Generation Of Color Centers Research Articles

Selective Generation of V2 Silicon Vacancy Centers in 4H-Silicon Carbide.

The deterministic generation of individual color centers with defined orientations or types in solid-state systems is paramount for advancements in quantum technologies. Silicon vacancies in 4H-silicon carbide (4H-SiC) can be formed in V1 and V2 types. However, silicon vacancies are typically generated randomly between V1 and V2 types with similar probabilities. Here, we show that the preferred V2 centers can be selectively generated by focused ion beam (FIB) implantation on the m-plane in 4H-SiC. When implantation is on the m-plane (a-plane), the generation probability ratio between V1 and V2 centers increase exponentially (remains constant) with decreasing FIB fluences. With a fluence of 10 ions/spot, the probability to generate V2 centers is seven times higher than V1 centers. Our results represent a critical step toward the deterministic creation of specific defect types.

Defects distribution and evolution in selected-area helium ion implanted 4H–SiC

An experimental demonstration of the generation of VSi, CSiVC, and NCVSi 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 VSi after implantation and the transformation from VSi to CSiVC and NCVSi centers after annealing at 1000 °C. Moreover, with the increase of the implantation dose, the area of NCVSi centers increases whereas that of CSiVC decreases, which provide the first evidence of the competitive relationship between the formation of CSiVC and NCVSi defects. The comparison between stress distribution and CSiVC defect distribution illustrated that CSiVC 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 VSi, CSiVC and NCVSi centers in predefined locations in integrated photonics applications.

Generation of Color Centers and Laser Plasma in LiF during Multipulse Filamentation

Generation of Color Centers and Laser Plasma in LiF during Multipulse Filamentation

Rod-Type Ce/Cr/Nd : YAG Ceramic Lasers with White-Light Pump Source

Ceramic is promising for use as a solid-laser material pumped with solar or lamp light. We developed a Cr3+ ion doped Nd : YAG ceramic laser that converts white light into near-infrared laser light more efficiently. Investigation of its optical properties has revealed that large gain can be realized with excitation power that is one order of magnitude less than that in the case of Nd : YAG. Ce3+ ion doping also makes it possible to utilize the excitation light components with wavelengths of 350 nm or less, preventing generation of color centers. A rod-type Ce3+/Cr3+/Nd : YAG ceramic pumped by white light such as solar light or flash lamp light was developed. Fluorescence lifetime of ceramic was measured. Laser oscillations at free running mode were observed. Also, numerical calculation for output laser power and gain at lasing threshold was performed. Fluorescence lifetime increased as temperature rose, which was observed in Cr/Nd : YAG ceramic. This increase suggests the existence of a cross-relaxation effect. Maximum output laser energy of 73 mJ with the peak power of 330 W was obtained. Obtained output laser energy was around twice more than that in case of Cr3+/Nd : YAG ceramic with the same Nd and Cr ion concentration.

Photochromic and Electric Field-Regulating Luminescence in High-Transparent (K,Na)NbO3-Based Ferroelectric Ceramics with Two-Phase Coexistence.

Rare earth Tb3+ doped (K0.465Na0.465Li0.07)(Nb0.93Bi0.07)O3 (KNNLB-x%Tb) lead-free transparent ferroelectric ceramics were designed and prepared. The effects of Tb3+ on phase structure, microstructure, optical transmittance, photoluminescence, and photochromic behaviors were studied. Although two ferroelectric phases coexist, the optical transmittance can reach the high value of 74% in the visible light region because of the fine grains, dense ceramic microstructure, large optical energy band gap, and relatively high symmetry of coexisting ferroelectric phases. In addition, Tb3+ works as a luminescent center, and the reversible photochromic modulation is achieved by alternate stimulation of illumination and heat treatment. Meanwhile, the luminescence contrast can be improved under in situ electric field stimulation due to the easy change of lattice symmetry in coexisting ferroelectric phases. The generation of color centers after illumination and the local crystal field around the luminescent center caused by in situ electric field contributes to above phenomena. These ceramics exhibit the great potential in optical data storage and anticounterfeiting.

Tunable color generation in CdTe-doped silicate glass enabled by ultrashort laser pulses: interior coloring and multilevel encryption.

The launch of the big data era puts forward challenges for information security. Herein, a new kind of silicate glass system co-doped with CdO and ZnTe, capable of achieving the controllable generation of intrinsic color centers (brown and green) and tiny nuclei of CdTe via direct laser writing (DLW), is developed. The controlled growth of CdTe QDs thermally, leads to a permanent color of orange at the cost of accelerated aging of the color centers of brown and green. On the one hand, going beyond traditional 2D surface coloration, the high transparency of the studied bulk medium makes 3D volumetric interior coloration possible. On the other hand, by encoding ciphertext into the tiny nuclei of CdTe, a strategy of color encryption and heat decryption is established, which brings about the merits of expanded storage capacity and improved information security. The demonstration application confirmed the user-defined multiscale interior coloration and an unprecedented multidimensional color-encryption scheme with a high-security level. The present work highlights a great leap in transparent materials for color encryption and hopefully stimulates the development of new color division multiplexing encryptions.

