Band Intensity Ratio Research Articles

Influence of Synthesis Parameters on Structure and Characteristics of the Graphene Grown Using PECVD on Sapphire Substrate.

The high surface area and transfer-less growth of graphene on dielectric materials is still a challenge in the production of novel sensing devices. We demonstrate a novel approach to graphene synthesis on a C-plane sapphire substrate, involving the microwave plasma-enhanced chemical vapor deposition (MW-PECVD) technique. The decomposition of methane, which is used as a precursor gas, is achieved without the need for remote plasma. Raman spectroscopy, atomic force microscopy and resistance characteristic measurements were performed to investigate the potential of graphene for use in sensing applications. We show that the thickness and quality of graphene film greatly depend on the CH4/H2 flow ratio, as well as on chamber pressure during the synthesis. By varying these parameters, the intensity ratio of Raman D and G bands of graphene varied between ~1 and ~4, while the 2D to G band intensity ratio was found to be 0.05-0.5. Boundary defects are the most prominent defect type in PECVD graphene, giving it a grainy texture. Despite this, the samples exhibited sheet resistance values as low as 1.87 kΩ/□. This reveals great potential for PECVD methods and could contribute toward efficient and straightforward graphene growth on various substrates.

Ultrasensitive and Adjustable Nanothermometers Based on Er3+-Sensitized Core@Shell Nanoparticles for Use in the First Biological Window.

In recent years, intensive research has focused on lanthanide-doped nanoparticles (NPs) used as noncontact temperature sensors, particularly in nanomedicine. These NPs must be capable of excitation and emission within biological windows, where biological materials usually show better transparency for radiation. In this article, we propose that NPs sensitized with Er3+ ions can be applied as temperature sensors in biological materials. We synthesized the NPs through a reaction in high-boiling solvents and confirmed their crystal structure and the formation of core@shell NPs by using X-ray diffraction, high-resolution transmission electron microscopy, and element distribution mapping within the NPs. NaErF4@NaYF4, NaYF4:12.5% Er3+, 2.5% Tm3+@NaYF4, NaYF4:7.5% Er3+@NaYF4, and NaYF4:12.5% Er3+, 2.5% Ho3+@NaYF4 exhibited intense upconversion (UC) emission under 1532 nm laser excitation detectable also in the whole human blood. We propose that this UC results from energy transfer between Er3+ ions and from Er3+ to Tm3+ or Ho3+ codopants. To determine the mechanism of UC, we measured the dependence of the emission band intensities on the laser power densities. Importantly, we also analyzed the temperature-dependent emission of the NPs within the 295-360 K range. Based on the collected emission spectra, we calculated the luminescence intensity ratios (LIRs) of the emission bands to assess their potential for optical temperature sensing. The temperature-sensing properties varied with the concentration of Er3+ ions and the presence of additional Tm3+ or Ho3+ codopants. Depending on the NP composition and the emission bands used for luminescence ratio calculations, the maximum relative temperature sensitivity ranged from 4.55%·K-1 to 1.12%·K-1, with temperature resolution between 0.05 and 2.53 K at room temperature. Finally, as proof of using NPs as temperature sensors in biomedicine, we successfully measured the temperature-dependent emission of NaYF4:7.5% Er3+@NaYF4 NPs dispersed in whole blood under 1532 nm excitation. We demonstrated that the ratio of Er3+ ion emission bands changes with temperature, indicating that these NPs have potential applications in temperature sensing within biological environments. We also confirmed the properties of NPs as temperature sensors by measuring the temperature reading uncertainty and the repeatability of the LIR readings during heating-cooling cycles, thereby confirming the excellent properties of the studied systems as temperature sensors.

