Perfectly Encoding π‐Conjugated Anions in the RE₅(C₃N₃O₃)(OH)₁₂ (RE=Y, Yb, Lu) Family with Strong Second Harmonic Generation Response and Balanced Birefringence

Abstract

Nonlinear optical (NLO) crystal, which simultaneously exhibits strong second‐harmonic‐generation (SHG) response and desired optical anisotropy, is a core optical material accessible to the modern optoelectronics. Accompanied by strong SHG effect in a NLO crystal, a contradictory problem of overlarge birefringence is ignored, leading to low frequency doubling efficiency and poor beam quality. Herein, a series of rare earth cyanurates RE5(C3N3O3)(OH)12 (RE=Y, Yb, Lu) were successfully characterized by 3D electron diffraction technique. Based on a “three birds with one stone” strategy, they enable the simultaneous fulfillment of strong SHG responses (2.5–4.2× KH2PO4), short UV cutoff (ca. 220 nm) and applicable birefringence (ca. 0.15 at 800 nm) by the introduction of rare earth coordination control of π‐conjugated (C3N3O3)3− anions. These findings provide high‐performance short‐wavelength NLO materials and highlight the exploration of cyanurates as a new research area.

A UV solar-blind nonlinear optical crystal with confined π-conjugated groups

“…2d). It is noted that the SHG efficiency of the reported RPNCO is relatively higher than that of previously reported compounds containing π-conjugated rings, such as Y 5 (C 3 N 3 O 3 )(OH) 12 (2.5 × KDP) and Yb 5 (C 3 N 3 O 3 )(OH) 12 (3.8 × KDP), 27 CsAlB 3 O 6 F (2.0 × KDP), 28 CsZn 2 B 3 O 7 (1.5 × KDP), 29 (C 5 H 6 ON) + (H 2 PO 4 ) − (3.0 × KDP), 11 NaRb 0.84 Cs 0.16 HC 3 N 3 O 3 •2H 2 O (3.0 × KDP), 30 (C 4 H 6 N 3 ) + (H 2 PO 3 ) − (2.0 × KDP), 31 and K 3 C 6 N 7 O 3 •2H 2 O (4.0 × KDP). 32 The birefringence value of RPNCO was estimated using a polarizing microscope.…”

KNa2Lu(BO3)2: A Rare-Earth Borate Crystal Characterized by an Enhanced Birefringence and Wide Ultraviolet Transparency Range

“…Figure a illustrates that KNa 2 Lu(BO 3 ) 2 displays a notably short UV cutoff at 204 nm, corresponding to a favorable experimental band gap value of 5.58 eV, as determined via the Kubelka–Munk criterion . Such favorable UV optical characteristic is comparable to that of other rare-earth borates, like KNa 2 La 2 (BO 3 ) 3 (5.3 eV), K 6 NaSrSc 2 (B 5 O 10 ) 3 (5.92 eV), and K 7 CdSc 2 (B 5 O 10 ) 3 (5.26 eV). , Moreover, the IR spectrum of polycrystalline sample is illustrated in Figure b, revealing characteristic absorption bands at approximately 1397, 1347, and 1167 cm –1 , mainly attributed to the asymmetric stretching of [BO 3 ] groups, whereas those observed between 611 and 812 cm –1 primarily originate from the bending vibrations of [BO 3 ] units. − The attributes are in concordance with previously reported results, thereby substantiating its validity on the structural analysis of KNa 2 Lu(BO 3 ) 2.…”

“…Additionally, rare-earth ions readily form bonds with oxygen ions, resulting in the formation of flexible distorted polyhedra, which enhances the polarizability of structural anisotropy. Moreover, several rare-earth cations, particularly Sc 3+ , Y 3+ , La 3+ , Lu 3+ , and Gd 3+ , possess half-occupied 4f orbitals or closed-shell electronic configurations, thus averting d - d or f - f electronic transitions and extending the UV transmission range …”

Polymorphism of Niobium Phosphate Bronze Na4Nb8P4O32Deduced by the Packings of Structural Units: A Centrosymmetric Phase

“…are susceptible to the second-order Jahn–Teller (SOJT) effect, leading to the formation of locally distorted MO 6 octahedra. − These MO 6 octahedra have the tendency to connect with themselves or other octahedral/tetrahedral units such as ZnO 6 , BO 4 , and PO 4 by the oxygen vertices, constructing two-dimensional (2D) layers or three-dimensional (3D) architectures. From the perspective of structure–performance relation, the acentric coordinated environment of MO 6 octahedra offers more possibilities in obtaining noncentrosymmetric and polar structures, which are the prerequisite of nonlinear optical (NLO) and piezoelectric materials. − Moreover, large dipole moments and polarizations from distorted MO 6 octahedra facilitate the generation of strong NLO activity, fast ionic transportation, and excellent photocatalytic performance. − Consequently, d 0 transition metal oxides have been extensively investigated in numerous significant technological fields, including lasers, , battery systems, , catalysis, , and ion exchangers. , Typical examples compass KTiOPO 4 groups, , LiNbO 3 series, , perovskite families, , and polyoxometalates (POMs). , …”