Ultraviolet Nonlinear Optical Materials Research Articles

High-power 266 nm laser generation with a NaSr3Be3B3O9F4 crystal.

We demonstrate a 266nm ultraviolet (UV) picosecond laser by fourth-harmonic generation of a Nd:YAG laser with a 5.4mm thick NaSr3Be3B3O9F4 (NSBBF) crystal. A maximum output power exceeding 1W at 266nm was obtained (the highest output power being 1.6W), corresponding to a conversion efficiency of 10.3%. The stability measurements on the NSBBF crystal with a fluctuation of 3.34% at 200mW within 1h indicate that it is a promising UV nonlinear optical material for practical applications. In addition, for the first time, to the best of our knowledge, we measured the effective nonlinear coefficient of NSBBF crystal at 266nm and compared it with that of β-BaB2O4 crystal.

Fluorooxoborates: Ushering in a New Era of Deep Ultraviolet Nonlinear Optical Materials.

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 BOx F4-x 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 KBe2 BO3 F2 , 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.

Tailoring nonlinear optical crystal borophosphate through the introduction of transition metal d orbitals for improving optical anisotropy and SHG response: a first-principles investigation

Motivated by the discovery of practical and economical nonlinear optical (NLO) materials with strong second harmonic generation (SHG), experimental and theoretical researches have been widely carried out. However, drawbacks in one or some respects, especially poor birefringence, preclude their use for NLO applications in optoelectronic technologies. In the present work, taking the case of nonlinear material borophosphate BPO4, a systematic calculation of the structure, electronic, linear and nonlinear optical properties of the BP1−xVxO4 systems (x = 0, 0.25, 0.5, 0.75, and 1) are presented to tailor its small birefringence and assess their ultraviolet NLO capabilities based on first-principles calculations. Particularly, birefringences of the four V-containing compounds are significantly enhanced to fulfill the phase matching conditions in the ultraviolet region. Meanwhile, their SHG responses are greatly improved, especially for BP0.5V0.5O4, with moderate optical anisotropy of refraction (about 0.08 in transparent regions) and strong second harmonic generation response (almost ten times as compared with BPO4). Besides, a detailed analysis of their electronic characters, the polarizability anisotropy and local dipole moments of asymmetry functional building [BO4]5−, [PO4]3−, and [VO4]3− units are elucidated to understand the high performance of BP1−xVxO4 systems. These candidates would extend the ultraviolet nonlinear optical materials. Furthermore, the strategy of introducing transition metal d orbitals could be a promising way to tailor electronic structures and optical anisotropy in other functional materials for advanced photonic devices.

Ba3Mg3(BO3)3F3 polymorphs with reversible phase transition and high performances as ultraviolet nonlinear optical materials

Nonlinear optical (NLO) materials are the vital components of future photoelectric technologies as they can broaden the tunable wavelength range supplied by common laser sources. However, the necessary prerequisites for a practical NLO material are rather strict. Accordingly, considerable efforts have been focused on finding potential NLO materials. Here we report two asymmetric beryllium-free borates Pna21- and Pbar 62m-Ba3Mg3(BO3)3F3 featuring NLO-favorable 2∞[Mg3O2F3(BO3)2] layered structures. The reversible phase transition among two polymorphs was demonstrated by multiple experimental tests. The optical measurements reveal that Pna21-Ba3Mg3(BO3)3F3 possesses the optical properties required for ultraviolet NLO applications. Remarkably, Pna21-Ba3Mg3(BO3)3F3 has a large laser damage threshold, a deep-ultraviolet cutoff edge, a favorable anisotropic thermal expansion as well as the capacity of insolubility in water. These optical properties can be comparable or superior to that of commercial NLO material β-BaB2O4, which make Pna21-Ba3Mg3(BO3)3F3 a promising ultraviolet NLO material.

Expanding Frontiers of Ultraviolet Nonlinear Optical Materials with Fluorophosphates

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 ou...

