Nonlinear optical (NLO) materials have recently aroused great interest owing to their capability of frequency conversion in solid-state lasers. Herein, we report an acentric zinc germanate K2ZnGe2O6 obtained successfully through spontaneous crystallization methods. It affords a novel three-dimensional (3D) framework comprised of [GeO4] and [ZnO4] motifs with K atoms located in the tunnels. K2ZnGe2O6 displays a moderate second-harmonic-generation (SHG) intensity (0.73 × KDP) with phase-matchable behavior. Optical characterization demonstrated that it has a UV cutoff edge located at 368 nm with a large energy band of 3.23 eV, accompanied by a wide transmission window, covering a 3–5 μm atmospheric window. Moreover, thermal properties implied that it possesses intriguing thermal stability of 987 °C and a congruent melting nature. Additionally, first-principles calculations unveiled that the NLO performance was primarily attributed to the collective effect of [GeO4] and [ZnO4] building units. These findings indicate that K2ZnGe2O6 is a potential NLO crystal.

Nonlinear optical (NLO) crystals have aroused burgeoning interest in recent years owing to their frequency conversion properties and versatile optoelectronic applications. Nevertheless, a current challenge is to excavate NLO crystals with superior overall performance, especially in configurationally rigid silicates. Herein, a new NLO bismuth silicate, Cs2Bi2OSi2O7 (CBSO), was successfully synthesized, which features a 3D structure containing rare face-sharing [BiO5] pyramids and [SiO4] groups. The introduction of highly polarized Bi3+ cations resulted in large induced polarization and an enhanced second harmonic generation (SHG) intensity of 3.5 KDP. Remarkably, CBSO fully meets the precedent conditions for NLO applications, including a wide transparent window, suitable birefringence (0.044 at 1064 nm), good thermal stability with congruent-melting behavior, and facile crystal growth. Besides, first-principles calculations were performed to elucidate the structure–property relationship of CBSO. These observations demonstrate that CBSO is a promising NLO material and provide new inspiration for designing novel SHG-active compounds in strongly covalent systems.

A quaternary nonlinear-optical (NLO) zinc germanate, Rb2ZnGe2O6 (RZGO), was prepared from its stoichiometric melts, which belongs to the noncentrosymmetric space group C2221 (No. 20) and features a 3D framework formed by GeO4 tetrahedra, ZnO4 tetrahedra, and Rb+ cations filling into the void space. RZGO displays a good phase-matchable second-harmonic-generation (SHG) intensity similar to that of KH2PO4. The UV cutoff edge for RZGO was found to be approximately 0.37 μm with a broad optical band gap of 3.22 eV, indicating a large laser-induced damage threshold. Further characterizations suggested that this compound displays an excellent thermal stability (1014 °C) and melts congruently. Besides, theoretical analysis was also implemented to investigate the electronic structures and effective NLO coefficients as well as the origin of the observed SHG response for RZGO. The present study can enrich the diversity of acentric germanate structures and pave the way for the synthesis of new NLO compounds.

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Polymorphism is crucial for unraveling crystallization mechanism, predicting crystal structure and discovering novel materials. A new high-symmetric polymorph of Li2TeMo3O12, α-Li2TeMo3O12, was identified successfully by using a spontaneous crystallization technique,...