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Temperature sensing at the nanoscale is a significant experimental challenge. Here, an approach using dressed states is reported to make a leading quantum sensor – the nitrogen‐vacancy (NV) center in diamond – selectively sensitive to temperature, even in the presence of normally confounding magnetic fields. Using an experimentally straightforward approach, the magnetic sensitivity of the NV center is suppressed by a factor of seven, while retaining full temperature sensitivity and narrowing the NV center linewidth. These results demonstrate the power of engineering the sensor Hamiltonian using external control fields to enable sensing with improved specificity to target signals. [ABSTRACT FROM AUTHOR]

Calcium aluminate (CA)‐based glasses have drawn significant attention owing to their pronounced optical, mechanical, and chemical properties for potential applications in IR photonics. Nonetheless, limitations related to their poor glass‐forming ability was addressed by incorporating ZnO that has formed negatively charged [ZnO4]2− and [AlO4]− units, thereby generating the oxygen‐excess defects. These defects impart a detrimental effect on the optical properties. Thus, the present study explores the impact of Li2O, Na2O, K2O, and GeO2 inclusion in the barium–zinc–calcium–aluminate (BZCA) glass to eliminate the oxygen‐excess defects. The molecular structure of the glass matrix was examined by Raman, NMR, and XPS along with the bulk diffusivity of the glasses through MD simulation and are correlated to elucidate the origin of the defect centers. Due to higher diffusivity, Li+ and Na+ cations decrease Al–O hole centers (Al–OHC) and O3−${\mathrm{O}}_3^ - $ defects but promote F+ (Farbe) centers while K+ ions having lower diffusivity and enhance the O3−${\mathrm{O}}_3^ - $ defects. Interestingly, all the defect centers are substantially reduced in GeO2‐containing glasses. Further, multivalent Cr ions are doped to optically probe the defect centers through UV–Vis–NIR absorption and photoluminescence spectra. Cr3+ and Cr4+ are found dominant in Li+‐and Na+‐containing glasses due to the presence of less O3−${\mathrm{O}}_3^ - $ defect, whereas excess O3−${\mathrm{O}}_3^ - $ converts all Cr3+ into Cr6+ for K+‐containing glasses. Additionally, broadband NIR emission from Cr4+ can functionalize selective glasses for laser and telecommunication applications. [ABSTRACT FROM AUTHOR]

Diamond containing nitrogen‐vacancy centers (NV−) is one of the most investigated materials for quantum technologies, because of this system's exceptional spin properties. Although the NV− optical transition is very bright, it suffers from spectral diffusion and weak zero‐phonon line, and is in the visible range. This limits integration into quantum photonic structures and interfacing with optical fiber networks. In contrast, rare earth (RE) ions exhibit extremely narrow and stable optical transitions, including erbium's 1.5 µm telecom wavelength. Combining RE with NV− properties through short‐range interactions is however challenging as RE do not readily enter the diamond lattice. In this work, a thin‐film‐based architecture in which RE and NV− centers can interact while preserving their unique properties is introduced. Thin films of Er3+:Y2O3 are grown by chemical vapor deposition on diamond substrates with well‐crystallized and highly textured structures. An extensive spectroscopic study of Er3+ transitions at room and low temperatures further reveals that photoluminescence spectra and decays are close to bulk materials. It is also shown that Y2O3 thin film deposition has no detrimental effects on NV− optical and spin properties. RE thin films deposited on diamond can thus be suitable for building hybrid materials for new functionalities in quantum sensing, communication, and processing. [ABSTRACT FROM AUTHOR]

Fused Filament Fabrication is a promising manufacturing technology for the circularity of space missions. Potential scenarios include in‐orbit applications to maximize mission life and to support long‐term exploration missions with in situ manufacturing and recycling. However, its adoption is restricted by the availability of engineering polymers displaying mechanical performance combined with resistance to space conditions. Here, a thermotropic Liquid Crystal Polymer (LCP) is reported as a candidate material with extrusion 3D printing. To expand its scope of applicability to structural parts for space applications, four different exposure conditions are studied: thermal cycling under vacuum, atomic oxygen, UV, and electron irradiations. While 1 MeV‐electron irradiation leads to a green coloration due to annealable color centers, the mechanical performance is only slightly decreased in dynamic mode. It is also found that increased printing temperature improves transverse strength and resistance to thermal cycling with the trade‐off of tensile stiffness and strength. Samples exposed to thermal cycling and the highest irradiation dose at lower printing temperatures still display a Young's modulus of 30 GPa and 503 MPa of tensile strength which is exceptionally high for a 3D‐printed polymer. For the types of exposure studied, overall, the results indicate that LCP 3D‐printed parts are well suited for space applications. [ABSTRACT FROM AUTHOR]

