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Herein, for developing colored photocatalysts, calcium manganese oxide (Ca–Mn–O) film and powder samples are synthesized by a sol–gel method using acetylacetone (acac) or citric acid as a chelating agent, and their color and photocatalytic properties are evaluated. Thin‐film X‐ray diffraction experiments clarify the precipitation of Ca–Mn–O phases, such as Ca3Mn2O7 (Ca/Mn = 1.5) and Ca2MnO4 (Ca/Mn = 2), in the film samples with drop‐cast coating. These films strongly absorb all visible light due to the interband transition between O 2p and Mn 3d orbitals, resulting in dark gray coloration. By testing photocatalytic activities using methylene blue dyes, it is revealed that the film sample (acac, 4‐drops) exhibits photocatalytic activities, which makes Ca–Mn–O films dual functional with photocatalytic functions and coloration. [ABSTRACT FROM AUTHOR]

Herein, lead‐free, mixed‐halide perovskites of cesium bismuth bromide/iodide are synthesized by a hydrothermal method, and their structures and optical properties of the solid solution compounds are examined. The synthesized compounds exhibit X‐ray diffraction patterns similar to that of trigonal Cs3Bi2Br9 (CBB), whose reflections are shifted to lower angles depending on the experimental iodine content. Very interestingly, even with the excessive introduction of iodine content in nominal, the symmetry of the crystals is kept to be trigonal, indicating that bromide CBB and iodide Cs3Bi2I9 (CBI) are crystallographically mixed in a facile way, although the stable crystal form of CBI is hexagonal. The optical properties of bandgap energy Eg and photoluminescence (PL) for the synthesized crystals are also examined. It is found that Eg decreases and PL peak position is correspondingly shifted to a longer wavelength with an increase in the experimental iodine content due to their band‐to‐band transitions. Moreover, first‐principles calculation suggests the reduction of Eg with iodine content and the varied nature of band structure from direct (trigonal CBB) to indirect (trigonal CBI) transition. These novel findings can make the proposed strategy successful for developing lead‐free, mixed‐halide Bi‐based perovskite crystals with the tunability of their optical properties. [ABSTRACT FROM AUTHOR]

Currently, data‐driven approaches for exploring novel materials are garnering significant attention with the expectation of accelerating material development cycles and understanding materials from various aspects. This short article presents a supervised prediction model for the emission intensity ratio of 5D0–7F2 and 5D0–7F1 transition of Eu3+ ions, called an "asymmetry ratio", which determines the color purity of the red region of Eu3+ photoluminescence in perovskite phosphors. The model is developed using a dataset of 296 samples and 203 descriptors for Eu3+‐doped perovskite. The accuracy of the prediction model trained by the dataset is statistically evaluated, which validates its sufficiently high prediction performance. Furthermore, the prediction model's performance is properly assessed by synthesizing a Eu3+‐doped NaLaInNbO6 compound, which is unknown as a red phosphor, and by comparing the experimental asymmetry ratio for this compound with that predicted by the predictor, which exhibits satisfactory agreement. [ABSTRACT FROM AUTHOR]

In this study, Eu3+- and alkali-ion (M+)-codoped Sr2CaWO6:x (Eu3+, M+) (x = 0.01–0.10) were synthesized via a solid-state reaction. The effects of different Sr/Ca ratios, types of monovalent metal ions (M+ = Na+, K+, and Li+), and doping concentrations were systematically investigated. The crystalline phase, photoluminescence (PL) properties, lattice site occupied by the Eu3+ ion, Eu3+ site distribution, and site-selective PL properties were evaluated by x-ray diffraction, PL/photoluminescence excitation (PLE) spectroscopy with a monochromatic light source, PL quantum efficiency (QE) measurements, and high-resolution PL/PLE spectroscopy with a wavelength-tunable laser. A dependence of the PL asymmetry ratio for the 5D0–7F1,2 transitions on the Sr/Ca ratio was identified and quantified for the first time. Based on the site-selective PL measurements, this behavior was ascribed to the enhancement of Eu3+ local distortion by Sr2+ substitution at the A site at lower Sr/Ca ratios (<2) and to the high symmetry of the ligand structure of EuO6 octahedra owing to Ca2+ substitution at the B site at higher Sr/Ca ratios (>2). The PLE results provided insight into the Eu3+ site distribution, which explained the orange-red PL and PL QEs of the synthesized phosphors. [ABSTRACT FROM AUTHOR]

