Ultraviolet Crystal with Strong Optical Nonlinearity by Creating Halogen-Centered Secondary Building Blocks

Abstract

Designing new ultraviolet nonlinear optical (NLO) crystals with strong second-harmonic generation (SHG) response and a deep ultraviolet cutoff edge is an unremitting pursuit of scientific researchers, accompanied by the key issues of how to realize a noncentrosymmetric structure with the ideal arrangement of ultraviolet NLO-active genes. Herein, a strategy that creates halogen-centered secondary building blocks with rare-earth atoms was used for further design, and we synthesized rationally an unprecedented NLO crystal Cs 2 La 2 B 10 O 17 Cl 4 exhibiting the largest SHG response (2.1 × KDP) among borates with [B 5 O 11 ] as the fundamental building blocks. The unique role of Cl-centered secondary building blocks in regulating the arrangement of the B− O framework and enhancing nonlinearity was discussed in detail, which will bring the researcher a perspective in designing new NLO crystals.

Centrosymmetric Rb2Sb(C2O4)2.5(H2O)3 and Noncentrosymmetric RbSb2(C2O4)F5: Two Antimony (III) Oxalates as UV Optical Materials

“…More recently, Pan et al have proposed a method named “creating halogen-centered secondary building blocks (SBUs) with rare-earth atoms”, in which halides could increase the probability of producing borates with noncentrosymmetric symmetry to 50%, compared to the overall inorganic compound probability of 15%. This also confirms the role of halogen in the formation of NCS structures . In the two compounds under investigation in this work, the Sb polyhedra and [C 2 O 4 ] 2– units initially form isolated [Sb 2 (C 2 O 4 ) 5 ] 4– clusters in Rb 2 Sb­(C 2 O 4 ) 2.5 (H 2 O) 3 and [Sb 2 (C 2 O 4 )­F 5 ] − clusters in RbSb 2 (C 2 O 4 )­F 5 .…”

Screening Large Birefringent Materials via Halogen Regulation in Ternary d0-Transition Metal Oxyhalides

“…And it has introduced a novel avenue for enhancing the ionic conductivity of electrolyte systems with high salt concentrations . Notably, recent endeavors have been dedicated to the design of novel materials incorporating mixed-anions such as metal chalcohalides, − metal oxysulfides, − and metal oxyhalides, − which have significantly influenced subsequent research directions in optical materials. Among these, metal oxyhalides have emerged as a particularly captivating area of investigation.…”

Hydroxyl-Driven Enhanced Birefringence in Borophosphates

“…In general, the birefringence will be significantly improved by introducing the cations with lone pair electron into the structure. − Meanwhile, the fluorinated tetrahedra always generate a large distortion, which is also beneficial to improve the optical anisotropy of crystals. − In addition, the introduction of hydroxyl can also be deemed as an effective approach to enhance the polarizability anisotropy of the tetrahedra groups, which positively affects the birefringence, − such as AEB 8 O 15 H 4 (AE = Sr, Ca) . Alkali and alkaline-earth metals are free of f–f and d–d electron transition, which ensures the broad penetration in the UV or DUV region, so they have been widely applied in the exploration of UV/DUV optical crystals, − such as Li 3 BP 2 O 8 , K 7 B 2 P 5 O 19 , and CaBPO 5 . − Besides, NH 4 + ion has also been utilized as an “element” to explore new UV/DUV optical materials, and it may enhance the structural stability through the high-strength hydrogen bonds to form compact structures, which will be beneficial to improve the optical properties of compounds. − …”