Uneven micron-sized pores on the surface of the polycrystalline alumina (Al 2 O 3) substrates can affect their performance as electrical insulating plates. In this study, we investigated the sealing of these pores with amorphous Al 2 O 3 films deposited via atmospheric chemical vapor deposition. Furthermore, we conducted annealing treatments on the samples. The color change of the deposited Al 2 O 3 films was investigated using the Commission Internationale de I'Eclairage color space. Notably, the deposited films initially changed the sample color from white to orange or brown. However, increasing the annealing temperature and duration reversed this discoloration effectively and restored the original white (colorless) appearance of the sample. We measured thermal conductivity using the flame flash method with the H 2 -O 2 flame to assess the influence of sealing. While the unsealed substrate exhibited a thermal conductivity of 4.66 W/mK in the range of 400–500 °C, the annealed and flattened Al 2 O 3 film deposited on the substrate maintained a comparable thermal conductivity of 4.67 W/mK within the same temperature range. This finding demonstrates that our sealing method successfully filled the pores while having minimal influence on thermal conductivity, which is a crucial property for electrical insulation applications. [ABSTRACT FROM AUTHOR]

The distinct spin, optical, and coherence characteristics of solid-state spin defects in semiconductors have positioned them as potential qubits for quantum technologies. Both bulk and two-dimensional materials, with varying structural properties, can serve as crystalline hosts for color centers. In this study, we conduct a comparative analysis of the spin–optical, electron–nuclear, and relaxation properties of nitrogen-bound vacancy defects using electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR) techniques. We examine key parameters of the spin Hamiltonian for the nitrogen vacancy (NV−) center in 4H-SiC: D = 1.3 GHz, Azz = 1.1 MHz, and CQ = 2.53 MHz, as well as for the boron vacancy (VB−) in hBN: D = 3.6 GHz, Azz = 85 MHz, and CQ = 2.11 MHz, and their dependence on the material matrix. The spin–spin relaxation times T2 (NV− center: 50 µs and VB−: 15 µs) are influenced by the local nuclear environment and spin diffusion while Rabi oscillation damping times depend on crystal size and the spatial distribution of microwave excitation. The ENDOR absorption width varies significantly among color centers due to differences in crystal structures. These findings underscore the importance of selecting an appropriate material platform for developing quantum registers based on high-spin color centers in quantum information systems.

There is an urgent need to increase the global data storage capacity, as current approaches lag behind the exponential growth of data generation driven by the Internet, social media, and cloud technologies. In addition to increasing storage density, new solutions should provide long‐term data archiving that goes far beyond traditional magnetic memory, optical disks, and solid‐state drives. Here, a concept of energy‐efficient, ultralong, high‐density data archiving is proposed, based on optically active atomic‐size defects in a radiation resistance material, silicon carbide (SiC). The information is written in these defects by focused ion beams and read using photoluminescence or cathodoluminescence. The temperature‐dependent deactivation of these defects suggests a retention time minimum over a few generations under ambient conditions. With near‐infrared laser excitation, grayscale encoding and multi‐layer data storage, the areal density corresponds to that of Blu‐ray discs. Furthermore, it is demonstrated that the areal density limitation of conventional optical data storage media due to the light diffraction can be overcome by focused electron‐beam excitation. [ABSTRACT FROM AUTHOR]

High-spin defects (color centers) in wide-gap semiconductors are considered as a basis for the implementation of quantum technologies due to the unique combination of their spin, optical, charge, and coherent properties. A silicon carbide (SiC) crystal can act as a matrix for a wide variety of optically active vacancy-type defects, which manifest themselves as single-photon sources or spin qubits. Among the defects, the nitrogen-vacancy centers (NV) are of particular importance. This paper is devoted to the application of the photoinduced electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR) techniques at a high-frequency range (94 GHz) to obtain unique information about the nature and properties of NV defects in SiC crystal of the hexagonal 4H and 6H polytypes. Selective excitation by microwave and radio frequency pulses makes it possible to determine the microscopic structure of the color center, the zero-field splitting constant (D = 1.2–1.3 GHz), the phase coherence time (T2 ), and the values of hyperfine (≈1.1 MHz) and quadrupole (Cq ≈ 2.45 MHz) interactions and to define the isotropic (a = −1.2 MHz) and anisotropic (b = 10–20 kHz) contributions of the electron–nuclear interaction. The obtained data are essential for the implementation of the NV defects in SiC as quantum registers, enabling the optical initialization of the electron spin to establish spin–photon interfaces. Moreover, the combination of optical, microwave, and radio frequency resonant effects on spin centers within a SiC crystal shows the potential for employing pulse EPR and ENDOR sequences to implement protocols for quantum computing algorithms and gates. [ABSTRACT FROM AUTHOR]

This study presents theoretical and experimental investigations into the electron and hole color centers in BaFBr crystals, characterizing their electronic and optical properties. Stoichiometric BaFBr crystals grown by the Steber method were used in the experiments. Radiation defects in BaFBr crystals were created by irradiation with 147 MeV 84Kr ions with up to fluences of 1010–1014 ions/cm2. The formation of electron color centers (F(F−), F2(F−), F2(Br−)) and hole aggregates was experimentally established by optical absorption spectroscopy. Performed measurements are compared with theoretical calculations. It allows us to determine the electron transition mechanisms and investigate the processes involved in photoluminescence emission in Eu-doped BaFBr materials to enhance the understanding of the fundamental electronic structure and properties of electron and hole color centers formed in BaFBr crystals. [ABSTRACT FROM AUTHOR]