Synthesis and structural analysis of graphene nanosheets via microwave atmospheric pressure plasma

This study reports the effective synthesis of multilayered graphene sheets via microwave atmospheric pressure plasma. This innovative approach streamlines and expedites graphene production and other carbon nanostructures, eliminating the need for catalysts, solvents, or complex processing conditions. Ethanol is directly injected into a microwave-generated argon plasma plume, leading to the formation of graphene. Raman spectroscopy revealed characteristic peaks (2D, G, and D bands) confirming graphene composition, with defects indicated by the D band. X-ray diffraction analysis supported these findings, indicating a broad peak at 25∘ corresponding to the (002) plane, affirming a multi-layered graphene structure. Scanning electron microscopy exhibited crumpled, randomly oriented graphene sheets, albeit with uneven structures suggesting impurity incorporation. The presence of defects was quantified through the intensity ratio of the D to G band (ID/IG) in Raman spectroscopy, revealing a value of 0.80, signifying the presence of defects in the synthesized graphene. The 2D to G band intensity ratio (I2D/IG) suggested the existence of 7–10 graphene layers, highlighting the need for further optimization for enhanced graphene quality and purity.

Temperature Dependent near Infrared Spectroscopy of Electron Irradiated Ceria Single Crystals.

The FTIR absorption bands of virgin and electron-irradiated CeO2 single crystals were measured from 20 K to 500 K between 4000 cm-1 and 12,000 cm-1 (~830 nm to 2500 nm). Three broad bands centered at about 6100 cm-1 (~0.75 eV), 7000 cm-1 (~0.87 eV), and 10,500 cm-1 (~1.3 eV) were recorded above 100 K for the 2.5 MeV electron energy. Two smaller bands at about 4300 cm-1 (~0.53 eV) and 5500 cm-1 (~0.68 eV) were also recorded below 100 K. Similar broad bands centered at about 4100 cm-1 (~0.52 eV), 6400 cm-1 (~0.79 eV), 7600 cm-1 (~0.94 eV), and 10,500 cm-1 (~1.3 eV) are also found for the 1.4 MeV electron energy above 300 K. The evolution of these absorption bands was followed as a function of temperature. The plots of band intensity ratios show a thermally activated process corresponding to the ionization of the deep electronic levels of point defects in the band gap of ceria of ~26,000 cm-1 (~3.2 eV). These five bands are assigned to the different charge states (0, -1, -2, -3, -4) of the Ce vacancies produced by elastic collisions above 1.0 MeV.

Regulating the luminescence properties of Eu2W3O12 red-emitting phosphor via rare-earth ions doping for optical thermometry, white light-emitting diode and plant growth applications

To fulfil various applications, series of rare-earth (RE) ions (i.e., La3+, Gd3+, Sm3+) doped Eu2W3O12 (EWO) phosphors were synthesized. All the designed phosphors can emit glaring visible lights from Eu3+ and their fluorescence intensities were significantly enhanced through RE ions doping. To explore the impact of RE ions doping on the symmetric properties of Eu3+ in studied samples, theoretical calculation based on Judd-Ofelt theory was performed. Moreover, through utilizing temperature-related emission spectra, the thermal quenching behaviors of resultant phosphors were studied and found that their thermal stability had been improved by adding RE ions. Furthermore, the thermometric properties of designed phosphors were examined through adopting the single-band ratiometric technique to analyzing the temperature-dependent fluorescence intensity ratio of the emission band arising from 5D0 → 7F2 transition of Eu3+. It is found that maximum absolute and relative sensitivities of resulting phosphors were 0.197 and 1.202 % K−1, respectively. Additionally, two types of devices, i.e., white light-emitting diode (white-LED) and red-emitting LED, where the prepared phosphors play as red-emitting components, were fabricated. The packaged white-LEDs can emit warm white light with high color rendering index and low correlated color temperature, which are insensitive to operating current. Considering the red-emitting LEDs, their emission bands overlap with the absorption bands of plant pigments, which can promote plant growth and it was verified by peppermint growth experiments. These results verify that the introduction of RE ions is a feasible approach to modify the luminescence performances of phosphors to realize diversified applications.