In this study, Eu3+ and K+ co‐doped Ca3WO6 double perovskite, a high‐color‐purity red phosphor, is quantitatively investigated using synchrotron X‐ray diffraction Rietveld refinement, energy dispersive X‐ray spectroscopy, and high‐resolution PL spectroscopy. The Eu3+ fluorescence line‐narrowing (FLN) results, used to estimate the Eu3+ occupation at given sites (so‐called A and B sites) in the host crystal (A2BMO6; A, B = Ca; M = W), reveal that the Eu3+ ions have a twin distribution in both the A and B sites with high asymmetry ratios of ΛA = 9.7 and ΛB = 10.7, respectively. More interestingly, at lower Eu3+ doping levels, the ions are predominantly located at the B sites (≈75%), indicating that the high color purity of Ca3WO6:(Eu3+, K+) is mainly caused by the high asymmetry ratios of the Eu3+ sites. Rietveld refinement combined with the FLN technique provides more reliable results for increasing the Eu3+ substitution at the A site with Eu3+ and K+ doping concentrations, which lower the lattice energy of Ca3WO6:(Eu3+, K+). The structural distortions owing to K+ co‐doping in terms of the quadratic elongation and bond‐angle variance exhibit good correlations with the Ca(Eu)O12 A‐site cuboctahedra and Ca(Eu)O6 B‐site octahedra, partially accounting for the higher Λ values. [ABSTRACT FROM AUTHOR]

A series of β‐SiAlON:Eu2+ phosphors were synthesized from single‐source precursors, perhydropolysilazane chemically modified with Al(OCH(CH3)2)3, AlCl3, and EuCl2. The single‐source precursors were converted to β‐SiAlON:Eu2+ phosphors by pyrolysis under flowing N2 or NH3 at 1000°C, followed by heat treatment at 1800°C under an N2 gas pressure at 980 kPa. By varying the molar ratio of the chemical modifiers, β‐SiAlON:Eu2+ with the compositions close to the theoretical ones expressed as Si6−zAlzOz−2yN8−z+2y:yEu2+ were synthesized, where the z values and Eu2+ contents were controlled in the ranges of.44–.78 and.35–1.48 mol%, respectively. The polymer‐derived β‐SiAlON:Eu2+ phosphors exhibited green emission under excitation at 460 nm attributed to the 4f7–4f6(7f3)5d1 transition of dopant Eu2+. High‐angle annular dark‐field‐scanning transmission microscopy analysis confirmed that the doped‐Eu2+ existed interstitially within the channels along the c axis of host β‐SiAlON. Compared with the conventional powder metallurgy route, the polymer‐derived ceramic route in this study offers some advantages in the grain growth of host β‐SiAlON and photoluminescence properties in terms of green emission intensity under excitation at 460 nm, and the highest intensity was achieved for the polymer‐derived β‐SiAlON:Eu2+ with z =.64 and.37 mol% Eu2+. [ABSTRACT FROM AUTHOR]

We report the first synthesis of β‐SiAlON:Eu2+ phosphors from single‐source precursors, perhydropolysilazane (PHPS), chemically modified with Al(OCH(CH3)2)3, and EuCl2. The reactions occurring during the precursor synthesis and the subsequent thermal conversion of polymeric precursors into β‐SiAlON:Eu2+ phosphors have been studied by a complementary set of analytical techniques, including infrared spectroscopy, gas chromatography–mass spectrometry, thermogravimetry–mass spectrometry, X‐ray diffraction (XRD), photoluminescence spectroscopy, and scanning electron microscopy. It has been clearly established that Al(OCH(CH3)2)3 immediately reacted with PHPS to afford N–Al bonds at room temperature, whereas N–Eu bond formation was suggested to proceed above 600°C accompanied by the elimination of HCl up to 1000°C in flowing N2. The subsequent 1800°C‐heat treatment for 1 h under an N2 gas pressure at 980 kPa allowed converting the single‐source precursors into fine‐grained β‐SiAlON:Eu2+ phosphors. XRD analysis revealed that the Al/Si of.09 was the critical atomic ratio in the precursor synthesis to afford single‐phase β‐SiAlON (z =.55). Moreover, Eu2+‐doping was found to efficiently reduce the carbon impurity in the host β‐SiAlON. The polymer‐derived β‐SiAlON:Eu2+ phosphors exhibited green emission under excitation at 460 nm and achieved the highest green emission intensity at the critical dopant Eu2+ concentration at 1.48 at%. [ABSTRACT FROM AUTHOR]