The distinct spin, optical, and coherence characteristics of solid-state spin defects in semiconductors have positioned them as potential qubits for quantum technologies. Both bulk and two-dimensional materials, with varying structural properties, can serve as crystalline hosts for color centers. In this study, we conduct a comparative analysis of the spin–optical, electron–nuclear, and relaxation properties of nitrogen-bound vacancy defects using electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR) techniques. We examine key parameters of the spin Hamiltonian for the nitrogen vacancy ( N V − ) center in 4H-SiC: D = 1.3 GHz, Azz = 1.1 MHz, and CQ = 2.53 MHz, as well as for the boron vacancy ( V B − ) in hBN: D = 3.6 GHz, Azz = 85 MHz, and CQ = 2.11 MHz, and their dependence on the material matrix. The spin–spin relaxation times T2 ( N V − center: 50 µs and V B − : 15 µs) are influenced by the local nuclear environment and spin diffusion while Rabi oscillation damping times depend on crystal size and the spatial distribution of microwave excitation. The ENDOR absorption width varies significantly among color centers due to differences in crystal structures. These findings underscore the importance of selecting an appropriate material platform for developing quantum registers based on high-spin color centers in quantum information systems. [ABSTRACT FROM AUTHOR]

The chemical vapor deposition (CVD) of diamond allows the controllable formation of the material with desirable structure and elemental composition. In this study, Ge-doped microcrystalline and nanocrystalline diamond (NCD) films are synthesized using microwave plasma-assisted CVD in CH4-H2-GeH4-N2 gas mixtures. We grow series of 2 μm thick NCD films with variations in gas composition [N2] = 0 − 4% and [CH4] = 10 − 15%. We investigate and compare the structure, phase composition, and luminescent characteristics of the grown films. The luminescent signals from Silicon vacancy (SiV, 738 nm) and Germanium vacancy (GeV, 602 nm) color centers in diamond are registered. The additional annealing of the as-grown films in air is used to remove the excessive sp2 phase that hinders their luminescent properties. For both SiV and GeV centers, we find conditions for CVD growth of NCD films that are as bright or even brighter than Si-doped and Ge-doped high-quality microcrystalline diamond films (MCD) grown without N2 additions. These results may be used for the fabrication of NCD films and plates with high concentrations of SiV and GeV centers, which may serve as source material for the fabrication of sub-micrometer-sized luminescent diamond particles for local optical thermometry. [ABSTRACT FROM AUTHOR]

Schottky barriers on GaN is considered on the basis of an analysis of the features of the current-voltage characteristics of Ni/n-GaN diodes. It is found that the forward I–V characteristics on a semilogarithmic scale have the form of curves with steps at biases corresponding to the Gaussian bands of localized states of defects in the GaN band gap. It is shown that the experimental current–voltage characteristics are in agreement with a simple physical model that takes into account the thinning of the Schottky barrier due to the space charge of ionized deep centers, which stimulates the concentration of the electric field near the Schottky contact and tunneling of electrons by hopping between local centers through the near-contact layer. At forward biases, this causes an exponential increase in the tunneling current of electrons thermally activated to an energy corresponding to the peak of the Gaussian band. The recharging of the states of the Gaussian band is accompanied by a decrease in the probability of tunneling and the appearance of a current plateau on the forward log I(Vj) curves. An increase in the space charge of deep centers under reverse bias leads to tunneling leakage and limits the breakdown voltage. [ABSTRACT FROM AUTHOR]

The multilevel encoding (MLE) scheme is an effective method for improving the anticounterfeiting encryption capabilities of physically unclonable functions (PUFs). However, owing to the correlation between encoding layers, the encoding capacity (EC) is difficult to improve by orders of magnitude. Herein, four noncorrelated structures in the diamond crystal structure (carbon–carbon single bond, defect luminescence structures, spin structures, and electron energy distribution structures) are considered for MLE. First, the microdiamonds containing nitrogen‐vacancy (NV) color centers are embedded into polydimethylsiloxane (PDMS) to fabricate PUFs. Using an optical imaging system, four codable images of four noncorrelated structures are read. The noncorrelation of the four‐level encoding structure is verified by calculating the Hamming distance (0.496 ± 0.02). The results show that EC exponentially improves to 24×10 000/(100 pixels)2. Furthermore, the encoding method based on the energy level does not depend on physical structure parameters, such as the size and position of the spin structure. Thus, it is protected from structural modeling attacks, resulting in high security. Moreover, PUF labels based on PDMS flexible substrates can be employed for various flexible applications. In the proposed scheme, the information is encrypted by a four‐level two‐dimensional (2D) barcode and decoded by self‐developed PUF authentication software. The proposed scheme presents a way for developing next‐generation PUFs with super‐high EC. [ABSTRACT FROM AUTHOR]

The paper introduces a method for representing data on the local atomic structure as histograms of pair radial distribution functions categorized by atom types. This method is used to construct a structure descriptor essential for determining the material structure using machine learning and artificial intelligence methods. A distinctive feature of the approach is the simultaneous use of two sets of pair radial distribution functions: for pairs of all atom types and for pairs involving a selected absorbing atom. The developed approach is tested for determining the nearest environment of silver atoms in color centers in sodium-silicate glasses based on the spectra of X-ray absorption near the absorption edge of Ag. The informativeness of the proposed structure descriptor is demonstrated by its ability to recreate a three-dimensional model of the silver color center's structure from the corresponding pair distance histograms. Using multiple machine-learning methods, we demonstrate that the proposed descriptor enables the high-quality reproduction of X-ray absorption near edge structure (XANES) spectra for color centers in glass within the framework of the finite-difference method, which results in a four-order-of-magnitude cut in the calculation time for the XANES spectra. The constructed machine-learning model establishes a fundamental connection between the atomic structure of color centers in glasses and the silver XANES spectrum, which is essential for determining the structure of glasses. [ABSTRACT FROM AUTHOR]