The impact of high pressure on the number of photons involved in upconversion luminescence of NaYF4:Er3+@NaYF4 and NaYF4:Yb3+,Er3+@NaYF4 core@shell nanoparticles and application as contactless pressure sensor

Inorganic nanomaterials doped with lanthanide ions and exhibiting upconversion (UC) luminescence are leading in research of nonlinear optical materials. Extreme conditions, such as high-pressure compression (in the GPa range), may influence the physicochemical properties of various compounds. In this work, we investigated the optical properties of upconverting NaYF4:Er3+@NaYF4 and NaYF4:Yb3+,Er3+@NaYF4 core@shell nanoparticles (NPs), focusing on the impact of high pressure on the number of photons involved in the UC mechanism. We measured the UC emission spectra of the synthesized NPs under high-pressure conditions, which allowed us to observe the pressure-induced intensity changes, band centroids spectral shifts, and band intensity ratios alterations. Importantly, by measuring the power-dependent UC emission spectra as a function of pressure, we determined and analyzed the number of photons (n) involved in the UC processes for the first time. It turned out that the n value changes with pressure as a result of diverse multi-phonon relaxation processes enhanced under high-pressure conditions. The results show potential adjustment of UC mechanisms with the use of high-pressure. The calculated band intensity ratios were also used for pressure sensing applications, resulting in the relative sensitivity reaching almost ≈20 % GPa−1 for the Er3+-doped core@shell NPs.

Deep postnatal phenotyping of a new mouse model of nonketotic hyperglycinemia.

Nonketotic hyperglycinemia due to deficient glycine cleavage enzyme activity causes a severe neonatal epileptic encephalopathy. Current therapies based on mitigating glycine excess have only limited impact. An animal model with postnatal phenotyping is needed to explore new therapeutic approaches. We developed a Gldc p.Ala394Val mutant model and bred it to congenic status in two colonies on C57Bl/6J (B6) and J129X1/SvJ (J129) backgrounds. Mutant mice had reduced P-protein and enzyme activity indicating a hypomorphic mutant. Glycine levels were increased in blood and brain regions, exacerbated by dietary glycine, with higher levels in female than male J129 mice. Birth defects were more prevalent in mutant B6 than J129 mice, and hydrocephalus was more frequent in B6 (40%) compared to J129 (none). The hydrocephalus rate was increased by postnatal glycine challenge in B6 mice, more so when delivered from the first neonatal week than from the fourth. Mutant mice had reduced weight gain following weaning until the eighth postnatal week, which was exacerbated by glycine loading. The electrographic spike rate was increased in mutant mice following glycine loading, but no seizures were observed. The alpha/delta band intensity ratio was decreased in the left cortex in female J129 mice, which were less active in an open field test and explored less in a Y-maze, suggesting an encephalopathic effect. Mutant mice showed no evidence of memory dysfunction. This partial recapitulation of human symptoms and biochemistry will facilitate the evaluation of new therapeutic approaches with an early postnatal time window likely most effective.

Role of Polycyclic Aromatic Hydrocarbons with Edge Defects in Explaining Astronomical Infrared Emission Observations

A systematic study was performed on the spectral properties of polycyclic aromatic hydrocarbons (PAHs) with edge defects using harmonic density functional theory calculations. Their potential astronomical relevance was assessed through direct comparison with NIRSpec and MIRI-MRS spectra of the atomic photodissociation region of the Orion Bar from the JWST Early Release Science PDRs4All program. It is found that the astronomical 6.2 μm PAH emission band, including its blue side, is well reproduced by PAHs with edge defects, when taking into account the effects of polarization in the computations, and without a need for PAHs that contain nitrogen. Small neutral PAHs with edge defects explain the blue wing of the 3.3 μm band. A low number of edge defects is required to reproduce the 8.6 and 11.2 μm band profiles, while the 11.0 + 11.2/12.7 μm band intensity ratio is a measure for the number of edge defects. A blind database fit to the Orion Bar spectrum reproduces the 6–15 μm region with an error of 9.9% and shows a clear delineation of charge, with the 6–10 μm PAH bands being carried by PAH cations and the 10–15 μm region by predominantly neutral PAHs. The contribution of anions is negligible. Armchair PAHs fit the 12.7 μm band, simultaneously producing a very weak broad emission feature centered at 3.225 μm. Zigzag PAHs fit the 11.2 μm band. It is concluded that PAHs with a low number of edge defects, in addition to armchair and zigzag PAHs, all contribute to the observed interstellar infrared emission.

Simple and sensitive galactose monitoring based on capillary SERS sensor.

