Two-dimensional (2D) materials have been well developed for polarization-sensitive photodetection, while new 2D members used in shortwave region (>2.5 eV) still remain scarce. The family of 2D hybrid perovskite ferroelectrics, in which the coupling of spontaneous polarization (P s ) and light benefits dissociation of photoinduced carriers, has shown great potential in this portfolio. Here, we report a new 2D hybrid perovskite ferroelectric, [CH 3 (CH 2 ) 3 NH 3 ] 2 (CH 3 NH 3 )Pb 2 Br 7 (1), which exhibits a superior P s of 3.6 μC/cm 2 and a relatively wide bandgap (∼2.55 eV). The unique 2D perovskite motif results in an intrinsic anisotropy of optical absorption (the ratio α c /α a ≈ 1.9 at 405 nm), involving its polarizationsensitive activity. As expected, the strongest photoresponses were observed along the c-axis (i.e., parallel to P s ), along with a large dichroism ratio (I ph c /I ph a ≈ 2.0) and highly sensitive detectivity up to ∼10 9 Jones. Further, crystal-device of 1 shows a fast responding rate (∼20 μs) and excellent antifatigued merits. As pioneering work, 1 is the first polarization-sensitive ferroelectric in the new branch of 2D hybrid perovskites. Such intriguing behaviors make 1 a potential candidate for the shortwave polarized-light detection, which also sheds light on new functionalities for future optoelectronic application of hybrid perovskites.

The non-π-conjugated sulfate system has long been overlooked as potential deep-UV nonlinear optical (NLO) materials. Here we report two asymmetric anhydrous sulfates, namely, NH 4 NaLi 2 (SO 4 ) 2 (Ι) and (NH 4 ) 2 Na 3 Li 9 (SO 4 ) 7 (Π), which consist of non-πconjugated [SO 4 ] 2− anions. Their single crystals can be readily grown by a facile evaporation method from water solution. Both sulfates are transparent down to the deep-UV region. Interestingly, there is a large NLO gap between I and Π, with phase-matching NLO responses of 1.1 and 0.5 times that of the benchmark KH 2 PO 4 , respectively. The first-principles studies reveal that the non-π-conjugated [SO 4 ] 2− anions are the dominate NLOactive groups, and the large NLO gap between I and Π can be ascribed to the nonbonding O 2p orbitals of different orientations in the crystallographically independent S1O 4 groups. This work provides an innovative non-πconjugated source that is distinct from the traditional πconjugated ones for deep-UV NLO materials.

It is challenging to explore deep-ultraviolet (deep-UV) nonlinear optical (NLO) materials that can achieve a subtle balance between deep-UV transparency and high NLO activity. Known deep-UV NLO materials are almost exclusively limited to borates, except few newly discovered phosphates despite their small NLO activities. Here we report two asymmetric phosphates, RbBa2(PO3)5 (I) and Rb2Ba3(P2O7)2 (II), which feature [PO3]∞ chains and [P2O7](4-) dimers formed by condensation of [PO4](3-) units, respectively. Remarkably, I achieves the desired balance, with the shortest deep-UV absorption edge at 163 nm and the largest NLO activity of 1.4 × KDP (KH2PO4) in deep-UV NLO phosphates. According to first-principles calculations, the enhanced macroscopic SHG response of I can be attributed to the [PO3]∞ chains which exhibit significantly larger microscopic SHG coefficients as compared with the [P2O7](4-) dimers.

A new beryllium-free borate Rb3Al3B3O10F has been synthesized and characterized by single-crystal X-ray diffraction. It features a framework structure consisting of alveolate [Al3(BO3)3OF]∞ layers tightly bound via Al-O and Al-F bridged bonds, with the in-layer [BO3](3-) groups in nearly coplanar and aligned arrangement. This compound is transparent down to 200 nm and is phase-matchable with a powder second-harmonic generation efficiency of 1.2 times that of KH2PO4. Remarkably, it exhibits a strong interlayer bonding which is about one order larger than that of the benchmark KBe2BO3F2, thus no layering tendency was observed during the crystal growth. In addition, it is nonhygroscopic and thermally stable up to ∼1462 K. These attributes make Rb3Al3B3O10F a promising nonlinear optical crystal in the deep-ultraviolet region. First-principles calculations, combined with the anionic group theory, were adopted to rationalize the optical properties.

Multiaxial molecular ferroelectrics, in which multiple-directional switching of spontaneous polarization creates diverse properties, have shown many intriguing advantages, making them indispensable complements to conventional inorganic oxides. Despite recent blooming advances, multiaxial molecular ferroelectric with bulk photovoltaic effects still remains a huge blank. Herein, we report a biaxial lead halide ferroelectric, EA 4 Pb 3 Br 10 (1, EA = ethylammonium), which adopts the unique trilayered perovskite motif with a high Curie temperature of ∼384 K. Particularly, for 1, the distinct symmetry breaking with 4/mmmFmm2 species leads to the emergence of four equivalent polarization directions in the ferroelectric phase. Based on its biaxial nature, the bulk photovoltaic effect of 1 can be facilely tuned between such multiple directions through electric poling. As far as we know, this is the first report on biaxial hybrid perovskite ferroelectric showing directionally tunable photovoltaic activity. This work provides an avenue to control the bulk physical properties of multiaxial molecular ferroelectrics, and highlights their potential for further applications in the field of smart devices.

A chiral one-dimensional organic–inorganic hybrid perovskite exhibits white-light emission with ultrahigh CRI.

Although two-dimensional (2D) metal-halide double perovskites displayversatile physical properties due to their huge structural compatibility,r oom-temperature ferroelectric behavior has not yet been reported for this fascinating family. Here,w ed esigned ar oom-temperature ferroelectric material composed of 2D halide double perovskites,(chloropropylammonium) 4 AgBiBr 8 ,u sing an organic asymmetric dipolar ligand. It exhibits concrete ferroelectricity,i ncluding aC urie temperature of 305 Ka nd an otable spontaneous polarization of % 3.2 mCcm À2 ,triggered by dynamic orderingofthe organic cation and the tilting motion of heterometallic AgBr 6 /BiBr 6 octahedra. Besides,t he alternating arrayo fi norganic perovskite sheets and organic cations endows large mobility-lifetime product (mt = 1.0 10 À3 cm 2 V À1)f or detecting X-ray photons, which is almost tenfold higher than that of CH 3 NH 3 PbI 3 wafers.A sf ar as we know,t his is the first study on an X-raysensitive ferroelectric material composed of 2D halide double perovskites.O ur findings affordapromising platform for exploring new ferroelectric materials toward further device applications.

It is of great difficulty to obtain deep-UV transparent materials with enhanced second harmonic generation (SHG), mainly limited by the theoretically poor transparency of these materials in the deep-UV spectral region. Here we report a new noncentrosymmetric, deep-UV transparent phosphate RbNaMgPO, which undergoes a thermo-induced reversible phase transition (at a high temperature of 723 K) and correspondingly an evident SHG enhancement up to ∼1.5 times. The phase transition is aroused by the twist of [PO] dimers with deviation from the P-O-P equilibrium positions. Theoretical analyses reveal that the enhanced SHG can be ascribed to the thermo-induced collective alignment of SHG-active [PO] dimers along the polar axis of high-temperature phase. This work provides an unprecedented physical routine (to SHG-enhanced materials) that is distinguished from the traditional one by chemical design and synthesis.