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Mechanoluminescence (ML) phosphors have found various promising utilizations such as in non-destructive stress sensing, anti-counterfeiting, and bio stress imaging. However, the reported NIR MLs have predominantly been limited to bulky particle size and weak ML intensity, hindering the further practical applications. For this regard, a nano-sized ZnGa2O4: Cr3+ NIR ML phosphor is synthesized by hydrothermal method. By improving the synthesis method and regulating the chemical composition, the NIR ML (600-1000 nm) intensity of such nano-materials has been further enhanced about four times. The reasons for the ML performance difference between micro-/nano- sized phosphors also have been preliminarily analyzed. Additionally, this work probes into the ML mechanism deeply in traps' aspect from band structure and defect formation energy, which can supply significant references for a new approach to develop efficient NIR ML nanoparticles. Finally, due to excellent tissue penetration capability, nano-sized ZnGa2O4:Cr3+ NIR ML phosphor shows great potential applications in biomedical fields such as for the detection of clinical oral diseases.
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We report on a polarization-resolved study of mid-infrared emission properties of Er3+-doped orthorhombic yttrium aluminum perovskite YAlO3 single crystal. For the 4I11/2 â 4I13/2 Er3+ transition, the stimulated emission cross section is 0.20 × 10-20â cm2 at 2919â nm for light polarization E â c. Pumped by an Yb-fiber laser at 976â nm, the 10â at.% Er:YAlO3 laser delivered 1.36â W at 2919â nm with a slope efficiency of 31.4%, very close to the Stokes limit, a laser threshold as low as 33â mW and a linear polarization. Pump-induced polarization switching between E || b and E || c eigen states was observed and explained by excited-state absorption from the terminal laser level.
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A Tm:LiYF4 laser operating on the 3H4 â 3H5 transition is embedded in a high-power diode-pumped Nd:ASL laser for intracavity upconversion pumping at 1.05â µm. This leads to a record-high output power at 2.3â µm for any bulk thulium laser pumped by an upconversion process. The continuous-wave Tm:LiYF4 laser delivers 1.81â W at 2.3â µm for 32â W of laser-diode pump power, making this kind of pumping competitive with direct diode pumping. The intracavity pumping process allows for counteracting the low absorption inherent to upconversion pumping and to dispatch the thermal loads on two separate laser crystals. The proposed laser architecture also features a relatively weak heating of the Tm:LiYF4 crystal and an increased tolerance to Tm3+ absorption. This laser design opens a new paradigm that holds great promise for high-power 2.3-µm solid-state lasers based on thulium ions.
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The green-emitting SrAl2O4:Eu,Dy phosphor is the most widely used and well-studied persistent luminescent phosphor available today. Recent efforts to boost its performance in terms of luminescence intensity and duration are challenged by complex loss mechanisms, including the optically stimulated release of previously trapped charges by excitation light. Here, we present minimally scattering SrAl2O4:Eu,Dy single crystals, which, as opposed to powder phosphors, allow to profit from a so-called volume effect, resulting in a significantly increased emission intensity. Additionally, they allow for the identification of the reabsorption of the afterglow emission by trapped charges as an important loss mechanism, leading to a nonlinear scaling of the emission intensity with the crystal size. If circumvented, the emission intensity could be further increased, in persistent luminescent powders, ceramics, and single crystals.
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Biomedical photothermal therapy with optical nanoparticles is based on the conversion of optical energy into heat through three steps: optical absorption, thermal conversion of the absorbed energy and heat transfer to the surrounding medium. The light-to-heat conversion efficiency (LHCE) has become one of the main metrics to quantitatively characterize the last two steps and evaluate the merit of nanoparticules for photothermal therapy. The estimation of the LHCE is mostly performed by monitoring the temperature evolution of a solution under laser irradiation. However, this estimation strongly depends on the experimental set-up and the heat balance model used. We demonstrate here, theoretically and experimentally, that the LHCE at multiple wavelengths can be efficiently and directly determined, without the use of models, by calibrated photoacoustic spectroscopy. The method was validated using already characterized colloidal suspensions of silver sulfide nanoparticles and maghemite nanoflowers and an uncertainty of 3 to 7% was estimated for the LHCE determination. Photoacoustic spectroscopy provides a new, precise and robust method of analysis of the photothermal capabilities of aqueous solutions of nanoagents.
