UV‐C emitting nanoscale scintillators can be used to sensitize cancer cells selectively against X‐rays during radiation therapy, due to the lethal DNA lesions caused by UV‐C photons. Unfortunately, nanoscale particles (NPs) show decreased UV‐C emission intensity. In this paper, the influence of different Nd3+ concentrations on the UV‐C emission of micro‐ and nanoscale LuPO4:Pr3+ is investigated upon X‐ray irradiation and vacuum UV excitation (160 nm). Co‐doped LuPO4 results in increased UV‐C emission independent of excitation source due to energy transfer from Nd3+ to Pr3+. The highest UV‐C emission intensity is observed for LuPO4:Pr3+,Nd3+(1%,2.5%) upon X‐ray irradiation. Finally, LuPO4 NPs co‐doped with different dopant concentrations are synthesized, and the biological efficacy of the combined approach (X‐rays and UV‐C) is assessed using the colony formation assay. Cell culture experiments confirm increased cell death compared to X‐rays alone due to the formation of UV‐specific DNA damages, supporting the feasibility of this approach. 相似文献
The rise of semiconductor‐based pump sources such as InxGa1‐xN‐laser diodes or frequency‐doubled optically pumped semiconductor lasers with emission wavelengths in the blue encourages a revisitation of the rare‐earth ions Pr3+, Sm3+, Tb3+, Dy3+, Ho3+ and Er3+ with respect to their properties as active ions in crystalline solid‐state laser materials with direct emission in the visible spectral range. Nowadays, some of these blue‐pumped visible lasers compete with Nd3+‐lasers in terms of efficiency and direct lasing at various colors from the cyan‐blue to the deep red can be addressed in very simple and compact laser setups. This paper highlights the spectroscopic properties of suitable rare‐earth ions for visible lasing and reviews the latest progress in the field of blue‐pumped visible rare‐earth doped solid‐state lasers.
Bursts of emissions of low‐energy electrons, including interatomic Coulomb decay electrons and Auger electrons (0–1000 eV), as well as X‐ray fluorescence produced by irradiation of large‐Z element nanoparticles by either X‐ray photons or high‐energy ion beams, is referred to as the nanoradiator effect. In therapeutic applications, this effect can damage pathological tissues that selectively take up the nanoparticles. Herein, a new nanoradiator dosimetry method is presented that uses probes for reactive oxygen species (ROS) incorporated into three‐dimensional gels, on which macrophages containing iron oxide nanoparticles (IONs) are attached. This method, together with site‐specific irradiation of the intracellular nanoparticles from a microbeam of polychromatic synchrotron X‐rays (5–14 keV), measures the range and distribution of OH radicals produced by X‐ray emission or superoxide anions () produced by low‐energy electrons. The measurements are based on confocal laser scanning of the fluorescence of the hydroxyl radical probe 2‐[6‐(4′‐amino)phenoxy‐3H‐xanthen‐3‐on‐9‐yl] benzoic acid (APF) or the superoxide probe hydroethidine‐dihydroethidium (DHE) that was oxidized by each ROS, enabling tracking of the radiation dose emitted by the nanoradiator. In the range 70 µm below the irradiated cell, radicals derived mostly from either incident X‐ray or X‐ray fluorescence of ION nanoradiators are distributed along the line of depth direction in ROS gel. In contrast, derived from secondary electron or low‐energy electron emission by ION nanoradiators are scattered over the ROS gel. ROS fluorescence due to the ION nanoradiators was observed continuously to a depth of 1.5 mm for both oxidized APF and oxidized DHE with relatively large intensity compared with the fluorescence caused by the ROS produced solely by incident primary X‐rays, which was limited to a depth of 600 µm, suggesting dose enhancement as well as more penetration by nanoradiators. In conclusion, the combined use of a synchrotron X‐ray microbeam‐irradiated three‐dimensional ROS gel and confocal laser scanning fluorescence microscopy provides a simple dosimetry method for track analysis of X‐ray photoelectric nanoradiator radiation, suggesting extensive cellular damage with dose‐enhancement beyond a single cell containing IONs. 相似文献
Semipolar (11\bar 2 \bar 2) ZnO was successfully grown on (112) LaAlO3/(LaAlO3)0.29(Sr2AlTaO6)0.35 substrate by pulsed laser deposition. The epitaxial relationship is [11\bar 23]_{\rm ZnO} // [11\bar 1]_{\rm LAO/LSAT} with the polar axis of [000\bar 1]_{\rm ZnO} pointing to the surface. For ZnO films with thickness of 1.6 μm, the threading dislocation density is ~1 × 109 cm–2, and the density of basal stacking faults is below 1 × 104 cm–1. The (11\bar 2 \bar 2) ZnO exhibits strong D0X emissions with a FWHM of 9 meV and very few green–yellow emissions in the low‐temperature (10 K) and room‐temperature photoluminescence spectra, respectively.