Radiation-induced color centers and their inhibition methods in Yb3+-doped silica fibers

Yb3+-doped silica fiber (YDF) lasers have important application prospects in space. However, YDFs face various types of harsh ionizing radiation (such as protons, electrons, and γ-rays) during space missions. Radiation-induced darkening (RD), primarily because of the generation of color centers at a microscopic scale, can seriously deteriorate the laser performance of the YDFs. In this review, the nature, formation mechanism, and suppression methods of color centers in YDFs are introduced.

Parameters Optimization of ASE Source for the Improvement of Optical Power Stability in Space Radiation Environment

A parameter optimization model of amplified spontaneous emission (ASE) source in space radiation environment has been developed based on the ASE source model and the radiation-induced attenuation (RIA) model of erbium-doped fiber (EDF). The RIA model considers color center generation and annealing process at the same time. Using the radiation attenuation and recovery spectra obtained at the dose rate of 30 Gy/min, the color center generation and recovery parameters in the EDF are obtained. Based on the ASE source model, the parameter optimization model at the high dose rate of 30 Gy/min is established. Then, the model is successfully extrapolated to a small dose rate of 0.06 Gy/min. These effects of the spectral shape, pump power, and fiber length on the output power stability of the ASE source are investigated using this model at the dose of 0.06 Gy/min. Finally, the experiment is performed to evaluate the simulation, and it is suggested that the output power fluctuation of the optimized ASE source is less than 3% within the radiation dose range of 300 Gy.

Radiation‐induced darkening and its suppression methods in Yb3+‐doped silica fiber core glasses

AbstractYb3+‐doped silica fiber (YDF) laser has important applications in space. However, the darkening effect caused by space ionizing radiation (called RD effect), which is due to the generation of color centers at the microscopic scale, can significantly deteriorate the performance of the YDF laser. This review mainly includes three aspects. First, we briefly introduce space radiation environment and challenges that optical fibers encounter in space. Second, we review the nature and generation mechanism of color centers responsible for RD in YDFs. Finally, we systematically introduce five methods to inhibit RD and their inhibition mechanisms.

Photo-response of polylactide-poly(methyl methacrylate) blends: Effect of ultraviolet irradiation

The applications of biodegradable polylactide (PLA) are dependent on its structural durability under service conditions. In this work, we analyze the temperature dependence of photo-stability of polylactide-poly(methyl methacrylate) (PLA/PMMA) blends after the irradiation of ultraviolet (UV) light. X-ray diffraction analysis of the UV-irradiated PLA reveals the crystalline phase formation at 55 °C, as confirmed by thermal analysis. The UV irradiation decreases the crystallization temperature of PLA. The thermal analysis and Fourier Transform Infra-Red (FT-IR) analysis illustrate the interaction between PLA and PMMA. We evaluate the photo-stability of the UV-irradiated PLA/PMMA blends from the temporal evolution of optical absorbance/transmittance of the blends. A first-order kinetic analysis is used to analyze the change of optical absorbance, controlled by the annihilation and generation of color centers. Two processes contribute to the photo-stability of the PLA/PMMA blends – one is annihilation-dominant for the blends with a large fraction of PMMA, and the other is generation-dominant for the blends with a large fraction of PLA. The combinational effect of UV irradiation and the interaction between PLA and PMMA determines the photo-stability of PLA/PMMA blends.

Effect of X-ray irradiation on the properties of alumina ceramics

Alumina ceramics are commonly used as high-voltage insulation materials. The alumina ceramic will turn yellow after being irradiated with a certain amount of X-rays. Based on this phenomenon, we focused on the study of the yellowing mechanism and the effect of X-ray irradiation on the electrical insulation properties of alumina ceramics. The results indicate that after X-rays irradiating on the alumina ceramic, the color becomes yellow due to the generation of color centers; within an irradiation dose of 3 mGy, X-rays have no adverse effect on the electrical insulation properties of the alumina ceramic.

Generation of Tin-Vacancy Centers in Diamond via Shallow Ion Implantation and Subsequent Diamond Overgrowth.