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Persistent luminescence nanoparticles (PLNPs) are innovative materials able to emit light for a long time after the end of their excitation. Thanks to this property, their detection can be separated in time from the excitation, making it possible to obtain images with a high signal-to-noise ratio. This optical property can be of particular interest for the development of in vitro biosensors. Here, we report the unexpected effect of hydrogen peroxide (H2 O2 ) on the signal intensity of ZnGa2 O4 :Cr3+ (ZGO) nanoparticles. In the presence of H2 O2 , the signal intensity of ZGO can be amplified. This signal amplification can be used to detect and quantify H2 O2 in various media, using non-functionalized ZGO nanoparticles. This small molecule can be produced by several oxidases when they react with their substrate. Indeed, the quantification of glucose, lactic acid, and uric acid is possible. The limit of detection could be lowered by modifying the nanoparticles synthesis route. These optimized nanoparticles can also be used as new biosensor to detect larger molecules such as antigen, using the appropriate antibody. This unique property, i.e., persistent luminescence signal enhancement induced by H2 O2 , represents a new way to detect biomolecules which could lead to a very large number of bioassay applications.
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Técnicas Biossensoriais , Nanopartículas , Luminescência , Nanopartículas/química , Técnicas Biossensoriais/métodosRESUMO
Near-infrared (NIR) persistent luminescence (PersL) materials have demonstrated promising developments for applications in many advanced fields due to their unique optical properties. Both high-temperature solid-state (SS) or hydrothermal (HT) methods can successfully be used to prepare PersL materials. In this work, Zn1.33Ga1.34Sn0.33O4:0.5%Cr3+ (ZGSO:0.5%Cr3+), a newly proposed nanomaterial for bioimaging, was prepared using SS and HT methods. The results show the crystal structure, morphology and optical properties of the samples that were prepared using both methods. Briefly, the crystallite size of the ZGSO:0.5%Cr3+ prepared using the SS method is ~3 µm, and as expected, is larger than materials prepared using the HT method. However, the growth process used in the hydrothermal environment promotes the formation of ZGSO:0.5%Cr3+ with more uniform shapes and smaller sizes (less than 500 nm). Different diameter ranges of nanoparticles were obtained using HT and ball milling (BM) methods (ranging from 25-50 nm) and by using SS and BM methods (25-200 nm) as well. In addition, the SS-prepared microstructure material has stronger PersL than HT-prepared particles before they go through ball milling to create nanomaterials. On the contrary, after BM treatment, ZGSO:0.5%Cr3+ HT and BM NPs present higher PersL and photoluminescence (PL) properties than ZGSO:0.5%Cr3+ SS and BM NPs, even though both kinds of NPs present worse PersL and PL compared to the original particles before BM. To summarize: preparation methods, whether by SS or HT, with additional grinding as a second step, can have a significant impact on the morphological and luminescent features of ZGSO:0.5%Cr3+ PersL materials.
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We report on the first laser operation of a disordered Tm:CaGdAlO4 crystal on the 3H4 â 3H5 transition. Under direct pumping at 0.79 µm, it generates 264â mW at 2.32â µm with a slope efficiency of 13.9% and 22.5% vs. incident and absorbed pump power, respectively, and a linear polarization (σ). Two strategies to overcome the bottleneck effect of the metastable 3F4 Tm3+ state leading to the ground-state bleaching are exploited: cascade lasing on the 3H4 â 3H5 and 3F4 â 3H6 transitions and dual-wavelength pumping at 0.79 and 1.05 µm combining the direct and upconversion pumping schemes. The cascade Tm-laser generates a maximum output power of 585â mW at 1.77â µm (3F4 â 3H6) and 2.32â µm (3H4 â 3H5) with a higher slope efficiency of 28.3% and a lower laser threshold of 1.43 W, out of which 332â mW are achieved at 2.32â µm. Under dual-wavelength pumping, further power scaling to 357â mW at at 2.32â µm is observed at the expense of increased laser threshold. To support the upconversion pumping experiment, excited-state absorption spectra of Tm3+ ions for the 3F4 â 3F2,3 and 3F4 â 3H4 transitions are measured for polarized light. Tm3+ ions in CaGdAlO4 exhibit broadband emission at 2.3 - 2.5 µm making this crystal promising for ultrashort pulse generation.