Ba4B8TeO19: A UV Nonlinear Optical Material

We report a new noncentrosymmetric barium tellurium borate, Ba4B8TeO19 that has potential ultraviolet (UV) nonlinear optical (NLO) applications. Ba4B8TeO19 was synthesized by a flux method and crystallizes in the noncentrosymmetric space group Cc. The material exhibits a framework structure of [B8O17]∞ double layers connected to distorted TeO6 octahedra. Second harmonic generation (SHG) measurements at 1064 and 532 nm on polycrystalline Ba4B8TeO19 indicate that the title compound is phase-matchable (type I) with a moderate SHG response (1 × KH2PO4 at 1064 nm and 0.2 × β-BaB2O4 at 532 nm). In addition, a short absorption edge (210 nm) was measured. Using density functional theory calculations, we show that the SHG response originates from contributions from O 2p and Te 5s states at the valence and conduction band edges. Finally, by computing the linear optical properties, we find that this compound displays a moderate birefringence of 0.055 at 1064 nm and 0.059 at 532 nm, necessary conditions for phase-matching in UV NLO materials.

Pb2BO3Br: a novel nonlinear optical lead borate bromine with a KBBF-type structure exhibiting strong nonlinear optical response

Introducing a halogen bromine atom into a PbO–B2O3system generates a novel nonlinear optical material Pb2BO3Br.

Chemical Cosubstitution-Oriented Design of Rare-Earth Borates as Potential Ultraviolet Nonlinear Optical Materials.

A chemical cosubstitution strategy was implemented to design potential ultraviolet (UV) and deep-UV nonlinear optical (NLO) materials. Taking the classic β-BaB2O4 as a maternal structure, by simultaneously replacing the Ba2+ and [B3O6]3- units with monovalant (K+), divalent (alkaline earth metal), trivalent (rare-earth metal, Bi3+) ions, and the [B5O10]5- clusters through two different practical routes, 12 new mixed-metal noncentrosymmetric borates K7MIIRE2(B5O10)3 (MII = Ca, Sr, Ba, K/RE0.5; RE = Y, Lu, Gd) as well as K7MIIBi2(B5O10)3 (MII = Pb, Sr) were successfully designed and synthesized as high-quality single crystals. The selected K7CaY2(B5O10)3, K7SrY2(B5O10)3, and K7BaY2(B5O10)3 compounds were subjected to experimental and theoretical characterizations. They all exhibit suitable second-harmonic generation (SHG) responses, as large as that of commercial KH2PO4 (KDP), and also exhibit short UV cutoff edges. These results confirm the feasibility of this chemical cosubstitution strategy to design NLO materials and that the threeselected crystals may have potential application as UV NLO materials.

Structurally stable borate as a UV nonlinear optical material

A new phase-matching borate K3Sr3Li2Al4B6O20F features double-layer structure similar to that of the outstanding ultraviolet nonlinear optical material Sr2Be2B2O7, and thus inherits its excellent linear and nonlinear optical properties in some degree. Furthermore, it overcomes the structurally dynamical instability problem existing in Sr2Be2B2O7. The first-principles calculations and anionic group theory are employed to explain these properties.

Facile Syntheses of Ba2[B4O7(OH)2] and Na[B5O7(OH)2](H2O) Borate Salts Exhibiting Nonlinear Optical Activity in the Ultraviolet.

Two novel noncentrosymmetric metal borates, Ba2[B4O7(OH)2] (1) and Na[B5O7(OH)2](H2O) (2), have been obtained by hydrothermal and surfactant-thermal means. Compound 1 consists of novel one-dimensional borate chains formed by B3O9 and B3O8 rings, assembled into a three-dimensional (3D) framework by Ba2+ cations. The structure of 2 exhibits double-helical chains constructed from B5O10 primary building units, which are interconnected via Na+ cations and H-bonding interactions to generate a 3D framework. Second-harmonic-generation (SHG) measurements show that 1 shows a phase-matching powder SHG response of ∼2.2 × KH2PO4 (KDP), while 2 exhibits a weak SHG response. The cutoff edges of 1 and 2 are ∼242 and ∼221 nm, respectively, which suggests that they are potential ultraviolet nonlinear optical (NLO) materials. Band structures and NLO properties have also been theoretically studied.