Group IV color centers in diamond have garnered great interest for their potential as optically active solid-state spin qubits. The future utilization of such emitters requires the development of precise site-controlled emitter generation techniques that are compatible with high-quality nanophotonic devices. This task is more challenging for color centers with large group IV impurity atoms, which are otherwise promising because of their predicted long spin coherence times without a dilution refrigerator. For example, when applied to the negatively charged tin-vacancy (SnV-) center, conventional site-controlled color center generation methods either damage the diamond surface or yield bulk spectra with unexplained features. Here we demonstrate a novel method to generate site-controlled SnV- centers with clean bulk spectra. We shallowly implant Sn ions through a thin implantation mask and subsequently grow a layer of diamond via chemical vapor deposition. This method can be extended to other color centers and integrated with quantum nanophotonic device fabrication.

Радіаційна чутливість іонних кристалів. Одновимірна модель. Кристали з дефектами дипольного типу

Виникнення радіаційного забарвлення в іонних кристалах є результатом локалізації створених радіацією вільних носіїв заряду на дорадіаційних точкових дефектах кристалічної ґратки. Із накопиченням у кристалах центрів забарвлення вступають в дію зворотні процеси. Вільні носії заряду рекомбінують на центрах забарвлення, дорадіаційні дефекти відновлюються. Завдяки довготривалого опромінення кристалів встановлюється динамічна рівновага між процесами генерації центрів забарвлення та висвітлювальною дією рентгенівських променів. Запропоновано одновимірну модель іонних кристалів, у якій було розраховано параметри радіаційної чутливості кристалів флюоритів, легованих неізовалентними домішками. Імовірність генерації центрів забарвлення при розпаді електронно-діркової пари та імовірність висвітлювальної дії знижується зі зменшенням концентрації активатора. За високих температур незалежно від концентрації активатора в кристалі імовірність утворення центрів забарвлення під час розпаду електронно-діркової пари така ж, як імовірність їх руйнування. Це пояснено тим, що в обох випадках носії заряду взаємодіють із електронейтральними дипольними центрами. Зі зменшенням концентрації активатора зростає величина енергії, що витрачається на створення однієї комплементарної пари центрів забарвлення, а відповідно радіаційна чутливість кристала знижується.

Design and fabrication of 1D and 2D optical scanner for electron beams using color centre generation

The present paper focuses on the design and fabrication of 1D and 2D optical scanners to characterize the spatial profile of electron beams. The basis of the two systems is the generation of color centers in glass plates by irradiation, followed by the scanning of the plates, illuminated by a fixed power source (LED) with a maximum power of 3 W in the spectral range of 520–560 nm, with a TCS3200 sensor. In both systems, 6 mm thick glass blades (SiO2:76%) are used instead of expensive dosimetric films. The experimental results section first focuses on the validation and calibration accuracy of the effective absorbance of the irradiated glass in the LED spectral range with a radiation dose of up to 20 kGy. Then, it describes how the 1D optical scanner was used to scan the spatial profile obtained under the scanning horn of a Rhodotron accelerator with a maximum radiation dose of 7.8 kGy. The experimental results obtained from this method are entirely consistent with the results of other research studies, while this method is more cost-efficient and accurate compared to the previously reported methods. The 2D optical scanner was also used to accurately measure the spatial profile of the Rhodotron electron beam in static mode by scanning the color centers generated by irradiation.

Photodarkening-resistance improvement of Yb3+/Al3+ co-doped silica fibers fabricated via sol-gel method.

Yb3+/Al3+ co-doped silica fibers (YDFs) with almost identical core glass compositions were prepared using the sol-gel and modified chemical vapor deposition (MCVD) methods. The photodarkening (PD) and laser performance before and after the PD process were tested under 974 nm pumping. The doping homogeneity of Yb3+ ions and clusters of Yb3+ ions in preform slices of these two fibers were investigated via optical absorption spectroscopy, photoluminescence emission spectra, electron probe microanalysis (EPMA), and low-temperature (4 K) electron paramagnetic resonance (EPR). It is known that the PD resistance of YDFs prepared via the sol-gel method is significantly better than that of YDFs prepared via MCVD under the same test conditions. EPMA mapping reveals that the doping homogeneity of Yb3+ ions in the sol-gel fiber core glass is better than that in the MCVD fiber. The low-temperature (4 K) EPR and cooperative luminescence spectra of Yb3+ ions indicate that the clustering degree of Yb3+ ions in the sol-gel fiber is lower than that in the MCVD fiber. In the absorption and emission spectra, small amounts of Yb2+ ions are observed in the preform slice from the sol-gel method. A model of the color-center generation in the PD process was proposed to explain the mechanism of PD resistance improvement for the YDFs fabricated via the sol-gel method.

