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This work describes the X-ray structure of orange–red crystals of 2-methoxy-5- nitroaniline, C7H8N2O3. The compound displays concentration-dependent UVVis spectra, which is attributed to dipole-induced aggregation, and light absorption arising from an intermolecular charge-transfer process that decreases in energy as the degree of aggregation increases. The crystals display π-stacking where the dipole moments align antiparallel. Stacked molecules interact with the next stack via hydrogen bonds, which is a state of maximum aggregation. Light absorption by charge transfer can be compared to colored inorganic semiconductors such as orange–red CdS, with a band gap of 2.0– 2.5 eV. [ABSTRACT FROM AUTHOR]

The correct conditions for measuring the luminescence intensities in fi laments formed by the action of femtosecond laser pulses were found for lithium fluoride crystals. The determined conditions ensured that the measured intensities were proportional to the concentrations of luminescent color centers created in the crystals by the laser radiation and allowed conclusions to be drawn about the processes occurring in the filaments. Near-cluster color centers were found, indicating the presence of nanosized clusters in all areas of the fi laments. [ABSTRACT FROM AUTHOR]

This work describes the X-ray structure of orange–red crystals of 2-methoxy-5-nitroaniline, C7H8N2O3. The compound displays concentration-dependent UV-Vis spectra, which is attributed to dipole-induced aggregation, and light absorption arising from an intermolecular charge-transfer process that decreases in energy as the degree of aggregation increases. The crystals display π-stacking where the dipole moments align antiparallel. Stacked molecules interact with the next stack via hydrogen bonds, which is a state of maximum aggregation. Light absorption by charge transfer can be compared to colored inorganic semiconductors such as orange–red CdS, with a band gap of 2.0–2.5 eV.

When annealing a 4H silicon carbide (SiC) crystal, a sequence of optically active defect centers occurs among which the TS center is a prominent example. Here, we present low-temperature photoluminescence analyses on the single defect level. They reveal that the three occurring spectral signatures TS1, TS2 and TS3 originate from one single defect. Their polarization dependences expose three different crystallographic orientations in the basal plane, which relate to the projections of the nearest neighbor directions. Accordingly, we find a three-fold level-splitting in ensemble studies, when applying mechanical strain. This dependency is quantitatively calibrated. A complementary electrical measurement, deep level transient spectroscopy, reveals a charge transition level of the TS defect at 0.6 eV above the valence band. For a future identification, this accurate characterization of its optical and electronic properties along with their response to mechanical strain is a milestone. [ABSTRACT FROM AUTHOR]

Optically active color centers in diamond and nanodiamonds can be utilized as quantum sensors for measuring various physical parameters, particularly magnetic and electric fields, as well as temperature. Due to their small size and possible surface functionalization, fluorescent nanodiamonds are extremely attractive systems for biological and medical applications since they can be used for intracellular experiments. This review focuses on fluorescent nanodiamonds for thermometry with high sensitivity and a nanoscale spatial resolution for the investigation of living systems. The current state of the art, possible further development, and potential limitations of fluorescent nanodiamonds as thermometers will be discussed here. [ABSTRACT FROM AUTHOR]

The authors investigate the mechanism behind the formation of luminescence centers inside LiF crystals in the short-wave range (400–500 nm). The studied centers are found to be intrinsic crystal lattice defects, created by a radiation–thermal process. The proposed center model is obtained in the NaF lattice. It is established that new centers in sodium fluoride allow short-wave luminescence to be obtained in the yellow-green range. [ABSTRACT FROM AUTHOR]

An experimental demonstration of the generation of V Si , C Si V C , and N C V Si color centers in 4H–SiC using helium ion microscope irradiation of 5 × 5 μm2 areas with subsequent annealing treatment is presented. With the aid of transmission electron microscopy (TEM), photoluminescence (PL) and cathodoluminescence (CL) spectroscopy and Raman stress analysis, the evolution and distribution of color centers were thoroughly investigated. Cross-sectional TEM revealed the presence of helium bubbles in the center of the regions implanted with high doses which account for the observed quench of PL emission in the center of the implanted regions in both PL and CL measurements. PL spectra from the virgin, implanted and annealed samples proved the appearance of V Si after implantation and the transformation from V Si to C Si V C and N C V Si centers after annealing at 1000 °C. Moreover, with the increase of the implantation dose, the area of N C V Si centers increases whereas that of C Si V C decreases, which provide the first evidence of the competitive relationship between the formation of C Si V C and N C V Si defects. The comparison between stress distribution and C Si V C defect distribution illustrated that C Si V C centers predominantly distributed around the surface rupture region after thermal annealing where significant stress repair occurred. The results show that focused helium ion implantation holds promise for the precise coupling of V Si , C Si V C and N C V Si centers in predefined locations in integrated photonics applications. [ABSTRACT FROM AUTHOR]

