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Near-infrared (NIR) emitting phosphors draw much attention because they show great applicability and development prospects in many fields. Herein, a series of inverse spinel-type structured LiGa5O8 phosphors with a high concentration of Cr3+ activators is reported with a dual emission band covering NIR-I and II regions. Except for strong ionic exchange interactions such as Cr3+-Cr3+ and Cr3+ clusters, an intervalence charge transfer (IVCT) process between aggregated Cr ion pairs is proposed as the mechanism for the ~1210 nm NIR-II emission. Comprehensive structural and luminescence characterization points to IVCT between two Cr3+ being induced by structural distortion and further enhanced by irradiation. Construction of the configurational energy level diagram enabled elucidation of this transition within the IVCT process. Therefore, this work provides insight into the emission mechanism within the high Cr3+ concentration system, revealing a new design strategy for NIR-II emitting phosphors to promote its response.
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In this study, we synthesized a series of Ga1.98-xInxO3:0.02Cr3+ materials with varying x values from 0.0 to 1.0, focusing on their broadband near-infrared emission and photoelectric properties. Interestingly, photocurrent excitation spectra exhibited behavior consistent with the absorption spectra, indicating the promotion of carriers into the band structure by the 4T1, and 4T2 states of Cr3+ ions. This association suggests that photocurrent in this material is influenced not only by valence to conduction band transitions but also by transitions involving Cr3+ dopants. Our investigation of luminescence quenching mechanisms revealed that nonradiative processes were not directly linked to thermally induced relaxation from the excited state 4T2 to the ground state 4A2, as usually suggested in the literature for this type of material. Instead, we linked it to the thermal ionization of Cr3+ ions. Unexpectedly, this process is unrelated to the transfer of electrons from Cr3+ impurities to the conduction band but is associated with the formation of holes in the valence band. This study provided novel evidence of luminescence quenching via the hole-type thermal quenching process in Cr3+-doped oxides, suggesting potential applicability to other transition metal ions and host materials. Finally, we demonstrated the dual-purpose nature of Ga1.98-xInxO3:0.02Cr3+ as a practical emitter for NIR-pc-LEDs and effective photocurrent for UV detectors. This versatility underscores these materials' practicality and broad application potential in optoelectronic devices designed for near-infrared and ultraviolet applications.
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Microplastics (MPs) are plastic particles between 0.1 and 5,000 µm in size that can contaminate food. Unfortunately, to date, little attention has been paid to analyzing the presence of such particles in baby foods. The present study aimed to determine the degree of contamination of infant formula with MPs. A total of thirty products were subjected to analysis. The research methodology used included the isolation of plastic particles, identification and characterization of MPs using advanced microscopic and spectroscopic techniques. Microplastics were detected in all tested samples. The most frequently identified polymers were polyamide, polyethylene, polypropylene, and poly(ethylene terephthalate). The particles exhibited diverse forms, including fibers, fragments, and films, displaying a range of colors such as colorless, black, and brown particles. Furthermore, the daily intake of MPs by children fed exclusively infant formula was estimated to be approximately 49 ± 32 MPs. This poses a potential health risk for the youngest.
Assuntos
Microplásticos , Poluentes Químicos da Água , Criança , Humanos , Microplásticos/análise , Plásticos , Fórmulas Infantis/análise , Poluentes Químicos da Água/análise , Monitoramento AmbientalRESUMO
The growing interest in the use of near-infrared (NIR) radiation for spectroscopy, optical communication, and medical applications spanning both NIR-I (700-900 nm) and NIR-II (900-1700 nm) has driven the need for new NIR light sources. NIR phosphor-converted light-emitting diodes (pc-LEDs) are expected to replace traditional lamps mainly due to their high efficiency and compact design. Broadband NIR phosphors activated by Cr3+ and Cr4+ have attracted significant research interest, offering emission across a wide range from 700 to 1700 nm. In this work, we synthesized a series of Sc2(1-x)Ga2xO3:Cr3+/4+ materials (x = 0-0.2) with broadband NIR-I (Cr3+) and NIR-II (Cr4+) emission. We observed a substantial increase in the intensity of Cr3+ (approximately 77 times) by incorporating Ga3+ ions. Additionally, our investigation revealed that energy transfer occurred between Cr3+ and Cr4+ ions. Configuration diagrams are presented to elucidate the behavior of Cr3+ and Cr4+ ions within the Sc2O3 matrix. We also observed a phase transition at a pressure of 20.2 GPa, resulting in a new unknown phase where Cr3+ luminescence exhibited a high-symmetry environment. Notably, this study presents the pressure-induced shift of NIR Cr4+ luminescence in Sc2(1-x)Ga2xO3:Cr3+/4+. The linear shifts were estimated at 83 ± 3 and 61 ± 6 cm-1/GPa before and after the phase transition. Overall, our findings shed light on the synthesis, luminescent properties, temperature, and high-pressure behavior within the Sc2(1-x)Ga2xO3:Cr3+/4+ materials. This research contributes to the understanding and potential applications of these materials in the development of efficient NIR light sources and other optical devices.