Fluorinated Eu‐doped SnO2 nanostructures with tunable morphology (shuttle‐like and ring‐like) are prepared by a hydrothermal method, using NaF as the morphology controlling agent. X‐ray diffraction, field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and energy dispersive spectroscopy are used to characterize their phase, shape, lattice structure, composition, and element distribution. The data suggest that Eu3+ ions are uniformly embedded into SnO2 nanocrystallites either through substitution of Sn4+ ions or through formation of Eu‐F bonds, allowing for high‐level Eu3+ doping. Photoluminescence features such as transition intensity ratios and Stark splitting indicate diverse localization of Eu3+ ions in the SnO2 nanoparticles, either in the crystalline lattice or in the grain boundaries. Due to formation of Eu‐F and Sn‐F bonds, the fluorinated surface of SnO2 nanocrystallites efficiently inhibits the hydroxyl quenching effect, which accounts for their improved photoluminescence intensity. 相似文献
Quaternary kesterite‐type Cu2ZnSnS4 (CZTS) nanoparticles (NPs) were successfully synthesized by a single‐step solvothermal process. Semiconductor CZTS nanoparticles were obtained from ethylene glycol (EG) and CZTS precursor after solvothermal process at 180 °C for 30 h in polyvinylpyrrolidone (PVP) medium. The synthesized CZTS NPs were further annealed at 450 °C in nitrogen atmosphere and used for further characterizations. The CZTS NPs were characterized using X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), micro Raman spectroscopy, high resolution transmission electron microscopy (HRTEM) and X‐ray photoelectron spectroscopy (XPS). The optical properties of the CZTS NPs were recorded by UV–vis absorption spectroscopy. The results showed that the synthesized CZTS nanoparticles are kesterite‐type CZTS, with good crystallinity and a stoichiometric composition. Moreover, the prepared nanoparticles have a size ranging from 5–7 nm and a band gap of ~1.5 eV.