Single-photon emitters in hexagonal boron nitride have been extensively studied recently. Although unambiguous identification of the emitters is still under intense research, carbon-related defects are believed to play a vital role for the emitter producing zero-phonon lines in the range of 1.6–2.2 eV. In this study, we systematically investigate two configurations of carbon-vacancy defects, VNCB and CNVB, by means of density functional theory calculations. We calculated the reaction barrier energies from one defect to the other to determine relative stability. We find that the barrier energies are charge dependent, and CNVB could easily transform to VNCB in neutral- and positive-charge states while it is stable when negatively charged. Formation energy calculations show that the VNCB is the dominant defect over CNVB. However, neither VNCB nor CNVB has suitable fluorescence spectra that could reproduce the observed ones. Our results indicate that the origin of the 1.6-to2.2-eV emitters should be other carbon-related configurations. [ABSTRACT FROM AUTHOR]

Optically active color centers in diamond and nanodiamonds can be utilized as quantum sensors for measuring various physical parameters, particularly magnetic and electric fields, as well as temperature. Due to their small size and possible surface functionalization, fluorescent nanodiamonds are extremely attractive systems for biological and medical applications since they can be used for intracellular experiments. This review focuses on fluorescent nanodiamonds for thermometry with high sensitivity and a nanoscale spatial resolution for the investigation of living systems. The current state of the art, possible further development, and potential limitations of fluorescent nanodiamonds as thermometers will be discussed here.

Incorporating two-dimensional (2D) diamond nanosheets with fluorescent color centers exhibits great potential in the application of quantum sensing. However, color centers always show poor optical emission in chemical-vapor-deposited (CVD) diamond nanomaterials. To address this issue, Si doped diamond/graphite hybrid films were successfully fabricated in microwave-plasma CVD device. The films consist of diamond-core/graphite-shell nanosheets with high amount of diamond nanocrystalline particles. Two post treatments of acid oxidation and annealing in air were used to tailor photoluminescence (PL) of silicon-vacancy (SiV) centers. The SiV centers in the oxidized samples exhibit small PL increase compared with the as-deposited samples with SiV PL quenching. It is found that the graphite phase is selectively etched away with the presence of nanocrystalline diamond particles during the treatment of acid oxidation while the nanocrystalline diamond particles are efficiently removed with the presence of graphite using the air annealing method. Based on this result, a two-step approach of acid oxidation followed by air annealing was conducted to etch the non-diamond phase, forming diamond nanosheets. The SiV centers exhibit significant PL enhancement with a maximum value of 28 folds, compared with the single-step oxidized samples. The Raman and XPS results reveal that such PL increase originates from direct bonding of oxygen on the sp3 carbon. Therefore, our work provides a feasible approach to prepare 2D diamond nanosheets with high-brightness color centers.

This research work focuses on investigating the darkening phenomenon in soda-lime glasses caused by the formation of color centers when exposed to infrared femtosecond laser radiation. The study examines the kinetics of color center generation and thermal relaxation, with a particular emphasis on the influence of storage temperature. Additionally, the changes in transmittance and refractive index values of darkened glass were measured based on different laser processing parameters. The darkening process can be utilized for the creation of halftone monochrome images for decorative purposes. The study also discusses the achievable contrast values and their degradation over time. Our findings were supported by direct laser writing of an image into the glass volume, highlighting their practical interest. [ABSTRACT FROM AUTHOR]

Diamond is a typical superhard multifunctional material with excellent properties such as the highest hardness, ultra-wide band gap and the highest thermal conductivity. The reserve of natural diamond is small and the price is expensive. Color diamonds are a very small part of nature diamonds and their coloring mechanisms are extremly complicated. It is a effective method to synthesize diamond by high temperature and high pressure method, but it is still a great challenge to modulate and realize color diamonds. In this paper, the quality, structural defects and impurities of color (pink and green) diamonds were studied by Raman, photuluminescence, infrared and visible absorption technologies, and the quality, defect changes with temperature and the cause of color were studied in detail. It is found that the coloring mechanism was related to electrically neutral N2 V defect (H3), shear stress, plastic deformation and NV0/NV- color center etc. Obtaining color diamonds by various methods is not only for their highly valued gemstones, but also helps people to further understand the formation mechanism of diamond, and provides a new reference for the cultivation of colored diamonds. [ABSTRACT FROM AUTHOR]