Controlled generation of intrinsic near-infrared color centers in 4H-SiC via proton irradiation and annealing

We report on the generation and annihilation of color centers in 4H silicon carbide (SiC) by proton irradiation and subsequent annealing. Using low-temperature photoluminescence (PL), we study the transformation of PL spectra for different proton doses and annealing temperatures. Among well reported defect signatures, we observe omnipresent but not yet identified PL signatures consisting of three sharp and temperature stable lines (denoted TS1,2,3) at 768.8 nm, 812.0 nm, and 813.3 nm. These lines show a strong correlation throughout all measurement parameters, suggesting that they belong to the same microscopic defect. Further, a clear dependence of the TS1,2,3 line intensities on the initial implantation dose is observed after annealing, indicating that the underlying defect is related to implantation induced intrinsic defects. The overall data suggest a sequential defect transformation: proton irradiation initially generates isolated silicon vacancies which are transformed into antisite vacancy complexes which are, in turn, transformed into presumably intrinsic-related defects, showing up as TS1,2,3 PL lines. We present recipes for the controlled generation of these color centers.

Origin of Radiation-Induced Darkening in Yb3+/Al3+/P5+-Doped Silica Glasses: Effect of the P/Al Ratio.

Yb3+/Al3+/P5+-co-doped silica glasses with different P/Al ratios were prepared using the sol-gel method combined with high-temperature sintering. The evolution of composition-dependent color centers caused by X-ray irradiation in these glasses was correlated with their structural changes, which are controlled by the P/Al ratio. Nuclear magnetic resonance (NMR) and Raman spectra have been used to characterize the glass network structure, and advanced pulse electron paramagnetic resonance (EPR) has been employed to study the local coordination atomic structures of Yb3+ ions in pristine glasses as a function of the P/Al ratio. Si- (Si-E'), Al- (Al-E', Al-ODC, AlOHC), P- (P1, P2, POHC), and Yb-related (Yb2+) color centers in irradiated glasses have been observed and explained by optical absorption and continuous wave-EPR spectroscopies. The formation mechanisms of these centers, the structural models of glasses, and the relationship between them were proposed. Direct evidence confirms that the formation of Yb2+ ions induced by radiation is highly dependent on the coordination environment of Yb3+ ions in glasses. In addition, the glass network structure significantly affects the generation of oxygen hole color centers (AlOHCs/POHCs) caused by radiation. These results are useful in understanding the microstructural origin and the suppression mechanism of the radiodarkening effect by phosphorus co-doping in Yb3+-doped silica fibers.

An Overview on the Formation and Processing of Nitrogen-Vacancy Photonic Centers in Diamond by Ion Implantation

Nitrogen-vacancy (NV) in diamond possesses unique properties for the realization of novel quantum devices. Among the possibilities in the solid state, a NV defect center in diamond stands out for its robustness—its quantum state can be initialized, manipulated, and measured with high fidelity at room temperature. In this paper, we illustrated the formation kinetics of NV centers in diamond and their transformation from one charge state to another. The controlled scaling of diamond NV center-based quantum registers relies on the ability to position NV defect centers with high spatial resolution. Ion irradiation technique is widely used to control the spatial distribution of NV defect centers in diamond. This is addressed in terms of energetics and kinetics in this paper. We also highlighted important factors, such as ion struggling, ion channeling, and surface charging, etc. These factors should be considered while implanting energetic nitrogen ions on diamond. Based on observations of the microscopic structure after implantation, we further discussed post-annealing treatment to heal the damage produced during the ion irradiation process. This article shows that the ion implantation technique can be used more efficiently for controlled and efficient generation of NV color centers in diamond, which will open up new possibilities in the field of novel electronics and computational engineering, including the art of quantum cryptography, data science, and spintronics.

Transient absorption in pumped Yb fibers opens a path to photodarkening

We investigated the strong absorption change appearing in ytterbium (Yb)-doped silica simultaneously with Yb3+ excitation and vanishing immediately after pump power switch-off. The transient absorption peaks below 300 nm for all the investigated host glass compositions. It extends at least to 500 nm for samples with aluminum codoping or without any codoping and is therefore supposed to constitute the first step needed to enable photodarkening (PD). Our observations indicate that defect complexes including one Yb3+ ion can be activated stepwise. Firstly, their original absorption spectrum is shifted by the energy of the Yb3+ excitation. Secondly, this transient absorption opens the path to the generation of PD color centers by pump photons or energy transfer from neighboring excited Yb3+ ions. In samples codoped with phosphorous only, we found transient absorption of comparable strength but limited to the wavelength range below 350 nm. Thus, the second step of activation seems to be inhibited, which might be an explanation for the consistently observed low PD effects in this fiber type.

Generation of color centers when annealing LiF crystals irradiated by Kr ions with an energy of 150 MeV

The effect thermal annealing has on F and Fn centers in LiF crystals irradiated by Kr ions with an energy of 150 MeV is studied with allowance for fluence and ionic currents. It is found that annealing at a temperature of 400 K using crystals irradiated at a fluence of ≥1013 iom/cm2 reduces the concentration of F centers (due to annihilation with H centers) and raises the concentration of complex Fn centers.