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Color-center formation and thermal recovery in X-ray and electron-irradiated magnesium aluminate spinel
摘要： We have studied the formation of color centers in magnesium aluminate spinel (MgAl2O4) by X-ray and electron irradiations near room temperature (RT). For this purpose, Cu Kα radiation and three electron energies (1.0, 1.4, and 2.5 MeV) were used for variable fluences (up to 4.2 × 10^18 cm^?2). Off-line UV-visible absorption spectra were recorded at RT as well as at low temperature down to 27 K after electron irradiation. The dependence of the production rate of F centers (oxygen vacancies) on the electron energy yields a threshold displacement energy of 190 ± 10 eV for oxygen atoms at RT, which is much higher than the determinations by molecular-dynamics simulations. Such a discrepancy is discussed on the basis of available migration data of point defects in spinel. Equipartition of F0 and F+ centers, i.e., the neutral (VO^x) and singly ionized (VO^.) oxygen vacancies, is reached for high electron fluences. Moreover, the evolution of the width of color-center absorption bands versus temperature is interpreted with the classical theory for F centers (neutral halogen vacancies) in alkali halides. The Stokes shifts are deduced from the temperature dependence of the absorption bandwidths of color centers like for alkali halides and alkaline-earth oxides. Finally, isothermal annealing data for long annealing time show a non-zero asymptotic behavior for both F0 and F+ centers. This uncommon behavior is interpreted by charge exchange processes leading to an equilibrium state between those two color centers.
关键词： thermal recovery,X-ray irradiation,color centers,threshold displacement energy,F centers,electron irradiation,absorption spectroscopy,magnesium aluminate spinel
更新于2025-09-23 15:23:52
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Optical investigation of radiation-induced color centers in lithium fluoride thin films for low-energy proton-beam detectors
摘要： In the last few years, the peculiar photoluminescence properties of radiation-induced color centers in lithium fluoride (LiF) films have been successfully used for advanced diagnostics of low-energy proton beams produced by the TOP-IMPLART linear accelerator for protontheraphy under development at ENEA C.R. Frascati. The two-dimensional spatial dose map of the transversal section of proton beams was fully reconstructed in a wide interval of doses. In this work the optical emission properties of LiF thin films, grown by thermal evaporation on glass and Si (100) substrates and subsequently irradiated by proton beams of nominal energy 3 MeV at doses higher than 105 Gy, were carefully investigated. Their structural and morphological analyses were performed by X-ray diffraction and atomic force microscopy. A careful comparison of the photoluminescence and photoluminescence-excitation spectra of F2 and F3+ electronic defects was performed. Substrate-enhanced photoluminescence intensity increase up to 100% was observed in colored LiF films grown on Si substrates with respect to glass ones. This behavior can be substantially ascribed to the reflective properties of the Si substrate at the emission wavelengths of F2 and F3+ CCs, although other complex effects due to the polycrystalline nature of the films cannot be excluded.
关键词： Photoluminescence,Lithium fluoride,Radiation detectors,Color centers,Thin films
更新于2025-09-23 15:23:52
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The role of carbon in the formation mechanism of F-type centers in α-Al2O3:C,Mg single crystals
摘要： In this study, an α-Al2O3:C,Mg single crystal was grown using the Czochralski method with graphite resistance heating, Al2O3, MgO, and graphite powder as raw materials. Both the graphite heating unit and the shield served as the carbon source during the growth process. The structure and the optical properties of the crystal were investigated. The as-grown crystal shows a prominent absorption band at 206 nm, 230 nm, and 256 nm. The excitation-emission (EE) spectrum reveals a weak luminescence center (435/510 nm) that is attributed to the F2t (2 Mg). We calculate the concentration of the F-type centers using Smakula’s equation. Using the first principles simulation method, we studied the relation between the C atoms and the absorption properties of the crystal, and we discuss the role of carbon in the formation mechanism of the F-type luminescence centers for a α-Al2O3:C,Mg crystal.
关键词： Color centers,Al2O3:C,Crystals growth,Mg
更新于2025-09-23 15:22:29
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Effect of Uncontrollable Impurities on the Absorption Spectrum of a NaGd(WO4)2 Laser Crystal
摘要： Three NaGd(WO4)2 single crystals were grown by the Czochralski method using charges of different chemical purity. The impurity compositions of the grown crystals were analyzed by inductively coupled plasma mass spectrometry. The optical absorption spectra of the crystals were measured, and the effect of uncontrollable impurities on their optical properties and color was analyzed. The green color encountered in NaGd(WO4)2 crystals in some cases was shown to be due to the uncontrollable impurities of d elements, among which the chromium impurity had the most significant effect.
关键词： optical absorption,impurity purity,color centers,single crystals,zinc tungstate,ytterbium
更新于2025-09-23 15:21:01
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Fluorescent Nanodiamonds || Color Centers in Diamond
摘要： In this chapter, we will discuss the key features of nanodiamonds that are relevant to the development of fluorescent nanodiamonds (FNDs) and their many uses in biotechnology and beyond. Up till now, we have surveyed nanotechnology in previous chapters starting with its historical development and focusing, in particular, on the nanocarbon materials. With a general introduction to nanodiamonds (Chapter 2), we have learned some methods commonly used to prepare man‐made diamonds and the fundamental properties shared by all diamonds and nanodiamonds alike. In this and the following two chapters, we are about to find out that nanodiamonds can glow (Chapter 3), support (Chapter 4), and is safe to use (Chapter 5). These unique features have made nanodiamonds a superior material for a fast‐growing list of applications at present time and in the coming future.