Quantum processors based on color centers in diamond are promising candidates for future large-scale quantum computers thanks to their flexible optical interface, (relatively) high operating temperature, and high-fidelity operation. Similar to other quantum computing platforms, the electrical interface required to control and read out such qubits may limit both the performance of the whole system and its scalability. To address this challenge, this work analyzes the requirements of the electrical interface and investigates how to efficiently implement the electronic controller in a scalable architecture comprising a large number of identical unit cells. Among the different discussed functionalities, a specific focus is devoted to the generation of the static and dynamic magnetic fields driving the electron and nuclear spins, because of their major impact on fidelity and scalability. Following the derived requirements, different system architectures, such as a qubit frequency-multiplexing scheme, are considered to identify the most power efficient approach, especially in the presence of inhomogeneity of the qubit Larmor frequency across the processor. As a result, a non-frequency-multiplexed 1-$\,\mathrm{m}\mathrm{m}^{2}$ unit-cell architecture is proposed as the optimal solution, able to address up to one electron-spin qubit and nine nuclear-spin qubits within a 3-mW average power consumption, thus establishing the baseline for the scalable electrical interface for future large-scale color-center quantum computers.

Short-pulse ion beams have been developed in recent years and now enable applications in materials science. A tunable flux of selected ions delivered in pulses of a few nanoseconds can affect the balance of defect formation and dynamic annealing in materials. We report results from color center formation in silicon with pulses of 900 keV protons. G-centers in silicon are near-infrared photon emitters with emerging applications as single-photon sources and for spin-photon qubit integration. G-centers consist of a pair of substitutional carbon atoms and one silicon interstitial atom and are often formed by carbon ion implantation and thermal annealing. Here, we report on G-center formation with proton pulses in silicon samples that already contained carbon, without carbon ion implantation or thermal annealing. The number of G-centers formed per proton increased when we increased the pulse intensity from 6.9 × 109 to 7.9 × 1010 protons/cm2/pulse, demonstrating a flux effect on G-center formation efficiency. We observe a G-center ensemble linewidth of 0.1 nm (full width half maximum), narrower than previously reported. Pulsed ion beams can extend the parameter range available for fundamental studies of radiation-induced defects and the formation of color centers for spin-photon qubit applications.

Color centers in diamond are one of the most promising tools for quantum information science. Of particular interest is the use of single-crystal diamond membranes with nanoscale-thickness as hosts for color centers. Indeed, such structures guarantee a better integration with a variety of other quantum materials or devices, which can aid the development of diamond-based quantum technologies, from nanophotonics to quantum sensing. A common approach for membrane production is what is known as “smart-cut”, a process where membranes are exfoliated from a diamond substrate after the creation of a thin sub-surface amorphous carbon layer by He+ implantation. Due to the high ion fluence required, this process can be time-consuming. In this work, we demonstrated the production of thin diamond membranes by neon implantation of diamond substrates. With the target of obtaining membranes of ∼200 nm thickness and finding the critical damage threshold, we implanted different diamonds with 300 keV Ne+ ions at different fluences. We characterized the structural properties of the implanted diamonds and the resulting membranes through SEM, Raman spectroscopy, and photoluminescence spectroscopy. We also found that a SRIM model based on a two-layer diamond/sp2-carbon target better describes ion implantation, allowing us to estimate the diamond critical damage threshold for Ne+ implantation. Compared to He+ smart-cut, the use of a heavier ion like Ne+ results in a ten-fold decrease in the ion fluence required to obtain diamond membranes and allows to obtain shallower smart-cuts, i.e. thinner membranes, at the same ion energy.

High-performance optical quantum memories serving as quantum nodes are crucial for the distribution of remote entanglement and the construction of large-scale quantum networks. Notably, quantum systems based on single emitters can achieve deterministic spin–photon entanglement, which greatly simplifies the difficulty of constructing quantum network nodes. Among them, optically interfaced spins embedded in solid-state systems, as atomic-like emitters, are important candidate systems for implementing long-lived quantum memory due to their stable physical properties and robustness to decoherence in scalable and compact hardware. To enhance the strength of light-matter interactions, optical microcavities can be exploited as an important tool to generate high-quality spin–photon entanglement for scalable quantum networks. They can enhance the photon collection probability and photon generation rate of specific optical transitions and improve the coherence and spectral purity of emitted photons. For solid-state systems, open Fabry–Pérot cavities can couple single emitters that are not in proximity to the surface, avoiding significant spectral diffusion induced by the interfaces while maintaining the wide tunability, which enables addressing of multiple single emitters in the frequency and spatial domain within a single device. This review described the characteristics of single emitters as quantum memories with a comparison to atomic ensembles, the cavity-enhancement effect for single emitters and the advantages of different cavities, especially fiber Fabry–Pérot microcavities. Finally, recent experimental progress on solid-state single emitters coupled with fiber Fabry–Pérot microcavities was also reviewed, with a focus on color centers in diamond and silicon carbide, as well as rare-earth dopants.

