Enhancement of Ferroelectricity for Orthorhombic (Tb0.861Mn0.121)MnO3-δ by Copper Doping

Complexing Eu3+/Tb3+ in a Nanoscale Postmodified Zr-MOF toward Temperature-Modulated Multispectrum Chromism

In recent years, extensive research has been directed toward the successful preparation of nanoscale luminescent thermometers with high sensitivities operative in a broad temperature range. To achieve this goal, we have devised a unique design and facile multistep synthesis of Zr-ctpy-NMOF@Tb_xEu_y compounds by confining Ln-complexes (Ln = Eu³⁺/Tb³⁺) into a robust nanoscale Zr-NMOF (MOF-808) via postsynthetic modification. Covalent grafting of 4-(4'-carboxyphenyl)-2,2':6,2″terpyridine ligand (ctpy) with a high triplet state energy and corresponding immobilization of bimetallic Ln³⁺ ions resulted in yellow light-emitting Zr-ctpy-NMOF@Tb_1.66Eu_0.14 to achieve a sensitivity of 5.2% K^-1 (thermal uncertainty dT < 1 K) operative over a broad temperature range of 25-400 K. To defeat the odds related to the detection of minute temperature changes using luminescent materials, we prepared a white light-emitting Zr-ctpy-NMOF@Tb_1.4Eu_0.31 that showed temperature-modulated multispectrum chromism where the color drastically changes from green (at 25 K, Q.Y.: 20.21%) to yellowish-green (at 200 K, Q.Y.: 23.13%) to white (at 300 K, Q.Y.: 26.4%) to orange (at 350 K, Q.Y.: 26.93%) and finally red (at 400 K, Q.Y.: 28.2%) with a high energy transfer efficiency of 49.8%, which is further supported by electron-phonon coupling.

Terbium-Doped and Dual-Passivated γ-CsPb(I1- x Brx )3 Inorganic Perovskite Solar Cells with Improved Air Thermal Stability and High Efficiency

Realizing photoactive and thermodynamically stable all-inorganic perovskite solar cells (PSCs) remains a challenging task within halide perovskite photovoltaic (PV) research. Here, a dual strategy for realizing efficient inorganic mixed halide perovskite PV devices based on a terbium-doped solar absorber, that is, CsPb_{1- x} Tb_x I₂ Br, is reported, which undertakes a bulk and surface passivation treatment in the form of CsPb_{1- x} Tb_x I₂ Br quantum dots, to maintain a photoactive γ-phase under ambient conditions and with significantly improved operational stability. Devices fabricated from these air-processed perovskite thin films exhibit an air-stable power conversion efficiency (PCE) that reaches 17.51% (small-area devices) with negligible hysteresis and maintains >90% of the initial efficiency when operating for 600 h under harsh environmental conditions, stemming from the combined effects of the dual-protection strategy. This approach is further examined within large-area PSC modules (19.8 cm² active area) to realize 10.94% PCE and >30 days ambient stability, as well as within low-bandgap γ-CsPb_0.95 Tb_0.05 I_2.5 Br_0.5 (E_g  = 1.73 eV) materials, yielding 19.01% (18.43% certified) PCE.

Crystal and Magnetic Structures and Properties of (Lu1- xMn x)MnO3 Solid Solutions

(Lu_{1- x}Mn _x)MnO₃ solid solutions, having the perovskite-type structure and Pnma space group, with 0 ≤ x ≤ 0.4 were synthesized by a high-pressure, high-temperature method at 6 GPa and about 1670 K from Lu₂O₃ and Mn₂O₃. Their crystal and magnetic structures were studied by neutron powder diffraction. The degree of octahedral MnO₆ tilting decreases in (Lu_{1- x}Mn _x)MnO₃ with increasing x. Only the incommensurate (IC) spin structure with a propagation vector of k = ( k₀, 0, 0) and k₀ ≈ 0.44 remains in (Lu_0.9Mn_0.1)MnO₃ in the whole temperature range below the Neel temperature T_N = 36 K, and the commensurate noncollinear E-type structure that has been reported in the literature for undoped o-LuMnO₃ is not observed. (Lu_{1- x}Mn _x)MnO₃ samples with 0.2 ≤ x ≤ 0.4 have a ferrimagnetic structure with a propagation vector of k = (0, 0, 0) and ferromagnetic (FM) ordering of Mn³⁺ and Mn⁴⁺ cations at the B site, which are antiferromagnetically coupled to a noncollinear predominantly FM arrangement of Mn²⁺ at the A site. The ferrimagnetic Curie temperature, T_C, increases monotonically from 67 K for x = 0.2 to 118 K for x = 0.4. Magnetic and dielectric properties of (Lu_{1- x}Mn _x)MnO₃ and a composition-temperature phase diagram are also reported.

Mn Self-Doping of Orthorhombic RMnO3 Perovskites: (R0.667Mn0.333)MnO3 with R = Er-Lu

Orthorhombic rare-earth trivalent manganites RMnO₃ (R = Er-Lu) were self-doped with Mn to form (R_0.667Mn_0.333)MnO₃ compositions, which were synthesized by a high-pressure, high-temperature method at 6 GPa and about 1670 K from R₂O₃ and Mn₂O₃. The average oxidation state of Mn is 3+ in (R_0.667Mn_0.333)MnO₃. However, Mn enters the A site in the oxidation state of 2+, creating the average oxidation state of 3.333+ at the B site. The presence of Mn²⁺ was confirmed by hard X-ray photoelectron spectroscopy measurements. Crystal structures were studied by synchrotron powder X-ray diffraction. (R_0.667Mn_0.333)MnO₃ crystallizes in space group Pnma with a = 5.50348(2) Å, b = 7.37564(1) Å, and c = 5.18686(1) Å for (Lu_0.667Mn_0.333)MnO₃ at 293 K, and they are isostructural with the parent RMnO₃ manganites. Compared with RMnO₃, (R_0.667Mn_0.333)MnO₃ exhibits enhanced Néel temperatures of about T_N1 = 106-110 K and ferrimagnetic or canted antiferromagnetic properties. Compounds with R = Er and Tm show additional magnetic transitions at about T_N2 = 9-16 K. (Tm_0.667Mn_0.333)MnO₃ exhibits a magnetization reversal or negative magnetization effect with a compensation temperature of about 16 K.