Galactosemia, a severe genetic metabolic disorder, results from the absence of galactose-degrading enzymes, leading to harmful galactose accumulation. In this study, we introduce a novel capillary-based surface-enhanced Raman spectroscopy (SERS) sensor for convenient and sensitive galactose detection. The developed sensor enhances SERS signals by introducing gold nanoparticles (Au NPs) onto the surface of silver nanoshells (Ag NSs) within a capillary, creating Ag NSs with Au NPs as satellites. Utilizing 4-mercaptophenylboronic acid (4-MPBA) as a Raman reporter molecule, the detection method relies on the conversion of 4-MPBA to 4-mercaptophenol (4-MPhOH) driven by hydrogen peroxide (H2O2) generated during galactose oxidation by galactose oxidase (GOx). A new SERS signal was observed, which was generated by H2O2 produced when galactose and GOx reacted. Our strategy yielded a quantitative change in the SERS signal, specifically in the band intensity ratio of 998 to 1076 cm-1 (I998/I1076) as the galactose concentration increased. Our capillary-based SERS biosensor provides a promising platform for early galactosemia diagnosis.

Raman Imaging-A Valuable Tool for Tracking Fatty Acid Metabolism-Normal and Cancer Human Colon Single-Cell Study.

Altered metabolism of lipids is a key factor in many diseases including cancer. Therefore, investigations into the impact of unsaturated and saturated fatty acids (FAs) on human body homeostasis are crucial for understanding the development of lifestyle diseases. In this paper, we focus on the impact of palmitic (PA), linoleic (LA), and eicosapentaenoic (EPA) acids on human colon normal (CCD-18 Co) and cancer (Caco-2) single cells using Raman imaging and spectroscopy. The label-free nature of Raman imaging allowed us to evaluate FAs dynamics without modifying endogenous cellular metabolism. Thanks to the ability of Raman imaging to visualize single-cell substructures, we have analyzed the changes in chemical composition of endoplasmic reticulum (ER), mitochondria, lipid droplets (LDs), and nucleus upon FA supplementation. Analysis of Raman band intensity ratios typical for lipids, proteins, and nucleic acids (I1656/I1444, I1444/I1256, I1444/I750, I1304/I1256) proved that, using Raman mapping, we can observe the metabolic pathways of FAs in ER, which is responsible for the uptake of exogenous FAs, de novo synthesis, elongation, and desaturation of FAs, in mitochondria responsible for energy production via FA oxidation, in LDs specialized in cellular fat storage, and in the nucleus, where FAs are transported via fatty-acid-binding proteins, biomarkers of human colon cancerogenesis. Analysis for membranes showed that the uptake of FAs effectively changed the chemical composition of this organelle, and the strongest effect was noticed for LA. The spectroscopy studies have been completed using XTT tests, which showed that the addition of LA or EPA for Caco-2 cells decreases their viability with a stronger effect observed for LA and the opposite effect observed for PA. For normal cells, CCD-18 Co supplementation using LA or EPA stimulated cells for growing, while PA had the opposite impact.

Revealing the Pressure-Induced Phase Transformation of Xenotime TbPO4 via In Situ Photoluminescence Spectroscopy.

The pressure-induced phase transformations of certain rare earth (RE) orthophosphates have attracted broad interest from geoscience to structural ceramics. Studying these transformations has required in situ Raman spectroscopy or synchrotron X-ray diffraction (XRD), each of which suffers from poor signal or limited accessibility, respectively. This study exploits the photoluminescence (PL) of Tb3+ ions and the unique sensitivity of PL to the local bonding environment to interrogate the symmetry-reducing xenotime-monazite phase transformation of TbPO4. At pressures consistent with the XRD-based phase transformation onset pressure of 8.7(6) GPa, PL spectra show new peaks emerging as well as trend changes in the centroids and intensity ratios of certain PL bands. Furthermore, PL spectra of recovered samples show transformation is irreversible. Hysteresis in certain PL band intensity ratios also reveals the stress history in TbPO4. This in situ PL approach can be applied to probe pressure-induced transformations and crystal field distortions in other RE-based oxide compounds.