The effect of proton irradiation with a dose of 50 Mrad (Si) on the optical properties and defect formation in crystals of gadolinium–aluminum–gallium garnet is studied during the substitution of aluminum and gallium in the cation sublattice: Gd3Al2Ga3O12 (Al : Ga = 2 : 3) and Gd3Al3Ga2O12 (Al : Ga = 3 : 2). After irradiation with protons, the crystals change color: an additional absorption band appears in the spectrum of each crystal in the wavelength range of 400–500 nm. This is due to the formation of induced structural defects in the form of color centers. The refractive indices n(λ) are determined by the Brewster spectrophotometric method and barely change for Al : Ga = 2 : 3 crystals, but largely increase for Al : Ga = 3 : 2. In the spectral dependences, there is a noticeable increase in the attenuation of light, which also indicates the formation of additional structural defects. [ABSTRACT FROM AUTHOR]

Single-photon sources are important for integrated photonics and quantum technologies, and can be used in quantum key distribution, quantum computing, and sensing. Color centers in the solid state are a promising candidate for the development of the next generation of single-photon sources integrated in quantum photonics devices. They are point defects in a crystal lattice that absorb and emit light at given wavelengths and can emit single photons with high efficiency. The landscape of color centers has changed abruptly in recent years, with the identification of a wider set of color centers and the emergence of new solid-state platforms for room-temperature single-photon generation. This review discusses the emerging material platforms hosting single-photon-emitting color centers, with an emphasis on their potential for the development of integrated optical circuits for quantum photonics. [ABSTRACT FROM AUTHOR]

Nano‐ and microcrystals of diamond are attractive for optical thermometry applications and possess unique optical properties as well as high chemical stability and biocompatibility. For biological application, there are interests of diamonds with color centers that emit in the biological transparency window. One such defect is nickel‐related color centers that radiate in the near‐infrared range (1.4 eV Ni centers), but have not yet been sufficiently investigated. In this study, the optical characteristics of high‐pressure high‐temperature (HPHT) diamond microcrystals with average sizes of 4 and 30 μm containing 1.4 eV Ni centers are reported. The temperature dependence of the spectral and temporal properties of Ni center emissions in the range from room temperature to 85 °C is demonstrated and thereby the possibility of appliance these centers as temperature sensors. The relative temperature sensitivities of luminescence peak intensity and lifetime for Ni centers are found to be 1.3% K−1 and 0.42% K−1, respectively. Moreover, the temperature determination accuracy reaches better than 1 K. [ABSTRACT FROM AUTHOR]

We report the development of multifunctional core/shell chemical vapor deposition diamond nanoparticles for the local photoinduced hyperthermia, thermometry, and fluorescent imaging. The diamond core heavily doped with boron is heated due to absorbed laser radiation and in turn heats the shell of a thin transparent diamond layer with embedded negatively charged SiV color centers emitting intense and narrowband zero-phonon lines with a temperature-dependent wavelength near 738 nm. The heating of the core/shell diamond nanoparticle is indicated by the temperature-induced spectral shift in the intensive zero-phonon line of the SiV color centers embedded in the diamond shell. The temperature of the core/shell diamond particles can be precisely manipulated by the power of the incident light. At laser power safe for biological systems, the photoinduced temperature of the core/shell diamond nanoparticles is high enough to be used for hyperthermia therapy and local nanothermometry, while the high zero-phonon line intensity of the SiV color centers allows for the fluorescent imaging of treated areas. [ABSTRACT FROM AUTHOR]

Color centers in diamonds attract significant scientific attention due to their unique photophysical properties. This mini review covers some of the most promising applications of diamonds with color centers, such as biological imaging, sensing, and quantum information processing. [ABSTRACT FROM AUTHOR]

Abstract Diamond color centers (optically active defects) can be used for all‐optical thermometry for non‐invasive and localized temperature measurements. The visible to near‐infrared photoluminescence of these defects is greatly attenuated in optical fibres and biological samples and therefore limits their use. A color center in Si‐doped diamond with emission coinciding with the O‐band and a major biological transparency window has recently been reported. It has a zero phonon line (ZPL) at 1221 nm and well‐resolved phonon side‐band features. In this work, a strong temperature dependence above 150 K is observed, allowing for accurate temperature measurements up to approximately 420 K. The temperature can be determined via spectral shifts or thermal broadening of the ZPL and through the intensity ratio between the ZPL and the phonon side‐band to a maximum temperature resolution of 0.57 K/Hz. Thermometry using these micro‐diamonds is demonstrated for both electronic and biological applications highlighting their versatility. The potential for further enhancements in sensitivity is discussed.