Impurity-vacancy centers in diamond offer a new class of robust photon sources with versatile quantum properties. While individual color centers commonly act as single-photon sources, their ensembles have been theoretically predicted to have tunable photon-emission statistics. Importantly, the particular type of excitation affects the emission properties of a color center ensemble within a diamond crystal. While optical excitation favors non-synchronized excitation of color centers within an ensemble, electron-beam excitation can synchronize the emitters excitation and thereby provides a control of the second-order correlation function g 2(0). In this letter, we demonstrate experimentally that the photon stream from an ensemble of color centers can exhibit g 2(0) both above and below unity, thereby confirming long standing theoretical predictions by Meuret et al. [S. Meuret, L. H. G. Tizei, T. Cazimajou, et al., “Photon bunching in cathodoluminescence,” Phys. Rev. Lett., vol. 114, no. 19, p. 197401, 2015.]. Such a photon source based on an ensemble of few color centers in a diamond crystal provides a highly tunable platform for informational technologies operating at room temperature.

Atomically thin two-dimensional (2D) hexagonal boron nitride (hBN) has emerged as an essential material for the encapsulation layer in van der Waals heterostructures and efficient deep ultraviolet optoelectronics. This is primarily due to its remarkable physical properties and ultrawide bandgap (close to 6 eV, and even larger in some cases) properties. Color centers in hBN refer to intrinsic vacancies and extrinsic impurities within the 2D crystal lattice, which result in distinct optical properties in the ultraviolet (UV) to near-infrared (IR) range. Furthermore, each color center in hBN exhibits a unique emission spectrum and possesses various spin properties. These characteristics open up possibilities for the development of next-generation optoelectronics and quantum information applications, including room-temperature single-photon sources and quantum sensors. Here, we provide a comprehensive overview of the atomic configuration, optical and quantum properties, and different techniques employed for the formation of color centers in hBN. A deep understanding of color centers in hBN allows for advances in the development of next-generation UV optoelectronic applications, solid-state quantum technologies, and nanophotonics by harnessing the exceptional capabilities offered by hBN color centers. [ABSTRACT FROM AUTHOR]

• The 3.12 eV luminescence is due the spin-allowed transition 61P 1 → 61S 0 of Tl+-ion. • Thermal electron transfer 3P 1 → 1P 1 gives rise the slow decay stage at T = 77–170 K. • Disintegration of [Tl0V k ] complexes at T > 170 K is accompanied by 3.12 eV luminescence. • The impurity conduction band electrons recombine with Tl++ centers at T>170K. The amplitude-time parameters of the A-luminescence at 3.12 eV are studied for CsI:Tl irradiated by a pulsed electron beam at temperatures 77–295 K. It has been established that the 3.12 eV band kinetics varies differently with temperature in two temperature ranges of 77–170 K and 170–295 K. The increase in temperature from 77 K to 170 K causes the decrease in the exponential decay time constant, while at temperatures above 170 K, there appeared the post-radiation rise stage followed by the slow exponential decay stage. The temperature behavior of the A-luminescence kinetics is interpreted in term of the model, according to which (i) the A band is due to the allowed electron transition 61P 1 → 61S 0 of Tl+ ions and (ii) the main excitation mechanism across the entire cathodoluminescence spectrum of CsI:Tl at temperatures near room temperature is the spontaneous disintegration of donor–acceptor dipoles [Tl0V k ]. [ABSTRACT FROM AUTHOR]

The resistance of calcium fluoride crystals to γ-irradiation is one of the key properties for its application in space. In this paper, the effect of trace La impurities on the γ-irradiation induced color center of calcium fluoride crystals was reported. The calcium fluoride crystals with trace La impurities were studied by absorption spectroscopy and electron paramagnetic resonance (EPR). The results show that the irradiated calcium fluoride crystals produce multiple color center absorption bands, and the absorption band increases with the increase of irradiation dose and the concentration of La impurities. EPR confirms that the formation of this absorption band is caused by the F color center in the calcium fluoride crystal. The presence of La3+ affect the stability and spectral position of the F centers in calcium fluoride crystals. Possible mechanisms for the presence of La3+ and F centers in calcium fluoride crystals are proposed. [ABSTRACT FROM AUTHOR]

