective, curved graphene outer shell. Direct dehydrogenation of propane shows that the sp(2)-/sp(3)-nanocomposite exhibits superior catalytic performance to that of individual nanodiamond and graphitic nanocarbon. The optimum catalytic activity of the diamond/graphene composite depends on the maximum structural defectiveness and high chemical reactivity of the ketone groups. Ketone-type functional groups anchored on the defects/vacancies are active for propene formation; nevertheless, once the oxygen functional groups are desorbed, the defects/vacancies alone might be active sites responsible for the C-H bond activation of propane.

CsB4O6F: A Congruent‐Melting Deep‐Ultraviolet Nonlinear Optical Material by Combining Superior Functional Units

The discovery of new nonlinear optical (NLO) materials for coherent light generation in the deep-ultraviolet (DUV, wavelength below 200 nm) region is essential for the development of laser technologies. Herein, we report a new material CsB4 O6 F (CBF), which combines the superior structural properties of two well-known NLO materials, β-BaB2 O4 (BBO) and KBe2 BO3 F2 (KBBF). CBF exhibits excellent DUV optical properties including a short cutoff edge (155 nm), a large SHG response (≈1.9×KDP), and a suitable birefringence that enables frequency doubling down to 171.6 nm. Remarkably, CBF melts congruently and shows an improved growth habit. In addition, our rational design strategy will contribute to the discovery of DUV NLO materials.

Simulated pressure-induced blue-shift of phase-matching region and nonlinear optical mechanism for K3B6O10X (X = Cl, Br)

Birefringence plays a great role in phase matching of the nonlinear optical (NLO) crystals. Small birefringence restricts various crystals from achieving deep-ultraviolet laser output although they exhibit short UV cutoff edges and high second-harmonic generation (SHG) intensities. An access to achieve deeper coherent light output through external pressure on NLO crystal, K3B6O10Cl is proposed and demonstrated through computer experiment based on the first principles theory. The “hot spot” in structure that determine the SHG effects and birefringence were highlighted. The shortest achievable phase-matching wavelengths are predicted based on calculated refractive indices. It is found that the quasi-planar (B6O10)2− group is the dominant contributing unit to optical anisotropy. The pressure-induced increase of polarizability anisotropy of (B6O10)2− group can notably enlarge birefringence which extends the shortest achievable wavelength of K3B6O10Cl frequency conversion. The results show that pressure engineering may be a promising scheme to overcome the drawback of small birefringence of some NLO crystals.

High-responsivity, low-noise, room-temperature, self-mixing terahertz detector realized using floating antennas on a GaN-based field-effect transistor

Using only optical lithography, we have fabricated a GaN/AlGaN high-electron mobility transistor with distinctive source and drain antennas electrically isolated from the electron channel. Working at room temperature, it efficiently detects terahertz radiation via self-mixing, with a responsivity (3.6 kV/W) exceptionally high for a III-V device and with a noise (40 pW / ) just above the thermal limit. Performance improves at 77 K. While the device itself is micrometer-sized, our modeling indicates the asymmetric antennas induce a rather localized (<200 nm) region of strong self-mixing. Thus, a nanometer-scale active region is achieved by design and without recourse to electron-beam lithography

p–(p,π*) interaction mechanism revealing and accordingly designed new member in deep-ultraviolet NLO borates LinMn−1B2n−1O4n−2 (M = Cs/Rb, n = 3, 4, 6)

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, including Li3Cs2B5O10 (L3CBO), Li4Cs3B7O14 (L4CBO), and Li6Rb5B11O22 (L6RBO), which can be reduced to a general formula of LinMn−1B2n−1O4n−2 (M = Cs/Rb, n = 3, 4, 6). All of the three crystals exhibit a short UV cutoff edge (below 190 nm) and share a class of topologically similar BO groups interconnected by LiOn (n = 4, 5), Rb/CsOn (n = 8, 9, 10). The mechanism of NLO properties of this class of crystals was studied using band-resolved and SHG-density methods based on the first-principles theory. The results reveal that the “charge-transfer excitation” from the non-bonding 2p occupied states of O atoms to the π* and 2p unoccupied states of the BO3 substructure in BO groups is the key mechanism of NLO properties of this material family. Through systematic analyses on the relationship between crystal structure and NLO effects, a new crystal, Li4Rb3B7O14, was designed and subsequently synthesized through solid state reaction, which is isomorphic with Li4Cs3B7O14 and exhibits a short UV cutoff edge (below 190 nm) and a SHG response of 2/3 × KDP.

Room temperature GaN/AlGaN self-mixing terahertz detector enhanced by resonant antennas

This letter focuses on the fabrication and characterization of a terahertz detector integrated with a group of low pass filters and resonant antennas. The detector operates as a self-mixer on GaN/AlGaN high electron mobility transistor (HEMT). At room temperature, a strong dc photocurrent is produced with the aid of the antennas and filters. The responsivity of our HEMT device is estimated to be 53 mA/W and a noise equivalent power of 1 nW/Hz can be achieved at 300 K. In addition, the sensor properties of a similar HEMT detector without filter are tested as a comparison.

SrB5O7F3 Functionalized with [B5O9F3]6− Chromophores: Accelerating the Rational Design of Deep‐Ultraviolet Nonlinear Optical Materials

Fluorooxoborates, benefiting from the large optical band gap, high anisotropy, and ever-greater possibility to form non-centrosymmetric structures activated by the large polarization of [BOx F4-x ](x+1)- building blocks, have been considered as the new fertile fields for searching the ultraviolet (UV) and deep-UV nonlinear optical (NLO) materials. Herein, we report the first asymmetric alkaline-earth metal fluorooxoborate SrB5 O7 F3 , which is rationally designed by taking the classic Sr2 Be2 B2 O7 (SBBO) as a maternal structure. Its [B5 O9 F3 ]6- fundamental building block with near-planar configuration composed by two edge-sharing [B3 O6 F2 ]5- rings in SrB5 O7 F3 has not been reported in any other borates. Solid state 19 F and 11 B magic-angle spinning NMR spectroscopy verifies the presence of covalent B-F bonds in SrB5 O7 F3 . Property characterizations reveal that SrB5 O7 F3 possesses the optical properties required for deep-UV NLO applications, which make SrB5 O7 F3 a promising crystal that could produce deep-UV coherent light by the direct SHG process.

Luminescence and electronic properties of Ba2MgSi2O7:Eu2+: a combined experimental and hybrid density functional theory study

Photoluminescence properties of Ba2MgSi2O7:Eu2+ synthesized by a solid-state reaction method are first investigated in the vacuum ultraviolet (VUV) to visible (vis) excitation energy range. The band gap of the host is found to be around 7.44 eV. The incorporation of Eu2+ leads to bright green luminescence with weak thermal quenching above room temperature. Cathodoluminescence (CL) properties under low-voltage excitations are then studied, and the results suggest a potential application of the compound in field emission displays (FEDs). Electronic properties of the compound are finally calculated by a hybrid density functional theory (DFT) method, and are discussed in association with observed luminescence properties.