An experimental study of nonlinear absorption process of ultrashort laser pulses in bulk of natural diamond has been carried out. The results of experimental studies on measuring nonlinear transmission of 1 mm thick plane-parallel plate made of diamond irradiated with focused by micro lens (NA = 0.55 with focal length f ' = 5 mm) 0.3 and 10 ps laser pulses with 1030 nm wavelength are presented. It is shown that in this sample the main attenuation mechanism of ultrashort laser pulses with 1030 nm wavelength at intensities not exceeding 10 TW/cm2 is two-photon absorption at color centers, the absorption coefficient β2 = 4.1 ± 0.3 cm/TW is determined. [ABSTRACT FROM AUTHOR]

Diamond color centers have been widely studied in the field of quantum optics. The negatively charged silicon vacancy (SiV−) center exhibits a narrow emission linewidth at the wavelength of 738 nm, a high Debye–Waller factor, and unique spin properties, making it a promising emitter for quantum information technologies, biological imaging, and sensing. In particular, nanodiamond (ND)-based SiV− centers can be heterogeneously integrated with plasmonic and photonic nanostructures and serve as in vivo biomarkers and intracellular thermometers. Out of all methods to produce NDs with SiV− centers, ion implantation offers the unique potential to create controllable numbers of color centers in preselected individual NDs. However, the formation of single color centers in NDs with this technique has not been realized. We report the creation of single SiV− centers featuring stable high-purity single-photon emission through Si implantation into NDs with an average size of ∼20 nm. We observe room temperature emission, with zero-phonon line wavelengths in the range of 730–800 nm and linewidths below 10 nm. Our results offer new opportunities for the controlled production of group-IV diamond color centers with applications in quantum photonics, sensing, and biomedicine.

If the SrCl2-Tl+ crystals get irradiated with ionizing radiation at a temperature of 80-150 K, the low-temperature color centers appear in them, having surplus electric charge relative to the lattice as a result of capturing electrons and holes by the impurity-vacancy dipoles. If the crystal is irradiated at temperatures above 150 K, when the anionic vacancies can migrate, the high-temperature color centers emerge, which are electrically neutral relative to the lattice. Hence, the coloration of crystal is more effective at high temperatures. However, if the crystal irradiated at high temperatures is cooled down to 80 K, then discolored and re-irradiated with ionizing radiation, both types of color centers are effectively generated in it. Namely, SrCl2-Tl+ crystals have "radiation memory" and, as a result of such modifications, the effectiveness of crystal coloration at low temperatures increases several times. The parameters of radiation sensitivity of the SrCl2-Tl+ crystals were calculated in a one-dimensional model. The limit concentrations of the color centers as a function of the concentration of the Tl+-impurity in the crystal were defined. The calculation results are in good agreement with the experimental data, which confirms the validity of using such a one-dimensional model for predicting the radiation properties of real crystals and searching for ways to increase the effectiveness of crystal coloration. [ABSTRACT FROM AUTHOR]

• Creation of color centers in a LiF crystal by proton irradiation with a SOBP setup. • First successful visualization of proton SOBP via luminescent color centers in LiF. • Proton-beam energy spectrum reconstruction from measured photoluminescence profiles. • Preliminary comparison between SOBPs measured in LiF and expected in water. The 35 MeV proton beam produced by a modular linear accelerator was used to irradiate at grazing incidence a LiF crystal through a spinning Mylar multi-sector range modulation wheel and a Pyrex range shifter. Starting from a measured pristine depth dose curve, these energy-modulation devices were designed to plan a test shallow spread-out Bragg peak in water. The irradiation of the LiF crystal produced in its lattice a volume distribution of color centers, which could be visualized in a fluorescence microscope as a fluorescent image under blue-light illumination. Since the intensity of this fluorescent image was proportional point-by-point to the absorbed energy, it was elaborated to obtain an experimental depth dose curve in the LiF crystal, from which the proton beam energy distribution was estimated. This latter was finally used to evaluate the corresponding spread-out Bragg peak that would be obtained in water and compare it to the designed one. [ABSTRACT FROM AUTHOR]

Lithium fluoride (LiF) crystals and thin films are utilized as radiation detectors for energy diagnostics of proton beams. This is achieved by analyzing the Bragg curves in LiF obtained by imaging the radiophotoluminescence of color centers created by protons. In LiF crystals, the Bragg peak depth increases superlinearly with the particle energy. A previous study has shown that, when 35 MeV protons impinge at grazing incidence onto LiF films deposited on Si(100) substrates, the Bragg peak in the films is located at the depth where it would be found in Si rather than in LiF due to multiple Coulomb scattering. In this paper, Monte Carlo simulations of proton irradiations in the 1–8 MeV energy range are performed and compared to experimental Bragg curves in optically transparent LiF films on Si(100) substrates. Our study focuses on this energy range because, as energy increases, the Bragg peak gradually shifts from the depth in LiF to that in Si. The impact of grazing incidence angle, LiF packing density, and film thickness on shaping the Bragg curve in the film is examined. At energies higher than 8 MeV, all these quantities must be considered, although the effect of packing density plays a minor role. [ABSTRACT FROM AUTHOR]

Optically addressable defects in wide‐bandgap semiconductors are of considerable interest as materials platforms for quantum sensing and information systems. Density functional theory is used to identify novel defects in diamond consisting of transition metal + nitrogen complexes with potential for quantum sensing. Defects are characterized with respect to formation energy, ordering and degeneracy of the defect energy levels, optical and charge transition energies, zero‐field‐splitting energies, and thermodynamic stability. Novel defect sites with optically addressable spin states and viable spin sublevel configurations are identified, and analysis of activation energies for atomic migration indicates stability in the lattice. [ABSTRACT FROM AUTHOR]