We readdress the nature and creation mechanism of the defects absorbing at 4.7 eV in Swift Heavy Ion (SHI)-irradiated AlN semiconductor. Irradiations are performed in different controlled atmospheres (vacuum, oxygen, helium or argon partial pressure) to investigate the coupled effects of (i) the synergy between electronic excitations (S e) and nuclear collisions (S n) for point defect creation and (ii) SHI-induced impurity introduction/diffusion into the AlN layer. We found that the synergy, previously reported, between S e and S n for defect formation must also be related to the presence of oxygen during irradiation. At the same S e , the synergy parameter is indeed increased by up to two orders of magnitude during irradiation under O 2 compared to irradiation under vacuum. By SHI irradiation and by a fine-tuning of the irradiation atmosphere, we then control the activation or inhibition of these light-emitted point defects (oxygen-vacancy complexes) which can be used as qubits for applications in quantum computing. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC), as a wide-band gap semiconductor, plays an important role in high temperature and high-power devices, and the spin defect has great application prospect in quantum technology. Divacancy in SiC (V C V Si , VV) has attracted more and more attention. There are a lot of experimental studies on color center preparation by ion implantation, but the mechanism of atomic scale defects in the experimental preparation process is not fully understood. EPI epitaxial 4H–SiC was implanted with 250 keV proton at room temperature under three fluence of 1E14 cm−2, 1E15 cm−2, 1E16 cm−2. Defects of implanted 4H–SiC samples were characterized by photoluminescence spectrum and electron paramagnetic resonance (EPR). The existence of the optimal implantation fluence for V Si and V C V Si (VV) color centers by hydrogen ion implantation was found. Molecular dynamics (MD) simulation by considering the ionization energy loss for swift ion implantation were used to study the defect distribution and transformation at atomic-scale during hydrogen ion implantation and post-annealing. The optimal implantation fluence was found and confirmed by comparing the atomic-scale implantation simulation with the experimental results. In the annealing simulation, the optimal annealing temperature for the color centers in 4H–SiC was verified, and its formation mechanism was analyzed by accurately calculating the defect transformation during the annealing process. Finally, in order to accurately control the depth of color center in 4H–SiC, dual ions implantation of carbon and proton has been studied to realize the optimal divacancy yield by SRIM and MD simulations. Molecular dynamics simulation results showed that low-fluence C pre-implantation is helpful to improve the color center yield for the dual ions implantation. [ABSTRACT FROM AUTHOR]

Functional aerogels composed of regenerated cellulose and tungsten oxide were fabricated by implanting tungsten-oxide nanodots into regenerated cellulose fiber. This superfast photochromic property benefitted from the small size and even distribution of tungsten oxide, which was caused by the confinement effect of the regenerated cellulose fiber. The composite was characterized using XRD and TEM to illustrate the successful loading of tungsten oxide. The composite turned from pale white to bright blue under ambient solar irradiation in five seconds. The evidence of solar absorption and electron paramagnetic resonance (EPR) demonstrated the fast photochromic nature of the composite and its mechanism. Furthermore, carbon fiber filled with preferential growth tungsten-oxide nanorods was obtained by annealing the photochromic composite in a N2 atmosphere. This annealed product exhibited good absorption across the whole solar spectrum and revealed an excellent photothermal conversion performance. The water evaporation rate reached 1.75 kg m−2 h−1 under one sun illumination, which is 4.4 times higher than that of pure water. The photothermal conversion efficiency was 85%, which shows its potential application prospects in seawater desalination. [ABSTRACT FROM AUTHOR]

With the rapid development of NV* color centers in silicon carbide, as a new candidate for quantum technologies, have attracted increasing attention in the past ten years. To date, there are three methods of fabricating color centers in silicon carbide: ion injection, electronic irradiation, and femtosecond laser writing. Notably, these methods are too expensive for application. In this work, we use a laser writing method to produce color centers in 4H-SiC, employing a nanosecond laser. The 4H-SiC is placed on a steady optical platform, different powers (from 30 to 100 W) of the laser are used to illuminate the 4H-SiC, and a special array of color centers is produced on different pieces of the 4H-SiC with a size of 4×4 mm. Around the array, several optically-detected color centers appear. The fabricated color centers are optically characterized by confocal imaging with a 532 nm excitation at room temperature. The fluorescence spectra certainly show that the color centers are successfully produced. The Raman spectrum shows approximately 2,000 counts of the color center ensemble. The method clearly results in fabricated silicon vacancy color centers that can emit in both ranges of 850 – 950 nm and 650 – 750 nm. This technique can be used to engineer color centers in SiC for the single-photon generation, sensing, display fabrication, and light emitting diodes. [ABSTRACT FROM AUTHOR]