Lanthanide-grafted covalent organic framework as a colorimetric and luminescence dual-mode nanoprobe for tetracycline detection

Tetracyclines (TCs) are a group of antibiotics commonly using for infection treatment, however, the leftovers in potable water and food which are derived from the abuse of TCs lead to the adverse human health and environmental impacts. Herein, we developed a lanthanide-grafted covalent organic framework (COF) as a colorimetric and luminescence dual-mode nanoprobe to realize precise, sensitive, rapid, real-time TC determination. Ce3+, Eu3+ ions were chosen to functionalize COFs due to their particular corresponding catalytic and luminescent characteristic for bimodal sensing. COF-Ce-Eu can work as an enzyme mimic to catalytically oxidize the substrate of 3,3′,5,5′-tetramethylbenzidine (TMB) with existence of H2O2, besides, the addition of TC is conducive to promote the pristine catalytic activity as the formation of complexation of COF-Ce-Eu with TC. The catalytic activity and the absorbance of COF-Ce-Eu directly correlate to TC concentration. The ratiometric luminescence response was established on the intensity ratio of the broad band centered at 512 nm originated from the matrix COF and the sharp peak at 616 nm originated from Eu3+. The decrease in luminescence intensity of the peak at 512 nm and the increase at 616 nm depended on TC concentration. This colorimetric and luminescence dual-mode platform exhibits excellent selectivity and sensitivity towards TC, with a wide linear range of 0–50 μM, and low detection limits of 24 nM and 3.4 nM, respectively. The designed bimodal sensing strategy provide a promising double assurance for the accurate trace of TC in food and water samples.

Design guidelines for a high-performance hard carbon anode in sodium ion batteries

A systematic investigation established a significant correlation between the 2D to G band intensity ratio (I2D/IG) in the Raman spectrum and the internal kinetic barrier for sodium-ion transfer, achieving the highest sodium plateau capacity of ∼400 mA h g−1 (A30 sample).

SrAl12O19:Eu,Cr As Luminescence Thermometers

Luminescent nanothermometers offer several approaches to determine the absolute temperature. Mostly, temperature-stimulated changes in the intensity ratio of emission bands, emission kinetics, band/emission line width, or luminescence band/line peak position are explored. The list is longer and is still growing. In our project, the Cr3+, Eu2+-based aluminates materials were designed taking into account the possibility to work as non-contact luminescent thermometers using mentioned above approaches. In Figure 1 the luminescence spectra of SrAl12O19:Eu,Cr phosphor are shown in the temperature range of 15-500 K. The emission comes from both the directly excited ions, Eu2+ and Cr3+. Particularly strong changes with temperature can be seen in the Eu2+ emission around 350 - 470 nm and Cr3+ above 670 nm. Luminescent mechanisms of energy transfer between specific activators of the aluminates lattice will be presented, the consequence of which is obtaining by the material sophisticated thermometric properties in a wide range of measured temperature, from cryogenic to around 500 K. The research finances by the Polish National Science Centre under grant #UMO2018/31/B/ST4/00924 and partially by program “Excellence Initiative – Research University” (IDUB) for years 2020-2026 for University of Wrocław (grant # BPIDUB.4610.678.2021) Figure 1

Characterization of Potential Dependent Fouling of Cu Electrodes during Electrochemical Hydrogenation and Hydrogenolysis of Furfural in Acid