The study is devoted to the radiation defects created in the calcium fluoride single crystals with reactor irradiation to the fluence of 3.7 × 1017 thermal and 4.6 × 1017 fast (En > 1 MeV) neutrons per cm2, and their effect on the luminescence of the crystals. UV–VIS absorption spectroscopy revealed the formation of point defects, mainly F and F2 centers. From the comparison of the annealing behavior of the absorption and the ion-beam-induced luminescence (IBIL), we conclude that the color centers are responsible for a non-radiation decay of self-trapped excitons (STEs) and thus cause the luminescence quenching. In addition, the Raman analysis revealed a disorder of about 44% and a stress formation in the material after the neutron irradiation. Annealing at 100 °C reduces the disorder to 13% and eliminates the stress. [ABSTRACT FROM AUTHOR]

The physical properties of diamond crystals, such as color or electrical conductivity, can be controlled via impurities. In particular, when doped with nitrogen, optically active nitrogen-vacancy centers ( N V ), can be induced. The center is an outstanding quantum spin system that enables, under ambient conditions, optical initialization, readout, and coherent microwave control with applications in sensing and quantum information. Under optical and radio frequency excitation, the Zeeman splitting of the degenerate states allows the quantitative measurement of external magnetic fields with high sensitivity. This study provides a pedagogical introduction to the properties of the N V centers as well as a step-by-step process to develop and test a simple magnetic quantum sensor based on color centers with significant potential for the development of highly compact multisensor systems. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental observation of two types of stimulated emission (SE) under pulsed laser pumping at 532 nm in diamond with NV centers. A comprehensive spectroscopic characterization of multisectorial HPHT diamond plate was performed. At low pumping power, the stimulated emission from NV¯ centers was recorded as a broad (≥80 nm wide) band with a maximum at 706 nm in the {111} and {311} sectors of the diamond plate. As the pump power increased in the {111} sector, narrow-band stimulated emission (<10 nm wide) was detected, with a maximum at 716 nm and a luminescence impulse duration of 1.5–3 ns. As the pump density increased, a fine structure in the spectrum of narrow-band stimulated emission was revealed for the first time. The concentration of NV¯ centers in the {111} and {311} growth sectors was ≈10 ppm. However, there were considerable differences in the concentrations of C (35 and 3.5 ppm) and C+ centers (6.1 and 3.2 ppm, respectively). It was demonstrated that the presence of a high concentration of NV¯ centers is not the only necessary condition for the initiation of narrow-band SE in the 710–720 nm range. In the {311} sector, lighting at 360, 405, and 488 nm reduced the concentration of NV¯ centers by 15 % while increasing the concentration of C+ centers in the {311} sector. This effect is weak in the {111} sector. The authors suggested a model for narrow-band SE at the transition Valence Band → C+ with charge-state conversion of C↔C+ and NV0↔NV¯ centers. Further research on the dynamic processes is required in order to a detailed understanding of the operation of NV centers in diamond during SE generation. [Display omitted] [ABSTRACT FROM AUTHOR]

Single-photon sources are important for integrated photonics and quantum technologies, and can be used in quantum key distribution, quantum computing, and sensing. Color centers in the solid state are a promising candidate for the development of the next generation of single-photon sources integrated in quantum photonics devices. They are point defects in a crystal lattice that absorb and emit light at given wavelengths and can emit single photons with high efficiency. The landscape of color centers has changed abruptly in recent years, with the identification of a wider set of color centers and the emergence of new solid-state platforms for room-temperature single-photon generation. This review discusses the emerging material platforms hosting single-photon-emitting color centers, with an emphasis on their potential for the development of integrated optical circuits for quantum photonics.

Annealing of color centers was studied in lithium fluoride crystals, irradiated with 23-MeV nitrogen and 28-MeV oxygen ions. Basing on the optical absorption spectroscopy and reaction-rate modelling, a new interpretation of the annealing kinetics at the practically important temperatures below 500 K is suggested. Proposed model explains simultaneous decrease of the F and F _2 /F _3 ^+ peaks as a result of migration of the F centers and formation of larger aggregates, and does not include additional assumptions about impurities and cation vacancies. It specifies the migration energy of the F centers in the ground state to be about 1.3 eV, that corresponds to earlier studies.

This work is focused on the investigation of the X‐ray's interaction with the color centers in diamond. X‐rays have the high penetrating power of radiation, which allows performing unhindered modifications deeply in the bulk of diamond crystals. Herein, it is shown that X‐rays irradiation of diamond can change the charge states of its defects, including silicon‐vacancy (SiV) and nitrogen‐vacancy (NV) color centers. By studying low‐temperature absorption spectra, it is shown that negatively charged SiV− and NV− centers partially transform into neutrally charged SiV0 and NV0 centers, accordingly. In addition, new absorption lines are registered, which may belong to other charge states of color centers. The results open a new way for the study of charge states for defects in various crystals (not limited to diamond), as well as allow the control over the charge state of color centers for diamond‐based quantum optics. [ABSTRACT FROM AUTHOR]