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Cerium-doped lutetium-yttrium oxyorthosilicate (Ce:LYSO) is a well-known single crystal scintillator used in medical imaging and security scanners. Recent development of high power UV LED, matching its absorption band, questions the possibility to use Ce:LYSO in a new way: as LED-pumped solid-state light source. Since Ce:LYSO is available in large size crystals, we investigate its potential as a luminescent concentrator. This paper reports an extensive study of the performance in close relation to the spectroscopic properties of this crystal. It gives the reasons why the Ce:LYSO crystal tested in this study is less efficient than Ce:YAG for luminescent concentration: limited quantum efficiency and high losses coming from self-absorption and from excited-state absorption are playing key roles. However, we demonstrate that a Ce:LYSO luminescent concentrator is an innovative source for solid-state lighting. Pumped by a peak power of 3400 W in quasi-continuous wave regime (40 µs, 10 Hz), a rectangular (1 × 22 × 105 mm3) Ce:LYSO crystal delivers a broadband spectrum (60 nm FWHM) centered at 430 nm. At full output aperture (20 × 1 mm2), it emits a peak power of 116 W. On a squared output surface (1 × 1 mm2) it emits 16 W corresponding to a brightness of 509 W cm-2 sr-1. This combination of spectrum power and brightness is higher than blue LEDs and opens perspectives for Ce:LYSO in the field of illumination namely for imaging.
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Mixed-anion compounds widen the chemical space of attainable materials compared to single anionic compounds, but the exploration of their structural diversity is limited by common synthetic paths. Especially, oxychlorides rely mainly on layered structures, which suffer from low stability during photo(electro)catalytic processes. Herein we report a strategy to design a new polar 3D tetrahedral framework with composition Zn4 Si2 O7 Cl2 . We use a molten salt medium to enable low temperature crystallization of nanowires of this new compound, by relying on tetrahedral building units present in the melt to build the connectivity of the oxychloride. These units are combined with silicon-based connectors from a non-oxidic Zintl phase to enable precise tuning of the oxygen content. This structure brings high chemical and thermal stability, as well as strongly anisotropic hole mobility along the polar axis. These features, associated with the ability to adjust the transport properties by doping, enable to tune water splitting properties for photoelectrocatalytic H2 evolution and water oxidation. This work then paves the way to a new family of mixed-anion solids.
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Nanoestruturas , Cloreto de Sódio/química , Ânions/química , Nanoestruturas/química , Zinco/química , Dióxido de Silício/química , Cloretos/química , Catálise , Eletroquímica/métodosRESUMO
The property of persistent luminescence shows great potential for anti-counterfeiting technology and imaging by taking advantage of a background-free signal. Current anti-counterfeiting technologies face the challenge of low security and the inconvenience of being limited to visible light emission, as emitters in the NIR optical windows are required for such applications. Here, we report the preparation of a series of Zn1+xGa2-2xSnxO4 nanoparticles (ZGSO NPs) with persistent luminescence in the first and second near-infrared window to overcome these challenges. ZGSO NPs, doped with transition-metal (Cr3+ and/or Ni2+) and in some cases co-doped with rare-earth (Er3+) ions, were successfully prepared using an improved solid-state method with a subsequent milling process to reach sub-200 nm size particles. X-ray diffraction and absorption spectroscopy were used for the analysis of the structure and local crystal field around the dopant ions at different Sn4+/Ga3+ ratios. The size of the NPs was ~150 nm, measured by DLS. Doped ZGSO NPs exhibited intense photoluminescence in the range from red, NIR-I to NIR-II, and even NIR-III, under UV radiation, and showed persistent luminescence at 700 nm (NIR-I) and 1300 nm (NIR-II) after excitation removal. Hence, these NPs were evaluated for multi-level anti-counterfeiting technology.