关键词： biotechnology,fluorescent nanodiamonds,diamond,nanodiamonds,color centers
更新于2025-09-23 15:21:01
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Strongly inhomogeneous distribution of spectral properties of silicon-vacancy color centers in nanodiamonds
摘要： The silicon-vacancy (SiV) color center in diamond is a solid-state single photon emitter and spin quantum bit suited as a component in quantum devices. Here, we show that SiV centers in nanodiamonds exhibit a strongly inhomogeneous distribution with regard to the center wavelengths and linewidths of the zero-phonon-line (ZPL) emission at room temperature. We find that the SiV centers separate in two clusters: one group exhibits ZPLs with center wavelengths within a narrow range ≈730–742 nm and broad linewidths between 5 and 17 nm, whereas the second group comprises a very broad distribution of center wavelengths between 715 and 835 nm, but narrow linewidths from below 1 up to 4 nm. Supported by ab initio Kohn–Sham density functional theory calculations we show that the ZPL shifts of the first group are consistently explained by strain in the diamond lattice. Further, we suggest, that the second group showing the strongly inhomogeneous distribution of center wavelengths might be comprised of a new class of silicon-related defects. Whereas single photon emission is demonstrated for defect centers of both clusters, we show that emitters from different clusters show different spectroscopic features such as variations of the phonon sideband spectra and different blinking dynamics.
关键词： diamond,single photons,density functional theory calculations,color centers,optical emission,nanodiamond
更新于2025-09-19 17:15:36
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Multi-Qubit Registers of Individually Addressable Solid-State Defect Centers
摘要： Mesoscopic ensembles of qubits offer a platform for near-term applications in quantum technologies, as well as for studying many-body physics. Key in exploiting these systems is the ability to coherently control constituent qubits in a manner that leaves the quantum states of neighboring qubits unperturbed. Atom-like emitters in solids have emerged as a promising platform for computing, communications, and sensing. In particular, their long coherence times, coherent optical transitions, and the ability to couple to nearby long-lived nuclear spins make them excellent candidates for building medium-scale registers of coupled qubits. Here, we present progress towards producing and controlling such individually addressable ensembles. Our approach relies on the natural inhomogeneous distribution of optical transitions for solid-state color centers. This distribution allows us to excite individual centers even in tightly-grouped clusters. With this, we first demonstrate super-resolution localization and readout of individual nitrogen vacancy (NV) centers in diamond. We probe a system of three NV centers, demonstrating localization with a mean precision of 0.74 nm. While super-resolution imaging of NV centers has been achieved with other techniques, our approach uniquely allows for individual readout of single NVs in a cluster in a manner that maintains the states of nearby spins. We perform simultaneous control of two spin populations in a cluster of NVs, demonstrating preservation of coherence of one population during the optical readout of another. Lastly, we discuss recent work towards scalable creation of such clusters and techniques for producing systems of coupled spins with various defect centers.
关键词： spin-spin coupling,quantum technologies,super-resolution localization,qubits,solid-state color centers,nitrogen vacancy centers,many-body physics,atom-like emitters
更新于2025-09-16 10:30:52
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The Influence of X-ray and UV Laser Radiation on the Optical Properties of Alkali-Containing Silicate Glasses
摘要： The results of complex action of X-ray and nanosecond UV laser radiation on alkali-containing silicate glasses are presented. It is shown that X-ray irradiation of glasses forms luminescent color centers in them, which is related to increasing concentration of structural defects in glass network. Laser radiation destroys these defects, which is accompanied by bleaching of glasses and disappearance of luminescence in irradiated regions. The dynamics of glass bleaching under action of laser radiation and the influence of alkali-metal (Li, Na, K) ions on this process are studied. Mechanisms of destruction of color centers by laser radiation are proposed.
关键词： color centers,laser radiation,absorption,luminescence,silicate glass,X-ray radiation
更新于2025-09-16 10:30:52
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Large‐Scale Fabrication of Highly Emissive Nanodiamonds by Chemical Vapor Deposition with Controlled Doping by SiV and GeV Centers from a Solid Source
摘要： A new strategy to produce loose chemical vapor deposited nanodiamonds (ND) without the need of a seeded substrate, and that are intentionally doped by silicon vacancy and GeV centers from a solid source is presented. The addition of a low amount of gases such as N2 or O2 during growth is used as a control knob to finely tune the emission intensity of embedded color centers. NDs with a high brightness and a controllable amount of group IV color centers are eventually obtained. Their optical properties at low temperature indicate that this approach can usefully produce dispersed NDs that can deliver suitable optical performance for quantum technologies.
关键词： nanodiamond,color centers,quantum technologies,spectroscopy,chemical vapor deposition
更新于2025-09-12 10:27:22
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The Formation of Broadband Color Centers in PMMA by Femtosecond Laser Radiation
摘要： At present, organic materials modified by the laser irradiation are frequently used for the development and production of optical elements. Poly(methyl methacrylate) (PMMA) is one of the polymer materials which are most widely used in optics and optoelectronics. A broad transparency window and the ease of industrial processing are the main advantages of PMMA. Laser modification of PMMA allows creating color centers with radiation in a wide spectral range.
关键词： Poly(methyl methacrylate),color centers,laser modification
更新于2025-09-12 10:27:22