Color-tunable visible photoluminescence of Eu:CaF2 single crystals: variations of valence state and local lattice environment of Eu ions

Mineral Nanomedicine to Enhance the Efficacy of Adjuvant Radiotherapy for Treating Osteosarcoma

It is vital to remove residual tumor cells after resection to avoid the recurrence and metastasis of osteosarcoma. In this study, a mineral nanomedicine, europium-doped calcium fluoride (CaF₂:Eu) nanoparticles (NPs), is developed to enhance the efficacy of adjuvant radiotherapy (i.e., surgical resection followed by radiotherapy) for tumor cell growth and metastasis of osteosarcoma. In vitro studies show that CaF₂:Eu NPs (200 μg/mL) exert osteosarcoma cell (143B)-selective toxicity and migration-inhibiting effects at a Eu dopant amount of 2.95 atomic weight percentage. These effects are further enhanced under X-ray irradiation (6 MeV, 4 Gy). Furthermore, in vivo tests show that intraosseous injection of CaF₂:Eu NPs and X-ray irradiation have satisfactory therapeutic efficacy in controlling primary tumor size and inhibiting primary tumor metastasis. Overall, our results suggest that CaF₂:Eu NPs with their osteosarcoma cell (143B)-selective toxicity and migration-inhibiting effects combined with radiotherapy might be nanomedicines for treating osteosarcoma after tumor resection.

Highly Resolved and Robust Dynamic X-Ray Imaging Using Perovskite Glass-Ceramic Scintillator with Reduced Light Scattering

All-inorganic perovskite quantum dots (QDs) CsPbX3 (X = Cl, Br, and I) have recently emerged as a new promising class of X-ray scintillators. However, the instability of perovskite QDs and the strong optical scattering of the thick opaque QD scintillator film imped it to realize high-quality and robust X-ray image. Herein, the europium (Eu) doped CsPbBr3 QDs are in situ grown inside transparent amorphous matrix to form glass-ceramic (GC) scintillator with glass phase serving as both matrix and encapsulation for the perovskite QD scintillators. The small amount of Eu dopant optimizes the crystallization of CsPbBr3 QDs and makes their distribution more uniform in the glass matrix, which can significantly reduce the light scattering and also enhance the photoluminescence emission of CsPbBr3 QDs. As a result, a remarkably high spatial resolution of 15.0 lp mm-1 is realized thanks to the reduced light scattering, which is so far a record resolution for perovskite scintillator based X-ray imaging, and the scintillation stability is also significantly improved compared to the bare perovskite QD scintillators. Those results provide an effective platform particularly for the emerging perovskite nanocrystal scintillators to reduce light scattering and improve radiation hardness.

Influence of Eu3+ on the Structure and Photophysical Properties in (Y,Gd)F3 Nanophosphors

The scientific community has shown a growing interest in relating to the lanthanide based luminescent materials and it has made an effort to develop them. Among these several luminescent materials, we have proposed to developed (Y,Gd)F₃ nanophosphors doped with distinct of Eu³⁺ concentrations using modified hydrothermal process. The effect of co-doping of rare earth activators to the host lattice structure and morphology are investigated using different analytical techniques. The diffuse reflectance spectra reveal a tuning of optical band gap due to substitutions. From the extensive XPS analysis, Gd and Eu are found to be in a stable ionic state of +3 which is replacing Y³⁺ in YF₃ host. Photoluminescence emission spectra of the nanophosphors are excited by near ultraviolet (UV, 393 nm) excitation. From photoluminescence study, the intensity variation is observed for emission peak at 591 nm and fluorescence quenching occurs at higher doping level. This effect subsequently explained on the frame work of local symmetry and nonradiative transfer among multipole-multipole interaction. At 393 nm excitation Eu³⁺ (2, 3, 5, 7, 10 at %) doped (Y, Gd) F₃ show CIE chromaticity coordinates shifted to red regions with increase in Eu doping levels. Because of the longer decay time these phosphors can be used for bio-labeling and other similar applications.

Tailoring local coordination structure of the Er3+ ions for tuning the up-conversion multicolor luminescence

The regulation of the local structure around Er³⁺ ions is an important channel for adjusting the characteristic of up-conversion luminescence. In this paper, the cubic-phased Er³⁺:CaF₂ crystals with different Er³⁺ doping concentrations were fabricated with temperature gradient technique (TGT) method and the effect of the local coordination structure of the Er³⁺ ions on its luminescence performance was investigated. The local coordination structure of Er³⁺ ions was simulated by density functional theory. The computational results show that clusters evolve from low order to high order with the increase of Er³⁺ ion doping concentration. In this evolution process, the local structure transforms from cubic structure to the co-existence of cubic and lower symmetric square anti-prism structures. Meanwhile, the distance between Er³⁺ ions in the cluster decreased first and then increased slightly, and in dimers and trimers this distance reached the minimum. Under 980 nm excitation, with the increase of Er³⁺ ion concentration, the intensity ratios of the red and green emissions of Er³⁺:CaF₂ first increased from 0.61 to 42.03 and then decreased to 12.11. The corresponding up-conversion luminescence gamut was adjusted from monochrome green to red to red-yellow. This work provides a new thread for realizing upconversion multicolor luminescence by regulating the clusters of rare earth ions.

Absolute Luminescence Efficiency of Europium-Doped Calcium Fluoride (CaF2:Eu) Single Crystals under X-ray Excitation

The absolute luminescence efficiency (AE) of a calcium fluoride (CaF2:Eu) single crystal doped with europium was studied using X-ray energies met in general radiography. A CaF2:Eu single crystal with dimensions of 10 × 10 × 10 mm3 was irradiated by X-rays. The emission light photon intensity of the CaF2:Eu sample was evaluated by measuring AE within the X-ray range from 50 to 130 kV. The results of this work were compared with data obtained under similar conditions for the commercially employed medical imaging modalities, Bi4Ge3O12 and Lu2SiO5:Ce single crystals. The compatibility of the light emitted by the CaF2:Eu crystal, with the sensitivity of optical sensors, was also examined. The AE of the 10 × 10 × 10 mm3 CaF2:Eu crystal peaked in the range from 70 to 90 kV (22.22 efficiency units; E.U). The light emitted from CaF2:Eu is compatible with photocathodes, charge coupled devices (CCD), and silicon photomultipliers, which are used as radiation sensors in medical imaging systems. Considering the AE results in the examined energies, as well as the spectral compatibility with various photodetectors, a CaF2:Eu single crystal could be considered for radiographic applications, including the detection of charged particles and soft gamma rays.