Furfural (FF) is a platform molecule derived from biomass, that can be electrochemically reduced to produce furfuryl alcohol (FA), a furanic polymer intermediate, and 2-methylfuran (MF), a fuel candidate. On Cu in acidic media, it has been shown that FA and MF are produced via parallel reactions as opposed to a series reaction. Our previous work investigated the reactions for FA and MF production electrochemically with FF concentrations between 10 and 120 mM, showing positive order with respect to FF at low concentrations and zero order rates with respect to FF at higher concentrations. This finding suggesting non-competitive Langmuir-Hinshelwood mechanisms at concentrations of FF between 10 and 120 mM in pH 0 and 1 acidic solutions. At 200 mM concentrations of FF, we have identified fouling on the Cu surface. At moderate potentials, the fouling takes the form of a polymer material, whereas at more negative reduction potentials the fouling takes the form of graphitic coking. Understanding how fouling occurs on Cu electrodes is important in achieving progress towards mitigating or reducing the impact of fouling through reactor setup and catalysts design.In this work, conditions that promote fouling were selected so that the fouling of Cu electrodes could be studied. The conditions were chronoamperometry at -560 or -700 mV RHE, 200 mM FF, 0.5M H2SO4, 20:80 vol% acetonitrile:water, for three hours durations. The Cu electrodes were reused for 3 experiments to further promote fouling and study the impact on the electrochemical performance. We showed that after reuse at -560 mV RHE, a polymeric material formed on the Cu electrode, while when reused at -700 mV RHE the electrode was instead covered in a coke like material. FTIR spectroscopy showed that the polymer formed at -560 mV resembled poly(furfuryl alcohol) while the coking substance showed broad absorbance, expected of coke like materials. To better understand the coke material formed at -700 mV, Raman spectroscopy was used. The material resembled graphitic disorganized carbon, with a D/G band intensity ratio of 0.652.

Orange persistent luminescence of LuBaZn3GaO7: Bi3+ phosphor based on defect induction for optical thermometer and multi-mode anti-counterfeiting

In this study, the Bi3+ doped LuBaZn3GaO7 fluorescent powder was produced using a high-temperature solid-state technique, and its long afterglow luminescence and dynamic anti-counterfeiting capabilities were thoroughly examined. Under the ultraviolet (UV) light excitation, the LuBaZn3GaO7 host exhibits broadband self-activated emission band peak at 594 nm, attributed to the O-vacancies. Upon Bi3+ doping, the phosphor produces a narrow emission band in the 350–450 nm wavelength range, which is caused by the 3P1–1S0 transition of the Bi3+ ions in the Ba2+ site. Remarkably, oxygen vacancy-induced electronic localization around the Bi3+ ions increases the emission intensity of LuBaZn3GaO7:0.01Bi3+ around ten times that of LuBaZn3GaO7 between 450 and 850 nm wavelength. With the variation in excitation light wavelength, the intensity of the two emission bands of LuBaZn3GaO7: Bi3+ changed accordingly, exhibiting multi-color luminescence. While the excitation was removed after 3-min irradiation, LuBaZn3GaO7: Bi3+ phosphors continued to emit for 10 min. Moreover, the phosphor emission has good temperature-sensitive characteristics based on the fluorescence intensity ratio (FIR) of the emission bands of Bi3+ ions and host. Hence, an optical thermometry with high-temperature sensitivity was constructed. Consequently, it can be concluded that fluorescent powder has the potential to be applied in the fields of fluorescence temperature measurement and anti-counterfeiting.

Investigation of the cobalt ions diffusion processes in calcium orthovanadate crystals

In this work, the high-temperature diffusion doping method was used for introduction of active cobalt ions into calcium orthovanadate Ca3(VO4)2crystals. Experimental samples were made from a nominally pure CVO single crystal obtained by the Czochralski method. The high-temperature diffusion conditions have been optimized to obtain doped crystals of optical quality during annealing in open and closed zones. Diffusion coefficients of cobalt ions (D) were calculated for various conditions: annealing time 24 - 48 hours; temperature range 1150-1300°C; diffusants - oxide compounds of calcium, cobalt and vanadium: Co3O4, Ca10Co0.5(VO4)7 and Ca3(VO4)2:2wt.%Co3O4; diffusion direction is parallel or perpendicular to the CVO crystal optical axis. The calculated values of the diffusion coefficient varied between 2.09·10-8—1.58·10-7 cm2/s. The activation energy of the diffusion process was determined to be 2.58±0.5 and 2.63±0.5 eV for the [001] and [100] directions, respectively. The maximum cobalt concentration in doped CVO crystals was 2·1020 cm–3. The absorption spectrum of diffusion-doped Ca3(VO4)2:Co samples demonstrates the presence of absorption bands characteristic for Co2+ and Co3+ ions. It was shown that the intensity ratio of the characteristic absorption bands varies depending on the crystal doping method. The optical anisotropy of the crystal increases with dopant concentration increase.