Pr3+, Yb3+ co-doped Y2O3 transparent ceramics have been prepared by the solid state reaction and vacuum sintering. Down-conversion near infrared emission has been demonstrated upon a 482 nm excitation. The energy of the 482 nm blue photon was first absorbed by Pr3+ and then delivered to Yb3+. Possible energy transfer mechanisms from Pr3+ to Yb3+ have been discussed. Under the 482 nm excitation, the Pr4+-Yb2+ charge transfer state would not seriously influence the energy transfer process. The dominant one should be either the cooperative down-conversion or the two-step photon emission. The efficient down-conversion near infrared emission has potential application in enhancing the conversion efficiency of crystalline silicon solar cells. 相似文献
Resonant magnetic X-ray scattering was employed to investigate the magnetic state of epitaxial a* oriented thin films of the heavy fermion superconductor UNi2Al3. The observed incommensurate propagation vector as well as the Ne
l temperature correspond to
those of bulk samples. The 1200
film shows magnetic order with a correlation length >800 ? parallel to the growth axis. Out of the three possible magnetic
domains the one with the moment direction perpendicular to the film surface is not realized. 相似文献
Luminescent properties of Pr3+ or Mn2+ singly doped and Pr3+, Mn2+ co-doped LaMgB5O10 are investigated by synchrotron radiation VUV light. When LaMgB5O10:Pr3+ is excited at185 nm, the photon cascade emission between 4f levels of Pr3+ is observed. In the excitation spectra of LaMgB5O10:Mn2+ monitoring the 615 nm emission of Mn2+, several excitation bands in a spectral range from 330 to 580 nm are recorded, among which the most intense band is centered at 412 nm (6A1g→4Eg-4A1g). This band has considerable spectra overlap with the 410 nm emission (1S0→1I6) of Pr3+, which is favorable for energy transfer from Pr3+ to Mn2+. Such energy transfer is observed in the co-doped sample, converting the violet emission (410 nm) of Pr3+ into the red emission (615 nm) of Mn2+. The concentration dependence of transfer efficiency is also investigated. 相似文献
Pr3+, Mn2+ singly doped and co-doped LaMgB5O10 samples were prepared by solid-state reaction and their spectroscopic properties were investigated by synchrotron radiation VUV light. Significant spectra overlap between the Mn2+6A1g→(4Eg, 4A1g) excitation (centered at 412 nm) and the Pr3+1S0→(1I6, 3PJ) emission (410 nm) provided the possibility of energy transfer from Pr3+ to Mn2+. In the LaMgB5O10:Pr3+, Mn2+ samples investigated, the expected energy transfer process was observed as comparing the emission spectra of LaMgB5O10:Pr3+, Mn2+ samples with that of the LaMgB5O10:Mn2+. The shorter decay time of the 1S0→(1I6, 3PJ) transition in the co-doped samples was also an evidence of energy transfer from Pr3+ to Mn2+. By analyzing the energy transfer process, it was found that the energy transfer process in LaMgB5O10:Pr3+, Mn2+ was likely of resonant energy transfer and the re-absorption process can be excluded. The critical distances of energy transfer based on the electric dipole-dipole interaction and electric dipole-quadrupole interaction were calculated to be 4.78 and 9.46 Å in LaMgB5O10:Pr3+, Mn2+, respectively, which are smaller than the mean distance of Pr3+ and Mn2+ (17 Å) in the highest concentration-doped sample. The near neighboring PrMn clusters formed in the LaMgB5O10 host is responsible for the energy transfer process. 相似文献
A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e + e-annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e + e-and
spectral functions in the
channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and
, so that we refrain from averaging the two data sets. The values found for the lowest-order hadronic vacuum polarization contributions are
where the errors have been separated according to their sources: experimental, missing radiative corrections in e + e-data, and isospin breaking. The corresponding Standard Model predictions for the muon magnetic anomaly read
where the errors account for the hadronic, light-by-light (LBL) scattering and electroweak contributions. The deviations from the measurement at BNL are found to be
(1.9
) and
(0.7
) for the e + e-- and
-based estimates, respectively, where the second error is from the LBL contribution and the third one from the BNL measurement.Received: 7 September 2003, Published online: 30 October 2003 相似文献
Fluorescence lifetimes of formaldehyde excited at 352 nm (
A2 –
A1 401 band) were measured as a function of bath gas pressure. He, N2, O2, CO2 and HCHO were investigated for the bath gas and the temperature dependence between 298 and 500 K for N2 and O2 bath gases was also examined. It was found that the non-linear pressure dependence of the lifetime is successfully reproduced by the model formula
where [M] is the concentration of a bath gas and kf, kq, ka, kb and kp are the constants determined for each bath gas. This model assumes that the optically excited formaldehyde undergoes a reversible collision transfer to a state of higher spontaneous decay rate along with direct collisional and spontaneous deactivation pathways. It was confirmed that a lifetime in a bath gas mixture can be reproduced by this formula with the constants individually obtained as linear combinations of each bath gas contribution. The temperature dependence is expressed by assigning activation energies for the constants in the formula. 相似文献