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Fast detection of hydrogen gas leakage or its release in different environments, especially in large electric vehicle batteries, is a major challenge for sensing applications. In this study, the morphological, structural, chemical, optical, and electronic characterizations of ZnO:Eu nanowire arrays are reported and discussed in detail. In particular, the influence of different Eu concentrations during electrochemical deposition was investigated together with the sensing properties and mechanism. Surprisingly, by using only 10 µM Eu ions during deposition, the value of the gas response increased by a factor of nearly 130 compared to an undoped ZnO nanowire and we found an H2 gas response of â¼7860 for a single ZnO:Eu nanowire device. Further, the synthesized nanowire sensors were tested with ultraviolet (UV) light and a range of test gases, showing a UV responsiveness of â¼12.8 and a good selectivity to 100 ppm H2 gas. A dual-mode nanosensor is shown to detect UV/H2 gas simultaneously for selective detection of H2 during UV irradiation and its effect on the sensing mechanism. The nanowire sensing approach here demonstrates the feasibility of using such small devices to detect hydrogen leaks in harsh, small-scale environments, for example, stacked battery packs in mobile applications. In addition, the results obtained are supported through density functional theory-based simulations, which highlight the importance of rare earth nanoparticles on the oxide surface for improved sensitivity and selectivity of gas sensors, even at room temperature, thereby allowing, for instance, lower power consumption and denser deployment.
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Functional colloidal nanoparticles capable of converting between various energy types are finding an increasing number of applications. One of the relevant examples concerns light-to-heat-converting colloidal nanoparticles that may be useful for localized photothermal therapy of cancers. Unfortunately, quantitative comparison and ranking of nanoheaters are not straightforward as materials of different compositions and structures have different photophysical and chemical properties and may interact differently with the biological environment. In terms of photophysical properties, the most relevant information to rank these nanoheaters is the light-to-heat conversion efficiency, which, along with information on the absorption capacity of the material, can be used to directly compare materials. In this work, we evaluate the light-to-heat conversion properties of 17 different nanoheaters belonging to different groups (plasmonic, semiconductor, lanthanide-doped nanocrystals, carbon nanocrystals, and metal oxides). We conclude that the light-to-heat conversion efficiency alone is not meaningful enough as many materials have similar conversion efficienciesâin the range of 80-99%âwhile they significantly differ in their extinction coefficient. We therefore constructed their qualitative ranking based on the external conversion efficiency, which takes into account the conventionally defined light-to-heat conversion efficiency and its absorption capacity. This ranking demonstrated the differences between the samples more meaningfully. Among the studied systems, the top-ranking materials were black porous silicon and CuS nanocrystals. These results allow us to select the most favorable materials for photo-based theranostics and set a new standard in the characterization of nanoheaters.
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Trivalent lanthanides in wide bandgap fluoride or phosphate hosts can present persistent luminescence between 200 nm and 1.7 µm after charging by X-rays. Mechanisms are reviewed and applications envisioned.
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Mid-infrared Er:CaF2 laser operating on the 4I11/2 â 4I13/2 transition is developed. Its power scaling capabilities and thermo-optics (fractional heat loading and thermal lensing) are compared under pumping into the 4I11/2 and 4I9/2 states. Using a 4.5 at.% Er:CaF2 crystal, a record-high continuous-wave output power of 0.83 W is achieved at 2800â nm with a slope efficiency of 31.6% and a laser threshold of 24â mW and the fractional heat loading is measured under lasing and non-lasing conditions, yielding the values of 52.0% and 71.7%, respectively (for pumping at 967.6 nm, into the 4I11/2 state). The thermal lens in Er:CaF2 is negative (divergent) owing to the negative thermo-optic coefficient and large and negative contribution of the photo-elastic effect. The sensitivity factors of the thermal lens are Mr = -4.84 and Mθ = -5.15 [m-1/(kW/cm2)] and the astigmatism degree is as low as 6%. When pumping into the higher lying 4I9/2 manifold, the thermal lens is enhanced owing to the additional heat generation from the multiphonon non-radiative path from this state, and the laser slope efficiency is deteriorated.
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This article reports for the first time an in-depth ab initio computational study on intrinsic point defects in Sr4Al14O25 that serves as host lattice for numerous phosphors. Defect Formation Enthalpies (DFEs) and defect concentrations were computed considering the supercell approach for different oxygen atmospheres. The charge transition levels have been determined for several point defects in their thermodynamically stable state and their impact on the electronic structure of the ideal unfaulted material is discussed. Our simulations demonstrated that the formation of most of native point defects is energy intensive under oxygen-rich, -intermediate or -poor synthesis conditions, except for the oxygen vacancies under O-poor atmosphere.