Vacancy-related color centers in diamonds, such as nitrogen-vacancy (NV) and silicon-vacancy (SiV) centers, have good application prospects in solid-state quantum technologies. In various applications, shot noise-limited sensitivity is determined by coherence time and photoluminescence (PL) intensity, which depends on the color center density. However, the conversion efficiencies of impurity atoms to color centers are low and usually increased by electron irradiation, which destroy the lattice structure and create defects leading to decoherence. In this study, we epitaxially grew diamond layers containing color centers on surfaces coated with metal stripes. The PL intensities of NV0, NV−, and SiV− centers located directly above the metal surface were 3.27, 3.47, and 11.15 times higher than those of the diamond epitaxial region. The [N]–[NV] and [Si]–[SiV] conversion efficiencies were 63.26% and 35.68%, respectively, which were comparable to or even better than those achieved by electron irradiation. Moreover, the region above the metal exhibited a high lattice quality, longer transverse relaxation time, higher magnetic field sensitivity, and larger NV−/NV0 ratio. The findings of this study can help advance the existing research on NV-based magnetometers, biofluorescent labeling, and interfacial spin quantum memory and be potentially applied to other vacancy-related color centers, such as germanium-vacancy. [Display omitted] • Diamond layers with color centers are grown on surfaces with periodic metal stripes. • The color centers above the metal surface exhibit high photoluminescence intensity. • The enhanced conversion efficiencies of impurity atom to color centers exceed those enhanced by ion implantation. • The spin coherence time, magnetic field sensitivity, and ratio of NV−/NV0 are also improved. [ABSTRACT FROM AUTHOR]

Silicon-vacancy (SiV) centers in diamond are a promising candidate for all-optical nanoscale high-sensitivity thermometry because they have sufficient sensitivity to reach the subkelvin precision required for application to biosystems. It is expected that nanodiamonds with SiV centers can be injected into cells to measure the nanoscale local temperatures of biosystems such as organelles. However, the smallest particle size used to demonstrate thermometry using SiV centers is a few hundred nanometers. We recently developed SiV-center-containing nanodiamonds via a detonation process that is suitable for large-scale production. Here, we investigate the spectral response of SiV-center-containing detonation nanodiamonds (SiV-DNDs) to temperature. We used air-oxidized and polyglycerol-coated SiV-DNDs with a mean particle size of around 20 nm, which is the smallest size used to demonstrate thermometry using color centers in nanodiamond. We found that the zero-phonon line for SiV-DND is linearly red-shifted with increasing temperature in the range of 22.0–40.5 °C. The peak sensitivity to temperature was 0.011 ± 0.002 nm/K, which agrees with the reported high sensitivity of SiV centers in bulk diamond. A temperature sensitivity analysis revealed that SiV-DND thermometry can achieve subkelvin precision. All-optical SiV-DND thermometry will be important for investigating nanosystems such as organelles in living cells. [Display omitted] [ABSTRACT FROM AUTHOR]

Single-photon emitters in hexagonal boron nitride have been extensively studied recently. Although unambiguous identification of the emitters is still under intense research, carbon-related defects are believed to play a vital role for the emitter producing zero-phonon lines in the range of 1.6-2.2 eV. In this study, we systematically investigate two configurations of carbon-vacancy defects, VNCB and CNVB, by means of density functional theory calculations. We calculated the reaction barrier energies from one defect to the other to determine relative stability. We find that the barrier energies are charge dependent, and CNVB could easily transform to VNCB in neutral- and positive-charge states while it is stable when negatively charged. Formation energy calculations show that the VNCB is the dominant defect over CNVB. However, neither VNCB nor CNVB has suitable fluorescence spectra that could reproduce the observed ones. Our results indicate that the origin of the 1.6-to-2.2-eV emitters should be other carbon-related configurations. [ABSTRACT FROM AUTHOR]

Atomically thin two-dimensional (2D) hexagonal boron nitride (hBN) has emerged as an essential material for the encapsulation layer in van der Waals heterostructures and efficient deep ultraviolet optoelectronics. This is primarily due to its remarkable physical properties and ultrawide bandgap (close to 6 eV, and even larger in some cases) properties. Color centers in hBN refer to intrinsic vacancies and extrinsic impurities within the 2D crystal lattice, which result in distinct optical properties in the ultraviolet (UV) to near-infrared (IR) range. Furthermore, each color center in hBN exhibits a unique emission spectrum and possesses various spin properties. These characteristics open up possibilities for the development of next-generation optoelectronics and quantum information applications, including room-temperature single-photon sources and quantum sensors. Here, we provide a comprehensive overview of the atomic configuration, optical and quantum properties, and different techniques employed for the formation of color centers in hBN. A deep understanding of color centers in hBN allows for advances in the development of next-generation UV optoelectronic applications, solid-state quantum technologies, and nanophotonics by harnessing the exceptional capabilities offered by hBN color centers.

