Isoreticular Design of KTiOPO₄-Like Deep-Ultraviolet Transparent Materials Exhibiting Strong Second-Harmonic Generation

Abstract

Second-harmonic generation (SHG) is of great technological importance for applications in nonlinear optics, but it remains challenging to engineer large SHG responses in the short-wavelength ultraviolet (UV) region owing to competing microstructure requirements. Herein, we report the first examples of d0 transition-metal-based (TM-based) deep-UV-transparent nonlinear optical (NLO) crystals MOF4H2 (M = Zr (ZOF), Hf (HOF)), which exhibit unprecedented short UV absorption edges (below 190 nm). Evolving from the KTiOPO4 (KTP) structure by an isoreticular node substitution strategy, the three-dimensional frameworks of ZOF and HOF consist of corner-sharing [MO2F6] moieties that are new functional units in deep-UV NLO material design, conferring wide UV transparency and strong phase-matchable SHG response (2.2 × KH2PO4 (ZOF) and 1.8 × KH2PO4 (HOF) at 1064 nm). Such d0-TM-based [MO2F6] polyhedra preclude deleterious d–d electronic transitions, resulting in significantly blue-shifted UV absorption edges of ZOF and HOF (<190 nm). The d0-TM-based [MO2F6] polyhedra introduced in this work offer a new perspective in the construction of deep-UV transparent NLO materials, demonstrating the feasibility of an isoreticular design strategy in developing functional NLO materials.

Toward Large Second-Harmonic Generation and Deep-UV Transparency in Strongly Electropositive Transition Metal Sulfates

“…Overall, these studies reveal that the linear optical properties of ZFSO and HFSO primarily arise from the [ZrO 4 F 4 ]/[HfO 4 F 4 ] 4d 0 /5d 0 TM-based polyhedra and the [SO 4 ] anionic tetrahedra. To clearly demonstrate the influence of the two types of SBUs on the bandgaps, we compared the electronic structures of ZFSO/HFSO with ZrOF 4 H 2 /HfOF 4 H 2 , which possess similar compositions of d 0 -TM oxyfluoride polyhedra but show different behavior near the Fermi level. The bottom of the CB in the aforementioned four compounds mainly consists of Zr/Hf d orbitals.…”

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

“…The ultraviolet (UV) nonlinear optical (NLO) crystal is the core and urgently required device in the all-solid-state laser industry, which is capable of converting the finite incident light source to a shorter wavelength spectral range based on the multistage nonlinear process. − Although numerous efforts have been done for decades, only a few UV NLO crystals have been proven feasible in practical application since three crucial but mutually restrictive optical indexes that are determined by different microstructures are needed to be met simultaneously, − that is, large second-harmonic generation (SHG) response (>1 × KDP) with a noncentrosymmetric crystal structure as a prerequisite, short cutoff edge (<200 nm), and appropriate birefringence to realize phase matching.…”

Ce3F4(SO4)4: cationic framework assembly for designing polar nonlinear optical material through fluorination degree modulation

“…Nonlinear optical (NLO) materials with second-harmonic generation (SHG) properties have important applications in advanced laser technology owing to their frequency conversion abilities. [1][2][3][4][5][6][7][8] A series of state-of-the-art NLO crystals has been used practically from the ultraviolet (UV) region to the infrared (IR) region, as exemplified by KBe 2 B 2 O 6 F 2 (KBBF), 9 LiB 3 O 5 (LBO), 10 LiNbO 3 , 11 KTiOPO 4 (KTP), 12 and AgGaQ 2 (Q = S, Se). 13 The paramount precondition for producing a SHG response is the crystallographic noncentrosymmetric (NCS) structure of crystalline materials.…”