Low-temperature-flux syntheses of ultraviolet-transparent borophosphates Na4MB2P3O13 (M = Rb, Cs) exhibiting a second-harmonic generation response.

The first non-centrosymmetric mixed-alkali-metal borophosphates, Na4MB2P3O13 (M = Rb 1, Cs 2), were obtained using a low-temperature flux method. Single-crystal X-ray diffraction studies of 1 and 2 reveal that the two compounds are isostructural, both crystallizing in the orthorhombic space group Pna21; their structures consist of novel 1D borophosphate chains constructed from B2P3O14 fundamental building units, assembled into a 3D framework by alkali metal cations. Second-harmonic generation (SHG) measurements show that 1 and 2 are type-I phase-matchable, with SHG responses ca. 0.35 and 0.42 times that of KH2PO4, respectively. The cut-off edges of 1 and 2 are ca. 276 and 267 nm, respectively, which suggests that they are potential ultraviolet nonlinear optical materials. Density functional theory calculations were employed to shed light on the band structure and density of states as well as the electron density distribution.

Strong Nonlinear-Optical Response in the Pyrophosphate CsLiCdP2O7 with a Short Cutoff Edge.

A high efficiency of laser-light conversion and short cutoff edge is essential to an ultraviolet (UV) nonlinear-optical (NLO) material. Previous researches on phosphates were mainly centered on alkali-metal or alkali-earth-metal phosphate systems, resulting in relatively weak NLO responses. Through the introduction of transition-metal cadmium and alkali-metal cesium elements with large radii into the phosphate system, a new UV NLO pyrophosphate, CsLiCdP2O7, has been synthesized. It exhibits a high second-harmonic-generation (SHG) efficiency of 1.5KH2PO4 and is transparent down to 200 nm. This work provides a new path for the design of UV NLO materials with high SHG efficiencies and short cutoff edges by introducing a transition metal with a d10 electron configuration and an alkali metal with a large radius into phosphate systems.

ChemInform Abstract: Deep Ultraviolet Nonlinear Optical Materials

AbstractReview: 185 refs.

K3B3O4(OH)4·2H2O: A UV Nonlinear Optical Crystal with Isolated [B3O4(OH)4](3-) Anion Groups.

A potential ultraviolet (UV) nonlinear optical (NLO) material, K3B3O4(OH)4·2H2O, was successfully synthesized by hydrothermal methods. The compound crystallizes into the Cmc21 space group and exhibits isolated [B3O4(OH)4](3-) anion groups connected by O-H···O hydrogen bonds. The UV-vis diffuse reflectance spectrum shows that K3B3O4(OH)4·2H2O has a wide transparency range with an absorption edge below 190 nm. Powder second harmonic generation (SHG) measurements using 1064 nm radiation revealed a moderate efficiency, 0.8 × KDP. Additional particle size vs SHG efficiency measurements indicate that K3B3O4(OH)4·2H2O is type I phase-matchable. Our calculated results show that the borate groups as well as the waters of hydration determine the NLO properties of K3B3O4(OH)4·2H2O.

Deep Ultraviolet Nonlinear Optical Materials

Deep ultraviolet (absorption edge 6.2 eV) nonlinear optical (NLO) materials are of current interest owing to their technological applications and materials design challenges. Technologically, the materials are used in laser systems, atto-second pulse generation, semiconductor manufacturing, and photolithography. Designing and synthesizing a deep UV NLO material requires crystallographic non-centrosymmetry, a wide UV transparency range, a large second-harmonic generating coefficient (dij > 0.39 pm/V), moderate birefringence (Δn ∼ 0.07), chemical stability and resistance to laser damage, and ease in the growth of large high-quality single crystals. This review examines the known deep UV NLO materials with respect to their crystal structure, band gap, SHG efficiency, laser damage threshold, and birefringence. Finally, future directions with respect to new deep UV NLO materials are discussed.

Bidenticity-Enhanced Second Harmonic Generation from Pb Chelation in Pb3Mg3TeP2O14.

