The extraordinary thermal stability of [NH₂CHNH₂]₃Bi₂I₉ (FA₃Bi₂I₉) crystals, up to around 600 K, has been enhanced by using the evaporating method. DSC measurements have revealed reversible structural phase transitions: at 203 K (Phase I → Phase II), 173 K (II → III), 134.7 K (III → IV), 131.4 K (IV → V), and 120 K (V → VI). The crystal structures of FA₃Bi₂I₉ adopt the polar space groups P6₃mc at 220 K (Phase I) and Cmc2₁ at 190 K (Phase II). The pyroelectric current (I_pyr) measured in the temperature range covering all the phases of FA₃Bi₂I₉ confirmed their polar nature. The reversibility of the spontaneous polarization in each phase has been confirmed by the observed hysteresis loops. All the phase transitions are dielectrically active. The dielectric response (ε*(ω,T) close to 134.7 and 131.4 K) is characteristic of ferroelectrics with a critical slowing-down process. Optical bandgaps estimated from the UV-vis measurements and calculated using the DFT method are equal to 1.85 and 1.89 eV, respectively. On the basis of the structural, dielectric, and spectroscopic results, the molecular mechanisms of the phase transitions have been proposed.

We report the physicochemical characteristics of a novel Sb-based formamidinium ferroelectric material, (NH₂CHNH₂)₃Sb₂I₉ (FAIA). FAIA crystallizes at room temperature in the hexagonal P6₃mc space group. The crystal structure of FAIA is isomorphic to that of its bismuth analog, [NH₂CHNH₂]₃Bi₂I₉ (FAIB), which is characterized by a zero dimensional (0D) anionic network (discrete bioctahedral units). From the DSC results three phase transitions (PT) have been found for FAIA: at 187.4/189 K (phase I ↔ phase II), 177.6/177.9 K (II ↔ III) and 148.2/152.3 K (III ↔ IV). The compound exhibits ferroelectricity in the room temperature phase I and in the successive temperature phases (II and III). The spontaneous polarization (P_S = 0.5 × 10⁻² μC cm⁻²) reversibility has been confirmed by the presence of the ferroelectric hysteresis loops and pyroelectric measurements. The origin of ferroelectricity is discussed in terms of the cationic dynamics. This material may be considered as a semiconductor (σ ∼ 10⁻⁶ S m⁻¹, 300 K).

Gadolinium-doped nanoparticles (NPs) are regarded as promising luminescent probes. In this report, we studied details of toxicity mechanism of low doses of NaGdF₄-based fluorescent nanoparticles in activated RAW264.7, J774A.1 macrophages. These cell lines were specifically sensitive to the treatment with nanoparticles. Using nanoparticles of three different sizes, but with a uniform zeta potential (about −11 mV), we observed rapid uptake of NPs by the cells, resulting in the increased lysosomal compartment and subsequent superoxide induction along with a decrease in mitochondrial potential, indicating the impairment of mitochondrial homeostasis. At the molecular level, this led to upregulation of proapoptotic Bax and downregulation of anti-apoptotic Bcl-2, which triggered the apoptosis with phosphatidylserine externalization, caspase-3 activation and DNA fragmentation. We provide a time frame of the toxicity process by presenting data from different time points. These effects were present regardless of the size of nanoparticles. Moreover, despite the stability of NaGdF₄ nanoparticles at low pH, we identified cell acidification as an essential prerequisite of cytotoxic reaction using acidification inhibitors (NH₄Cl or Bafilomycin A1). Therefore, approaching the evaluation of the biocompatibility of such materials, one should keep in mind that toxicity could be revealed only in specific cells. On the other hand, designing gadolinium-doped NPs with increased resistance to harsh conditions of activated macrophage phagolysosomes should prevent NP decomposition, concurrent gadolinium release, and thus the elimination of its toxicity.

Here we report a method for coating of hydrophobic nanocrystals (NCs) with a thin silica layer. By using this approach 11 nm NaGdF₄ NCs were coated with a mesoporous silica shell thinner than 20 nm resulting in highly monodisperse core–shell nanocomposite particles smaller than 50 nm. The synthetic protocol used here is based on the two-phase system that ensures high repeatability of the nanoparticle morphology and can be conveniently adapted for large-scale production. The use of an organic solvent as a diluent for tetraethoxysilane allows us to control not only the thickness, but also the porosity of the uniform silica shell. This procedure can be applied for coating NCs of various sizes and can be generalized to encapsulate other nanocrystals, e.g. semi-conductor quantum dots, into silica spheres. Furthermore, it allows facile surface modification with –NH₂ groups that can be then used to conjugate biomolecules to the nanoparticle surface, as well as straightforward incorporation of various organic molecules (e.g. dyes or drugs) into the silica shell during its growth. To demonstrate potential applications up-converting NaGd_0.80Yb_0.18Er_0.02F₄ NCs were used as cores and zinc phthalocyanine was incorporated into the silica shell as a photosensitizer. Under irradiation with a 980 nm laser diode efficient generation of singlet oxygen was observed indicating that such nanocomposite particles have the capability to be used for photodynamic therapy.

Novel lead-free ferroelastic materials, (C ₃ N ₂ H ₅ ) ₃ Sb ₂ I ₉ and (C ₃ N ₂ H ₅ ) ₃ Bi ₂ I ₉ , exhibit rich sequences of phase transitions and reveal semiconducting properties.

Unique organic scaffold to study how subtle structural differences affect the slow magnetic relaxation inS= ½ Cu(ii) systems.