The results of the procedure of the volumetric-spatial mapping of firing conditions by the UV–VIS–NIR spectrum of ceramic bricks from one batch by the multivariate analysis methods are presented. The principal component method identified the absorption bands of the spectrum, which are attributed to the color centers of iron-containing impurities. The discriminant ability of color coordinates a* > b* > L* is determined when grading products into groups of samples with similar color characteristics. The volumetric-spatial mapping of firing conditions by UV–VIS–NIR spectra of ceramic products makes it possible to select samples for testing at control points according to the volume of a batch of products. [ABSTRACT FROM AUTHOR]

In this paper, the low-temperature Raman and photoluminescence (PL) spectroscopy were employed to study the crystallization degree, stress distribution of the pure diamond film. Combined with electron irradiation and rapid annealing, the impurity defect structure of the pure diamond film was studied. Raman spectroscopy analysis shows that the stress distributions in edge and surface of the film are higher than in interior, which may be ascribed to the diamond growth mechanism, physical cutting and polishing damage to the films. The zero phonon lines in PL spectra show obvious temperature dependent, and the spectra peaks redshift, intensity reduction and low-temperature splitting with increase of temperature were explained by Jahn)Teller effect and electron-phonon coupling theory. Low temperature PL spectra observed distinct NV defects in the film after electron irradiation and 700 ℃ annealing, which indicate that the nitrogen mainly existed in the lattice with a form of substitution impurities. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition ( CVD) technology has enabled synthetic diamonds to be applied in many fields, in which the excellent comprehensiveness of diamond has been fully developed, and may lead to a leap-forward development. The color center makes the diamond quantum accelerator initially show the feasibility of great power. Various scenarios, including the application of UV laser writing technology windows, maximize the comprehensive advantages of diamond windows in terms of optics, electricity, heat and mechanics. Ultra-wide bandgap diamond semiconductor applications will soon be realized, and diamond heat dissipation applications are constantly expanding. By summarizing the preparation methods and characteristics of CVD diamond, according to the intrinsic characteristics of diamond, CVD diamond is classified into quantum grade, electronic grade, optical grade, thermal grade and mechanical grade. The current status of research and application of CVD diamond are reviewed in detail, which is of great significance for judging the future development trend of CVD diamond. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation is adopted to discover the formation mechanism of silicon vacancy color center and to study the damage evolution in 4H-SiC during helium ion implantation with different annealing temperatures. The number and distribution of silicon vacancy color centers during He ion implantation can be more accurately simulated by introducing the ionization energy loss during implantation. A new method for numerical statistic of silicon vacancy color centers is proposed, which takes into account the structure around the color centers and makes statistical results more accurate than the Wignerâ€"Seitz defect analysis method. Meanwhile, the photoluminescence spectra of silicon vacancy color centers at different helium ion doses are characterized to verify the correctness of the numerical analysis. The new silicon vacancy color center identification method can help predicting the optimal annealing temperature for silicon vacancy color centers, and provide guidance for subsequent color center annealing experiments. [ABSTRACT FROM AUTHOR]

We designed a nanoscale light extractor (NLE) for the efficient outcoupling and beaming of broadband light emitted by shallow, negatively charged nitrogen-vacancy (NV) centers in bulk diamond. The NLE consists of a patterned silicon layer on diamond and requires no etching of the diamond surface. Our design process is based on adjoint optimization using broadband time-domain simulations and yields structures that are inherently robust to positioning and fabrication errors. Our NLE functions like a transmission antenna for the NV center, enhancing the optical power extracted from an NV center positioned 10 nm below the diamond surface by a factor of more than 35, and beaming the light into a ±30° cone in the far field. This approach to light extraction can be readily adapted to other solid-state color centers.

Solid state quantum emitters are a prime candidate in distributed quantum technologies since they inherently provide a spin-photon interface. An ongoing challenge in the field, however, is the low photon extraction due to the high refractive index of typical host materials. This challenge can be overcome using photonic structures. Here, we report the integration of V2 centers in a cavity-based optical antenna. The structure consists of a silver-coated, 135 nm-thin 4H-SiC membrane functioning as a planar cavity with a broadband resonance yielding a theoretical photon collection enhancement factor of ∼34. The planar geometry allows us to identify over 20 single V2 centers at room temperature with a mean (maximum) count rate enhancement factor of 9 (15). Moreover, we observe 10 V2 centers with a mean absorption line width below 80 MHz at cryogenic temperatures. These results demonstrate a photon collection enhancement that is robust to the lateral emitter position.