A new ultraviolet nonlinear optical (NLO) material, Pb3Mg3TeP2O14 (PMTP), has been synthesized and characterized. The chiral material exhibits a large second harmonic generation (SHG) response of 13.5 × KDP (600 × α-SiO2), and the shortest absorption edge (250 nm) of reported materials with a strong SHG response (>10 × KDP). PMTP has a three-dimensional crystal structure of corner-shared MgO4, PO4, and TeO6 polyhedra, which form a [TeMg3P2O14]∞ framework. Electronic structure calculations revealed that the stereoactive lone pair on the Pb(2+) cation is critical to producing the substantial NLO response and that the NLO activity is further enhanced by the presence of triply bidentate Te(6+) cations found in Te-O-O-Pb rings.

The Synthesis of the Novel Vacuum Ultraviolet Double Frequency Crystal KBe<sub>2</sub>BO<sub>3</sub>F<sub>2</sub> (KBBF)

KBe2BO3F2 (KBBF) crystal is a sole important and practical ultraviolet nonlinear optical material. It can realize the output of vacuum ultraviolet laser below 200nm with the method of phase-matching. However, it is difficult to grow a practical crystal size with the general growth methods such as fluxed melts, hydrothermal or prism-coupling technique because of the layering growth habit. A reduced-pressure melts growth method was presented to grow bulk KBBF crystal and how to achieve the high quality raw material for growth is a critical factor. In this paper, the influences of syntheses methods of raw material and experiment conditions were discussed, and the best syntheses method was selected.

Energy band gap engineering in borate ultraviolet nonlinear optical crystals: ab initio studies

The development of ultraviolet (UV) nonlinear optical (NLO) crystals demands optical materials with wide energy band gaps. Here we report first-principles studies on the electronic structures in several UV NLO borates with representative structures. Combined with model analysis, we find that the oxygen non-bonding 2p orbitals play an important role on the top of valence bands. The energy band gap can be adjusted by modifying the coordination environment around the oxygen atoms. Under ideal conditions the energy band gaps achieve 9 eV if the non-bonding orbitals are totally eliminated, despite the original values varying from 6.6 to 8.3 eV.

High-efficiency 355 nm generation in barium aluminum borate diflouride (BaAlBO_3F_2)

We demonstrate high-efficiency ultraviolet (UV) laser generation in a nonlinear optical crystal BaAlBO3F2 (BABF); 355 nm UV light was generated by using a type I BABF crystal as a sum-frequency mixing of the fundamental light and the second harmonic from a picosecond Nd:YAG laser operated at a repetition rate of 10 Hz with a pulse duration of 20 ps. An output of 0.635 mJ for the third harmonic was obtained. The conversion efficiency was 26.4%. As far as we know, it was the first time that third-harmonic generation in BABF was achieved. Obviously, the BABF crystal is a promising UV nonlinear optical material because of its relatively large nonlinear coefficient and nonhygroscopicity.

A new promising phosphor, Na3La2(BO3)3:Ln (Ln=Eu, Tb)

We present an efficient way to search a host for ultraviolet (UV) phosphor from UV nonlinear optical (NLO) materials. With the guidance, Na3La2(BO3)3 (NLBO), as a promising NLO material with a broad transparency range and high damage threshold, was adopted as a host material for the first time. The lanthanide ions (Tb3+ and Eu3+)-doped NLBO phosphors have been synthesized by solid-state reaction. Luminescent properties of the Ln-doped (Ln=Tb3+, Eu3+) sodium lanthanum borate were investigated under UV ray excitation. The emission spectrum was employed to probe the local environments of Eu3+ ions in NLBO crystal. For red phosphor, NLBO:Eu, the measured dominating emission peak was at 613nm, which is attributed to 5D0–7F2 transition of Eu3+. The luminescence indicates that the local symmetry of Eu3+ in NLBO crystal lattice has no inversion center. Optimum Eu3+ concentration of NLBO:Eu3+ under UV excitation with 395nm wavelength is about 30mol%. The green phosphor, NLBO:Tb, showed bright green emission at 543 with 252nm excited light. The measured concentration quenching curve demonstrated that the maximum concentration of Tb3+ in NLBO was about 20%. The luminescence mechanism of Ln-doped NLBO (Tb3+ and Eu3+) was analyzed. The relative high quenching concentration was also discussed.