Fine-Tuning Solid State Luminescence Properties of Organic Crystals via Solid Solution Formation: The Example of 4‑Iodothioxanthone–4-Chlorothioxanthone System

Solid solutions with fine-tunable photoluminescence have been obtained in a 4-iodothioxanthone–4-chlorothioxanthone system. Both pure components are room-temperature luminophors demonstrating different luminescence properties. It was discovered that in the 4-chlorothioxanthone structure, up to half of the molecules can be replaced by the iodo analogue obtaining solid solutions in the respective composition range. Despite this solid solution existing in such a large composition range, the variation of the luminescence spectra is not substantial. In the 4-iodothioxanthone structure, only up to ∼20% of the molecules can be replaced by the chloro analogue before the composition limit of this solid solution is reached. In contrast, there is a strong composition-dependent response of the luminescence. A considerable change in luminescence spectra is observed even if only a few mol % of the opposite component is added. The spectra of mechanical mixtures of pure components are different from those of the solid solutions, which demonstrates the unique behavior of the newly obtained solid phases. This study shows great potential to use solid solution engineering in the organic solid state to tune material properties in a continuum as opposed to other crystal engineering approaches, leading to property tunability in a stepwise fashion

Amorphous Calcium Phosphate and Amorphous Calcium Phosphate Carboxylate: Synthesis and Characterization

Amorphous calcium phosphate (ACP) is the first solid phase precipitated from a supersaturated calcium phosphate solution. Naturally, ACP is formed during the initial stages of biomineralization and stabilized by an organic compound. Carboxylic groups containing organic compounds are known to regulate the nucleation and crystallization of hydroxyapatite. Therefore, from a biomimetic point of view, the synthesis of carboxylate ions containing ACP (ACPC) is valuable. Usually, ACP is synthesized with fewer steps than ACPC. The precipitation reaction of ACP is rapid and influenced by pH, temperature, precursor concentration, stirring conditions, and reaction time. Due to phosphates triprotic nature, controlling pH in a multistep approach becomes tedious. Here, we developed a new ACP and ACPC synthesis approach and thoroughly characterized the obtained materials. Results from vibration spectroscopy, nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), true density, specific surface area, and ion release studies have shown a difference in the physiochemical properties of the ACP and ACPC. Additionally, the effect of a carboxylic ion type on the physiochemical properties of ACPC was characterized. All of the ACPs and ACPCs were synthesized in sterile conditions, and in vitro analysis was performed using MC-3T3E1 cells, revealing the cytocompatibility of the synthesized ACPs and ACPCs, of which the ACPC synthesized with citrate showed the highest cell viability

Unraveling the Structure and Properties of Layered and Mixed ReO₃–WO₃ Thin Films Deposited by Reactive DC Magnetron Sputtering

Tungsten trioxide (WO3) is a well-known electrochromic material with a wide band gap, while rhenium trioxide (ReO3) is a “covalent metal” with an electrical conductivity comparable to that of pure metals. Since both WO3 and ReO3 oxides have perovskite-type structures, the formation of their solid solutions (ReO3–WO3 or RexW1–xO3) can be expected, which may be of significant academic and industrial interest. In this study, layered WO3/ReO3, ReO3/WO3, and mixed ReO3–WO3 thin films were produced by reactive DC magnetron sputtering and subsequent annealing in air at 450 °C. The structure and properties of the films were characterized by X-ray diffraction, optical spectroscopy, Hall conductivity measurements, conductive atomic force microscopy, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoemission spectroscopy. First-principles density functional theory calculations were performed for selected compositions of RexW1–xO3 solid solutions to model their crystallographic structure and electronic properties. The calculations predict metallic conductivity and tetragonal distortion of solid solutions in agreement with the experimental results. In contrast to previously reported methods, our approach allows us to produce the WO3–ReO3 alloy with a high Re content (>50%) at moderate temperatures and without the use of high pressures