Impact of e-cigarette liquid on porcine lung tissue - ex vivo confocal Raman micro-spectroscopy study.

Ex vivo porcine lung immersed in e-liquid was investigated in-depth using confocal Raman micro-spectroscopy to assess the e-liquid influence on the lung. It was found that lung-related Raman band intensities at 1002, 1548, 1618 and 1655 cm-1 increased after first and second treatments except the surface, which was attributed to the well-known optical clearing effect due to alveoli filling with e-liquid resulting in light scattering reduction. The autofluorescence enhancement was explained by oxidative stress induced in lung during exposure to e-liquid. Moreover, e-liquid induced collagen dehydration was revealed by the I937 /I926 Raman band intensity ratio change. The effect was enhanced after the second treatment of the same lung tissue that indicates the possibility of multi-step OC treatment. We hypothesize that the nicotine-flavour free e-liquids containing glycerol and propylene glycol could potentially be used in clinical protocols as optical clearing agent for enhanced in-depth Raman-guided bronchoscopy. This article is protected by copyright. All rights reserved.

All Inorganic Sb3+–Ln3+‐Codoped Cs2NaYCl6 for Highly Efficient Single‐Source White‐Light Emission and Ratiometric Optical Thermometer Applications

AbstractSingle‐source white‐light emitters are highlighted with stable color and excellent color rendering ability, which can largely simplify the white‐light‐emitting‐diode (WLED) structure. All‐inorganic and lead‐free double perovskites have attracted extensive research interest and provide versatile doping sites to accommodate the extrinsic multi‐valent ions. Herein, the synthesis and tunable emission of Sb3+–Ln3+‐codoped Cs2NaYCl6 single crystals (SCs) is reported. Particularly, bright white‐light emission with a high photoluminescence quantum yield of 80.5% is yielded in 0.5%Sb3+–2%Tb3+–2%Sm3+‐codoped Cs2NaYCl6 SCs. Steady‐state photoluminescence (PL) and time‐resolved PL spectra are employed to reveal the energy transfer from Sb3+‐induced self‐trapped excitons to Ln3+ ions. Temperature‐dependent PL spectra further demonstrate that the fluorescence intensity ratio of band 657 to band 590 nm is highly dependent on the temperature, and the relative sensitivity reaches a maximum of up to 1.59% K−1 at 260 K. Moreover, the WLED based on 0.5%Sb3+‐2%Tb3+‐2%Sm3+‐codoped Cs2NaYCl6 SCs delivers a higher average color rendering index of 87 than 0.5%Sb3+‐0.8%Tb3+‐2.5%Ho3+‐codoped Cs2NaYCl6 (74.6). The outstanding white‐light‐emission performance together with the high temperature dependence of the fluorescence spectra confers Sb3+–Ln3+‐codoped Cs2NaYCl6 with huge application potential in solid‐state lighting and ratiometric optical thermometry.

Spectroscopic properties of close-to-perfect-monolayer quasi-free-standing epitaxial graphene on 6H[sbnd]SiC(0001)

In this report, we present transfer-free p-type hydrogen-intercalated quasi-free-standing epitaxial Chemical Vapor Deposition graphene on 15-mm × 15-mm semi-insulating vanadium-compensated on-axis 6HSiC(0001), characterized in that its room-temperature direct-current Hall-effect-derived hole mobility μp= 5019 cm2/Vs, and its statistical number of layers (N), as indicated by the relative intensity of the SiC-related Raman-active longitudinal optical A1 mode at 964 cm−1, equals N= 1.05. The distribution of the ellipsometric angle Ψ measured at an angle of incidence of 50° and λ= 490 nm points out to N= 0.97. The close-to-unity value of N implies that the material under study is a close-to-perfect quasi-free-standing monolayer, which is further confirmed by High-Resolution Transmission Electron Microscopy. Therefore, its spectroscopic properties, which include the SiH peak at 2131 cm−1, the histograms of Ψ and Δ, and the Raman G and 2D band positions, widths, and the 2D-to-G band intensity ratios, constitute a valuable reference for this class of materials.