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Distributions of Eu2+ and Eu3+ do affect the optical properties. However, the substitution of the activator ions hardly perturbed the crystal structure of the host lattice. Without the differences in crystal structure, it is not trivial to develop an effective descriptor to investigate stoichiometry-dependent mechanism to explore the effects of Eu species on valence states. In this study, through x-ray nanodiffraction, x-ray fluorescence, x-ray absorption near edge structure, and x-ray excited optical luminescence, we mapped the valence state distributions of Eu species to calculate the local mixing enthalpy and entropy. The calculated thermodynamics parameters show good agreement with the optical properties. We found that Eu2+ of Eu-doped BaAl2O4 predominantly existed in a divalent state, which results in segregation phenomena of local Eu2+ and Eu3+ ions. [ABSTRACT FROM AUTHOR]

Distributions of Eu2+ and Eu3+ do affect the optical properties. However, the substitution of the activator ions hardly perturbed the crystal structure of the host lattice. Without the differences in crystal structure, it is not trivial to develop an effective descriptor to investigate stoichiometry-dependent mechanism to explore the effects of Eu species on valence states. In this study, through x-ray nanodiffraction, x-ray fluorescence, x-ray absorption near edge structure, and x-ray excited optical luminescence, we mapped the valence state distributions of Eu species to calculate the local mixing enthalpy and entropy. The calculated thermodynamics parameters show good agreement with the optical properties. We found that Eu2+ of Eu-doped BaAl2O4 predominantly existed in a divalent state, which results in segregation phenomena of local Eu2+ and Eu3+ ions. [ABSTRACT FROM AUTHOR]

Persistent luminescence (PersL) is an optical phenomenon which allows for materials to emit luminescence after ceasing excitation. The long‐lasting luminescence is ascribed to the presence of trap states, which can be exploited through the introduction of various dopants and post‐synthesis treatment. In this study, ZnGa2O4 : Cr3+ (CZGO), one of the most widely investigated near‐infrared‐emitting PersL materials, is synthesized in the form of nanoparticles, and incorporated into amorphous calcium phosphate (ACP) to form a luminescent nanocomposite with drug attachment potential. The effects of annealing CZGO in the composite are comparatively studied alongside the composite that contains unannealed CZGO. We find that ACP with annealed CZGO exhibits much higher luminescence intensity and longer PersL duration. The formation of the nanocomposite also results in the redistribution of Zn, and its influence on the composite luminescence intensity and the long‐term chemical stability are investigated. [ABSTRACT FROM AUTHOR]

The soft and polar nature of quasi‐2D (PEA)2PbBr4 perovskite, and robust photo‐generated excitons lead exciton‐polaritons and exciton‐polarons as the important phenomena near the band edge for application in the lighting aspect. In this work, a convenient methodology is proposed based on the polariton resonant modes in temperature‐dependent (77 K to RT) spectroscopy, and investigate the effect of these quasi‐particles on refractive index dispersion. The large binding energy (≈335 meV) of quasi‐2D excitons is obtained by the reflectance measurements at 77 K. Stable exciton‐polaritons and exciton‐polarons are confirmed by energy dispersions and the observation of self‐trapped exciton‐polaron state, respectively. Furthermore, the large negative thermal‐optic coefficient due to damping effect of exciton‐phonon scattering is observed. The phenomenon is opposite to those observed in conventional semiconductors (e.g., Si, Ge, GaN, AlN, GaAs, AlAs, and ZnO etc.). The observed stable negative thermal‐optic coefficients from 160 K to RT indicate that the quasi‐2D perovskite can be used as a phase compensator for conventional semiconductor materials. [ABSTRACT FROM AUTHOR]

The cadmium tungstate rods have been given much attention due to their potential for usage in numerous luminescent applications. We have prepared single crystalline Sn-doped Cd1−xSnxWO4 (where x = 0, 1, 3, and 5%) nanorods (NRDs) and characterized them using refined X-ray diffraction and TEM analysis, revealing a monoclinic phase and a crystallite size that decreased from 62 to 38 nm as Sn concentration increased. Precise Sn doping modulation in CdWO4 NRDs causes surface recombination of electrons and holes, which causes the PL intensity to decrease as the Sn content rises. The chromaticity diagram shows that an increase in the Sn content caused a change in the emission color from sky blue to light green, which was attributed to the increased defect density. The photoluminescence time decay curve of all samples fit well with double-order exponential decay, and the average decay lifetime was found to be 1.11, 0.93, and 1.16 ns for Cd1−xSnxWO4, x = 0, 1, and 5%, respectively. This work provides an understanding of the behavior of Sn-doped CdWO4 NRDs during electron transitions and the physical nature of emission that could be used in bio-imaging, light sources, displays, and other applications. [ABSTRACT FROM AUTHOR]

Monoclinic CdWO4 is a member of the tungstate family with great potential in diverse applications. However, CdWO4 exhibits a diamagnetic property with a wideband gap of 3.7 eV, limiting its widespread applications. This study reports significant modulation of magnetic and optical properties of hydrothermally grown single-crystalline CdWO4 nanorods with controllable substitution of Cu2+ ions at the Cd2+ site. The chemical environment of Cu and the magnetic and luminescence of nanorods were thoroughly investigated using synchrotron-based powder X-ray diffraction, temperature-dependent photoluminescence, X-ray absorption, element selective X-ray excited optical luminescence spectroscopies, a magnetometer, and micro-Raman spectroscopy. The main feature of this study is an astonishing redshift of ∼0.8 eV in the bandgap energy accompanied by a relative ∼46% drop in the internal quantum efficiency and a progressive transition from diamagnetic to an enhanced magnetization concerning the Cu content. The experimental findings show that significant modulation in optical and magnetic properties is correlated with Cu-doping-induced intermediate energy states and [CuO6] ferromagnetic clusters. The outcome of this study provides important insight into designing doped nanomaterials for photocatalytic applications. [ABSTRACT FROM AUTHOR]

This study develops and successfully demonstrates visualization methods for the characterization of europium (Eu)‐doped BaAl2O4 phosphors using X‐ray nanoprobe techniques. X‐ray fluorescence (XRF) mapping not only gives information on the elemental distributions but also clearly reveals the valence state distributions of the Eu2+ and Eu3+ ions. The accuracy of the estimated valence state distributions was examined by performing X‐ray absorption spectroscopy (XAS) across the Eu L3‐edge (6.977 keV). The X‐ray excited optical luminescence (XEOL) spectra exhibit different emission lines in the selected local areas. Their corresponding emission distributions can be obtained via XEOL mapping. The emission properties can be understood through correlation analysis. The results demonstrate that the main contribution to the luminescence intensity of the Eu‐doped BaAl2O4 comes from the Eu2+ activator and the emission intensity will not be influenced by the concentration of Eu2+ or Eu3+ ions. It is anticipated that X‐ray nanoprobes will open new avenues with significant characterization ability for unravelling the emission mechanisms of phosphor materials. [ABSTRACT FROM AUTHOR]