The radiation-induced photoluminescence (PL) of LiF has found its way into many applications for the detection and imaging of ionizing radiation. In this work, the influence of thermal treatment at temperatures up to 400 °C on absorption and PL emission spectra as well as fluorescent nuclear tracks in irradiated LiF crystals was investigated. It was found that carrying out PL measurements with the crystals kept at the temperature of about 80 °C leads to a considerable increase in luminescence emission of F3+ color centers at 525 nm. This enhancement of PL intensity allows for the microscopic imaging of the fluorescent nuclear tracks using only F3+ emission, which is not possible at room temperature. It was also found that heating the irradiated crystals before measurement at temperatures from 100 °C to 200 °C increases the concentration of F3+ centers. However, the related enhancement of PL emission is insufficient in terms of enabling the observation of the fluorescent tracks in this part of the spectrum. In the case of the main PL emission at 670 nm related to F2 centers, the thermal treatment at around 290 °C substantially increases the intensity of fluorescent tracks. This effect, however, was found to occur only at low fluences of alpha particles (up to about 109 cm−2); therefore, it is barely visible in the emission spectrum and not noticeable in the absorption spectrum. [ABSTRACT FROM AUTHOR]

The results of a study of the incorporation of silicon in diamond depending on the growth conditions of epitaxial layers in a chemical vapor deposition (CVD) reactor in a gas mixture of hydrogen, methane, and silane are presented. A detailed study of the effect of methane and silane flows, substrate temperature, gas mixture pressure, and substrate misorientation angle has been carried out. The influence of the surface misorientation angle on the formation of silicon‐vacancy (SiV) centers in diamond has been studied. It has been found that the carbon content in the gas mixture has a significant effect on the incorporation of silicon into diamond. Studies of the CVD growth of silicon‐doped diamond are carried out simultaneously with studies of the optical spectra of plasma emission in the reactor. The content of silicon in plasma is compared with content of silicon incorporated into diamond during CVD synthesis. The most efficient formation of SiV centers is observed for substrate misorientation angles from 2° to 4°. [ABSTRACT FROM AUTHOR]

The effect of a fluence of electrons with an energy of 30 keV in the range of (1–7) × 1016 cm–2 on the concentration of color centers in micron-sized hollow particles of aluminum oxide is studied in comparison with bulk Al2O3 microparticles. The analysis is carried out in situ according to diffuse reflection spectra in the range from 250 to 2500 nm. The radiation resistance of the studied microspheres is estimated relative to Al2O3 microparticles from analysis of the difference spectra of diffuse reflection obtained by subtracting the spectra after irradiation from the spectra of nonirradiated samples. Changes in the difference spectra of diffuse reflection of aluminum-oxide microparticles and microspheres show that with an increase in the electron fluence, the induced absorption increases throughout the entire spectrum. It is established that the radiation resistance of aluminum-oxide microspheres to the action of electrons with an energy of 30 keV at a fluence of (1–7) × 1016 cm–2 is greater than the radiation resistance of Al2O3 microparticles. An increase in the radiation resistance of hollow aluminum-oxide particles is due to a low concentration of radiation-induced defects in the anion sublattice. [ABSTRACT FROM AUTHOR]

The incorporation of impurity atoms into diamonds has been an important issue for the application in the area of electronics, opto-electrics, and quantum optics with color centers. To date, it remains a challenge to explore the impurity distribution in diamond films owing to the low incorporation efficiency. In this work, Si-doped diamond films were deposited in microwave CVD system. Thermal oxidation was employed to selectively etch the non-diamond phase to study the impurity distribution and evolution. For micro-/nano-sized diamond films, the micro-sized grains remain intact, while the diamond nanocrystals are oxidized into porous oxides. The diamond needles exhibit strong silicon-vacancy center optical emission at 738 nm, implying that the Si atoms are incorporated into the lattice. Detailed microstructure characterizations reveal that the porous oxides are crystallized in amorphous state, consisting of silicon, oxygen, and carbon elements. Such abundance of Si in the amorphous porous oxides suggests that the Si atoms segregate at the grain boundaries. Therefore, this work provides a new path to reveal the impurity distribution along diamond crystalline defects. Moreover, the in-situ formed silicon oxide can act as an anti-reflection coating to enhance the optical emission of color centers, which is important for their optical applications. [Display omitted] • A new approach is used to reveal the distribution of impurity atoms in diamond films. • Porous silicon oxides are formed when grain boundaries are oxidized in Si doped diamond films. • It is confirmed that Si atoms segregate along grain boundaries in diamond films. • The in-situ formed oxide film act as an anti-reflection film to enhance the optical collection efficiency of SiV centers. [ABSTRACT FROM AUTHOR]

The dynamics of color centers, being a promising quantum technology, is strongly dependent on the local environment. A synergistic approach of X‐ray fluorescence analysis and X‐ray excited optical luminescence (XEOL) using a hard X‐ray nanoprobe is applied. The simultaneous acquisition provides insights into compositional and functional variations at the nanoscale demonstrating the extraordinary capabilities of these combined techniques. The findings on cobalt doped zinc oxide nanowires show an anticorrelation between the band edge emission of the zinc oxide host and the intra‐3d cobalt luminescence, indicating two competing recombination paths. Moreover, time‐resolved XEOL measurements reveal two exponential decays of the cobalt luminescence. The fast and newly observed one can be attributed to a recombination cascade within the cobalt atom, resulting from direct excitation. Thus, this opens a new fast timescale for potential devices based on cobalt color centers in ZnO nanowires in photonic circuits. [ABSTRACT FROM AUTHOR]