KCs₂[Pb₂Br₅(HCOO)₂]: A Polar 3D Lead‐Bromide Framework Exhibiting Strong Second‐Harmonic Generation Response

Abstract

The discovery of new nonlinear optical (NLO) crystals with excellent properties is in urgently demand because of their ability to generate coherent light. Herein, we report an unique NLO lead bromide formate, KCs 2 [Pb 2 Br 5 (HCOO) 2 ], which has been synthesized by a mix-solvothermal method. KCs 2 [Pb 2 Br 5 (HCOO) 2 ] exhibits strong phasematching second-harmonic generation (SHG) response (6.5 × KDP), large birefringence (0.16@ 1064 nm), and a wide transparent window in most visible light and mid-IR region. Interestingly, KCs 2 [Pb 2 Br 5 (HCOO) 2 ] features a polar 3D leadbromide framework in which adjacent PbÀ Br layers containing coplanar Pb 6 Br 6 rings are not only parallel to each other, but also orient in the same direction. These oriented arrangements are responsible for the strong SHG response and large birefringence that are elucidated by both local dipole moment and theoretical calculations. This research provides a new strategy to explore subsequent NLO crystals.Nonlinear optical (NLO) crystals are playing an important role in solid-state lasers because of their ability to generate coherent light. [1] As we know, some NLO crystals, including KBe 2 BO 3 F 2 (KBBF), LiB 3 O 5 (LBO), β-BaB 2 O 4 (BBO), KH 2 PO 4 (KDP), KTiOPO 4 (KTP) and AgGaS 2 (AGS), have been applied in the field from deep ultraviolet (DUV) to infrared (IR) region. [2] However, it is still a challenge to synthesis new NLO crystals which simultaneously possesses strong second harmonic generation (SHG) response, good stability, large band gap, high laser damage threshold (LDT) and moderate birefringence to satisfy phase matching. [3] For instance, though AGS has strong SHG response, low LDT has restricted its further practical application in high power lasers. With the development of modern solid-state lasers, their demands on NLO crystals are increased. Therefore, the research has been continuously performed to look for NLO crystals with interesting structures and excellent performances. In recent years, many efforts are focused on inorganic salts such as phosphate, [4] carbonate, [5] borate [6] and sulfate. [7] Borate is of the most attention since its suitable birefringence and flat [BO 3 ] anionic group has high second-order susceptibility. Similar to borate, the presence of planar [CO 3 ] anionic group in carbonate is also of great interest.

A flexible functional module to regulate ultraviolet optical nonlinearity for achieving a balance between a second-harmonic generation response and birefringence

“…Such a strong SHG response is larger than those of most of the recently reported organic–inorganic hybrid UV NLO crystals (Table 1) and can be comparable with those of some well-known UV NLO materials, including NH 4 B 4 O 6 F (∼3 × KDP), 8 M 2 B 10 O 14 F 6 (M = Ca, Sr) (2.5, 2.3 × KDP), 9 ABCO 3 F (A = K, Rb; B = Mg, Ca, Sr) (3–3.6 × KDP), 10,56 LBO (2.2 × KDP) 5 and CLBO (2.4 × KDP). 52 According to the anionic group theory, the SHG response of KLMW is dominated by the flexible π-groups. Although the (C 3 H 2 O 4 ) 2− groups are non-coplanar in order to achieve moderate birefringence, the microscopic second order polarizabilities produced by the (C 3 H 2 O 4 ) 2− groups are superimposed along the c -axis (Fig.…”

New lead-iodide formates with a strong second-harmonic generation response and suitable birefringence obtained by the substitution strategy

“…To our surprise, the crystals we obtained have a completely new structure with excellent NLO performances. After systematic experiments and necessary tests, we report these unique lead-iodide formates, A 2 [PbI 2 (HCOO) 2 ] (A = K, Rb), which exhibit a different lead coordination environment compared with the lead-chloride and lead-bromide formates previously reported, 12,13 the strongest phase-matching SHG response among formates, suitable birefringence and easy growth of large crystals.…”

NaCl·CH4N2O·H2O: An Organic–Inorganic Hybrid Ultraviolet Nonlinear Optical Crystal with Optimized Comprehensive Properties

“…Accordingly, they have become one of the research focuses of NLO materials. In recent years, researchers have discovered a series of excellent NLO crystal materials containing organic planar π-conjugated units, such as C­(NH 2 ) 3 SO 3 F (5 × KDP, 0.133@1064 nm), [C­(NH 2 ) 3 ] 2 PO 3 F (1 × KDP, 0.039@532 nm), (NH 4 ) 2 C 2 O 4 ·H 2 O (0.9 × KDP, 0.1587@546 nm), , [C­(NH 2 ) 3 ] 3 PO 4 ·2H 2 O (1.5 × KDP, 0.055@546.1 nm), (NH 4 )­Sb 2 C 2 O 4 F 5 (1.1 × KDP, 0.111@546 nm), Cs 3 Pb 2 (CH 3 COO) 2 I 5 (8 × KDP, 0.26@1064 nm), KCs 2 [Pb 2 Br 5 (HCOO) 2 ] (6.5 × KDP, 0.16@1064 nm), NaHC 4 O 4 ·H 2 O (2.3 × KDP, 0.52@1064 nm), and RbNa­(HC 3 N 3 O 3 )·2H 2 O­(5.3 × KDP, 0.239@546.1 nm) . However, except some crystals containing guanidine, a number of these crystals exhibit a relatively small band gap that obstructs the application in the UV region.…”