Functional aerogels composed of regenerated cellulose and tungsten oxide were fabricated by implanting tungsten-oxide nanodots into regenerated cellulose fiber. This superfast photochromic property benefitted from the small size and even distribution of tungsten oxide, which was caused by the confinement effect of the regenerated cellulose fiber. The composite was characterized using XRD and TEM to illustrate the successful loading of tungsten oxide. The composite turned from pale white to bright blue under ambient solar irradiation in five seconds. The evidence of solar absorption and electron paramagnetic resonance (EPR) demonstrated the fast photochromic nature of the composite and its mechanism. Furthermore, carbon fiber filled with preferential growth tungsten-oxide nanorods was obtained by annealing the photochromic composite in a N2 atmosphere. This annealed product exhibited good absorption across the whole solar spectrum and revealed an excellent photothermal conversion performance. The water evaporation rate reached 1.75 kg m−2 h−1 under one sun illumination, which is 4.4 times higher than that of pure water. The photothermal conversion efficiency was 85%, which shows its potential application prospects in seawater desalination.

In this paper, we summarize the research on photodarkening in optical fibers. The causes of photodarkening in fiber, the influence of photodarkening on fiber laser, the experimental device of photodarkening, and the mathematical model used to study the phenomenon of photodarkening are described in detail. At the end of the paper, we summarize the means and methods to suppress photodarkening. [ABSTRACT FROM AUTHOR]

Atomic and close-to-atomic scale fabrication with high yield for the color centers in silicon carbide is critical in developing its applications. Combined with Wigner-Seitz method and identify diamond structure method to consider the structure around the silicon vacancy (V Si), it is found that He ion implantation is more likely to fabricate a small number of silicon vacancies with complete structure but locating deep, while Si ion implantation is more likely to introduce more silicon vacancies with incomplete structure but a large number and closer to the near surface. Therefore, a method of dual ion implantation is proposed in this paper. By adjusting the ratio of He to Si ion concentration for dual ion implantation, the fabrication yield of color centers with depth below 5 nm can be increased compared with that of He implantation after high temperature annealing. Molecular dynamics (MD) simulation is employed to discover the underlying mechanism of V Si color center and damage evolution by helium ion and dual ion implantation into four-hexagonal silicon carbide (4H–SiC) with subsequent annealing. Density-functional theory (DFT) calculation proves that magnetic-spin polarization enhances the stability of carbon anti-vacancy pair (C Si V C) defect, which indicates C Si V C defects are more stable than V Si defects. The evolution of the V Si color centers of different defect models are also calculated at various temperatures by MD, and the dynamic process of V Si defects to C Si V C defects is demonstrated. It is revealed that the decrease of the V Si color center at high temperature annealing is partly due to the transformation of some silicon vacancies to C Si V C defects. • Molecular dynamics of implantation and annealing were studied the fabrication of Si vacancy color center in silicon carbide. • The calculation accuracy of Si vacancy color center was increased by considering the configuration of color center around. • He + Si dual ion implantation was adopted to increase the fabrication yield of near surface SiC color center with depth <5 nm. • The dynamic transition of silicon vacancy to C Si V C during different annealing temperatures was simulated by MD method. [ABSTRACT FROM AUTHOR]

Diamonds exhibit a unique combination of numerous excellent physical and chemical properties, such as the highest hardness, high Young's modulus, wide bandgap, high carrier mobility, negative electron affinity, and high thermal conductivity. Especially, diamond has attracted significant attention in recent years for its outstanding performance in high-frequency and high-power electronic devices and thermal management. Inheriting the intrinsic physical and chemical properties of diamonds, one-dimensional (1D) diamond nanostructures exhibit many additional properties that are unavailable for bulk diamond or thin films, e.g., large specific surface area, ultrahigh elasticity, and some plasticity, tip effect as well as direct transport for photon or photo-induced carriers. These properties make 1D diamond nanostructures an ideal candidate for applications ranging from micro/nano-electromechanical systems (MEMS/NEMS) to field electron emission, optical, electrochemical, and biological areas. This review will first introduce the development of controlled synthesis methods of 1D diamond nanostructure, including bottom-up chemical vapor deposition growth and top-down selective etching of bulk diamond. Subsequently, we will summarize recent advances in the mechanical, electron field emission, optical, and biological properties of 1D diamond nanostructures and their applications in electron and photon emitter, MEMS, sensing, intracellular delivery, etc. [Display omitted] [ABSTRACT FROM AUTHOR]

The ST1 center is a point defect in diamond with bright fluorescence and a mechanism for optical spin initialization and readout. The center has impressive potential for applications in diamond quantum computing as a quantum bus to a register of nuclear spins. This is because it has an exceptionally high readout contrast, and unlike the well-known nitrogen-vacancy center, it does not have a ground state electronic spin that decoheres the nuclear spins. However, its chemical structure is unknown, and there are large gaps in our understanding of its properties. We present the discovery of ST1 centers in natural diamond. Our experiments identify interesting power dependence of the center’s optical dynamics and reveal new electronic structure. We also present a theory of its electron-phonon interactions, which we combine with previous experiments, to shortlist likely candidates for its chemical structure.