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Purpose: The purpose of this study was to evaluate the effects of anodal tDCS applied over the dorsolateral prefrontal cortex (DLPFC) on muscle endurance in the back-squat exercise. Methods: Eleven healthy males, intermediate in resistance training (RT), aged between 18 and 31 years (25.5 ± 4.4 years) were recruited. In the initial visits (1st and 2nd visits), participants performed a 1RM test to determine the load in the back-squat exercise. Following the two initials visits, participants attended the lab for the two experimental conditions (anodal tDCS and sham), which were completed a week apart, with sessions randomly counterbalanced. The stimulation was applied over the DLPFC for 20 minutes using a 2 mA current intensity. Immediately after the experimental conditions, participants completed three sets of maximum repetitions (80% of 1RM), with a 1-minute recovery interval between each set in the back-squat exercise. Muscle endurance was determined by the total number of repetitions and the number of repetitions in each set. Results: The total number of repetitions was higher in the anodal tDCS condition compared to sham condition (p ≤ .0001). Moreover, the number of repetitions performed in the first set was higher for anodal tDCS condition than in the sham condition (p ≤ .01). Conclusion: This study found improvement in back-squat exercise performance after the application of anodal tDCS. The effects of anodal tDCS applied over DLPFC may be a promising ergogenic resource on muscle endurance in the back-squat exercise.
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Treinamento Resistido , Estimulação Transcraniana por Corrente Contínua , Adolescente , Adulto , Humanos , Masculino , Postura , Córtex Pré-Frontal/fisiologia , Adulto JovemRESUMO
This study provided a proof-of-concept and test-retest reliability of measures frequently used to assess a mental fatigue paradigm. After familiarization, 28 healthy men performed (40-min) the Rapid Visual Information Processing (RVP) test in a test-retest design, having mental fatigue sensation, motivation, emotional arousal, total mood disturbance, and electroencephalography (EEG) in the prefrontal cortex measured before and after the test. EEG was recorded during a 3-min rest so that the power spectral density of theta (3-7 Hz) and alpha (8-13 Hz) bands was calculated. Pre-to-post RVP test changes in psychological and physiological domains were compared (paired-T tests), and absolute (standard error of measurement (SEM) and minimal difference (MD)) and relative reliability (intraclass correlation coefficient (ICC)) were calculated. The RVP test induced an increase (p < 0.05) in mental fatigue sensation (120.9% (109.4; 132.4)) and total mood disturbance (3.5% (-6.3; 13.3)), and a decrease in motivation (-7.1% (-9.2; -5.1)) and emotional arousal (-16.2% (-19.1; -13.2)). Likewise, EEG theta (59.1% (33.2; 85.0); p < 0.05), but not alpha band, increased due to RVP test. All psychophysiological responses showed poor-to-moderate relative reliability. Changes in mental fatigue sensation and motivation were higher than SEM and MD, but changes in EEG theta band were higher only than SEM. Mental fatigue sensation, motivation, and EEG theta band were sensitive to distinguish a mental fatigue paradigm despite true mental fatigue effects on theta activity may be trivial.
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Eletroencefalografia , Fadiga Mental , Humanos , Masculino , Motivação , Reprodutibilidade dos Testes , DescansoRESUMO
A comparative investigation of the post-electroplating treatment influence on the gas detecting performances of single ZnO nanorod/nanowire (NR/NW), as grown by electrochemical deposition (ECD) and integrated into nanosensor devices, is presented. In this work, hydrothermal treatment (HT) in a H2O steam and conventional thermal annealing (CTA) in a furnace at 150 °C in ambient were used as post-growth treatments to improve the material properties. Herein, the morphological, optical, chemical, structural, vibrational, and gas sensing performances of the as-electrodeposited and treated specimens are investigated and presented in detail. By varying the growth temperature and type of post-growth treatment, the morphology is maintained, whereas the optical and structural properties show increased sample crystallization. It is shown that HT in H2O vapors affects the optical and vibrational properties of the material. After investigation of nanodevices based on single ZnO NR/NWs, it was observed that higher temperature during the synthesis results in a higher gas response to H2 gas within the investigated operating temperature range from 25 to 150 °C. CTA and HT or autoclave treatment showed the capability of a further increase in gas response of the prepared sensors by a factor of â¼8. Density functional theory calculations reveal structural and electronic band changes in ZnO surfaces as a result of strong interaction with H2 gas molecules. Our results demonstrate that high-performance devices can be obtained with high-crystallinity NWs/NRs after HT. The obtained devices could be the key element for flexible nanoelectronics and wearable electronics and have attracted great interest due to their unique specifications.