Multi-plate sapphire crystals were grown by EFG technique. Micro-laser Raman spectrum and ICP-AES were used to identify the chemical composition of the matters in bubbles, showing that these matters may contain sulphur. Growth striations at the surface of the crystal were concerned with fluctuation of growth rate and temperature as well as the working accuracy of the die. Chemical etching test shows that the crystal has a dislocation density of 4.2 ×104 cm-2 and there is no low angle grain boundary defect. X-ray rocking curve measurement shows a single peak with FWHM of 70. 63″. Owing to graphite heat shade, the crystal contains F and F+ centers. The transmittance of the crystal is over 80% at light wavelength from 400 nm to 3 000 nm. Annealing the crystal in air can reduce optical absorption caused by color centers. The results of this paper are useful to theoretical study on formation of defects in sapphire and technical improvement on EFG sapphire industury. [ABSTRACT FROM AUTHOR]

The results of a study of the use of non-destructive contact-free optical spectroscopy — registration of UV-VIS-NIR-range diffuse reflection spectra and photoluminescence spectra — for the identification of porcelain products are reported. Based on the color characteristics and a list of optically active centers of luminescence (OALC) porcelain products were graded according to the composition and state of the redox medium during firing. It is shown that the chromaticity of porcelain can be controlled by means of a combination of color and luminescence centers and their intensity ratio. A decrease in the intensity of the OALC Fe3+ band is mainly related to a change in the coordination of iron Fe3+O4 → Fe3+O6 in bone china. [ABSTRACT FROM AUTHOR]

In this study, Yb/Al/Ge co-doped silica fiber core glasses with different GeO2 contents (0–6.03 mol%) were prepared using the sol–gel method combined with high-temperature sintering. The absorption, fluorescence, radiation-induced absorption, continuous-wave electron paramagnetic resonance spectra, and fluorescence decay curves were recorded and analyzed systematically before and after X-ray irradiation. The effects of GeO2 content on the valence variations of Yb3+/Yb2+ ions, spectral properties of Yb3+ ions, and radiation resistance of Yb/Al/Ge co-doped silica glasses were systematically studied. The results show that even if the GeO2 content of the sample is relatively low (0.62 mol%), it can inhibit the generation of Yb2+ ions with slight improvement in the spectral properties of Yb3+ ions in the pristine samples and effectively improve its radiation resistance. Direct evidence confirms that the generation of trapped-electron centers (Yb2+/Si-E’/Al-E’) and trapped-hole centers (Al-OHC) was effectively inhibited by Ge co-doping. This study provides a theoretical reference for the development of high-performance, radiation-r esistant Yb-doped silica fibers.

SiC is always produced forming diamond/SiC composite films owing to the oversaturated doping of Si atoms during the preparation of high emission SiV centers. As a higher refractive index material (n = 2.72), the presence of SiC could possibly lead to inefficient photo-luminescent (PL) collection of SiV centers with total internal reflection. In order to understand such effect, different diamond/SiC films were deposited in a 915 MHz microwave plasma CVD (MPCVD) using the reactive gas of tetramethylsilane (TMS). The microstructure and photoluminescence of SiV centers were systematically investigated. It is found that the addition of TMS gas leads to the formation of cubic β-SiC and the refinement of diamond crystals. At the TMS gas flow of 5 sccm, the concentration of β-SiC is about 10% and the average diamond size is about 98 nm. The film exhibits the optimized PL emission of SiV centers, with the ratio of SiV PL to diamond Raman peak being 21.4. Increasing TMS gas flow leads to the increase of the concentration of β-SiC and the deterioration of PL emission of SiV centers. These results reveal that the introduction of TMS gas at a low flow advances the formation of diamond/SiC film containing high-brightness SiV centers. The diamond/SiC composite film at SiC concentration of 10% exhibits the optimized PL collection of SiV centers (the 2# sample). Image 1 [ABSTRACT FROM AUTHOR]

We designed a nanoscale light extractor (NLE) for the efficient outcoupling and beaming of broadband light emitted by shallow, negatively charged nitrogen-vacancy (NV) centers in bulk diamond. The NLE consists of a patterned silicon layer on diamond and requires no etching of the diamond surface. Our design process is based on adjoint optimization using broadband time-domain simulations and yields structures that are inherently robust to positioning and fabrication errors. Our NLE functions like a transmission antenna for the NV center, enhancing the optical power extracted from an NV center positioned 10 nm below the diamond surface by a factor of more than 35, and beaming the light into a ±30° cone in the far field. This approach to light extraction can be readily adapted to other solid-state color centers. [ABSTRACT FROM AUTHOR]