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Cr-doped inorganic materials are pivotal in developing near-infrared optical materials; however, multivalent Cr ions and their respective distribution in the materials remain ambiguous. Herein, a series of Li(Sc1-xInx)O2:Cr phosphors containing both Cr3+/Cr6+ ions are prepared. High-resolution synchrotron X-ray diffraction (XRD) reveals two similar phases in Li(Sc1-xInx)O2. Raman spectra further confirm distinct scattering patterns for the two end-member compositions, corroborating the findings from the synchrotron XRD analysis. Cr K-edge X-ray absorption near-edge structure and extended X-ray absorption fine structure demonstrate that most Cr ions in the as-prepared samples are Cr6+, while Cr3+ becomes dominant after washing with water. Moreover, the source and distribution of Cr3+ and Cr6+ ions in the as-prepared and washed samples are revealed through X-ray fluorescence and X-ray excited optical luminescence techniques, which indicate that Cr6+ ions aggregate within the sample, while Cr3+ ions are evenly distributed. Photoluminescence, decay curves, and line shape analyses are implemented to resolve the electron-lattice interactions, and the corresponding mechanisms are provided to explain the asymmetry between photoluminescence and photoluminescence excitation spectra. Overall, this study provides valuable insights into the distribution of low-concentration multivalence ions in solid-state materials and offers a deeper understanding of the approaches to precisely resolve the subtle changes in the crystal structure.
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CuLaO2 is a rare-earth and dopant-free inorganic compound able to emit green light upon blue excitation. Its absorption amounts to 90% but its internal quantum efficiency is poor (<17%). The origin of this deleterious radiationless behavior is addressed by investigating the spectroscopic properties of this compound under the action of temperature and hydrostatic pressure in the 15-400 K and 1 bar-40 kbar intervals, and by combining the spectroscopic data with earlier results of DFT calculations. A two-step radiationless process is demonstrated, involving radiative re-absorption and cross-over to excitonic states.
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Endowing a single material with various types of luminescence, that is, exhibiting a simultaneous optical response to different stimuli, is vital in various fields. A photoluminescence (PL)- and mechanoluminescence (ML)-based multifunctional sensing platform is built by combining heterojunctioned ZnS/CaZnOS:Mn2+ mechano-photonic materials using a 3D-printing technique and fiber spinning. ML-active particles are embedded in micrometer-sized cellulose fibers for flexible optical devices capable of emitting light driven by mechanical force. Individually modified 3D-printed hard units that exhibit intense ML in response to mechanical deformation, such as impact and friction, are also fabricated. Importantly, they also allow low-pressure sensing up to ≈100 bar, a range previously inaccessible by any other optical sensing technique. Moreover, the developed optical manometer based on the PL of the materials demonstrates a superior high-pressure sensitivity of ≈6.20 nm GPa-1 . Using this sensing platform, four modes of temperature detection can be achieved: excitation-band spectral shifts, emission-band spectral shifts, bandwidth broadening, and lifetime shortening. This work supports the possibility of mass production of ML-active mechanical and optoelectronic parts integrated with scientific and industrial tools and apparatus.
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This research focuses on LPE growth, and the examination of the optical and photovoltaic properties of single crystalline film (SCF) phosphors based on Ce3+-doped Y3MgxSiyAl5-x-yO12 garnets with Mg and Si contents in x = 0-0.345 and y = 0-0.31 ranges. The absorbance, luminescence, scintillation, and photocurrent properties of Y3MgxSiyAl5-x-yO12:Ce SCFs were examined in comparison with Y3Al5O12:Ce (YAG:Ce) counterpart. Especially prepared YAG:Ce SCFs with a low (x, y < 0.1) concentration of Mg2+ and Mg2+-Si4+ codopants also showed a photocurrent that increased with rising Mg2+ and Si4+ concentrations. Mg2+ excess was systematically present in as-grown Y3MgxSiyAl5-x-yO12:Ce SCFs. The as-grown SCFs of these garnets under the excitation of α-particles had a low light yield (LY) and a fast scintillation response with a decay time in the ns range due to producing the Ce4+ ions as compensators for the Mg2+ excess. The Ce4+ dopant recharged to the Ce3+ state after SCF annealing at T > 1000 °C in a reducing atmosphere (95%N2 + 5%H2). Annealed SCF samples exhibited an LY of around 42% and similar scintillation decay kinetics to those of the YAG:Ce SCF counterpart. The photoluminescence studies of Y3MgxSiyAl5-x-yO12:Ce SCFs provide evidence for Ce3+ multicenter formation and the presence of an energy transfer between various Ce3+ multicenters. The Ce3+ multicenters possessed variable crystal field strengths in the nonequivalent dodecahedral sites of the garnet host due to the substitution of the octahedral positions by Mg2+ and the tetrahedral positions by Si4+. In comparison with YAG:Ce SCF, the Ce3+ luminescence spectra of Y3MgxSiyAl5-x-yO12:Ce SCFs greatly expanded in the red region. Using these beneficial trends of changes in the optical and photocurrent properties of Y3MgxSiyAl5-x-yO12:Ce garnets as a result of Mg2+ and Si4+ alloying, a new generation of SCF converters for white LEDs, photovoltaics, and scintillators could be developed.
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Erbium (Er) complexes are used as optical gain materials for signal generation in the telecom C-band at 1540 nm, but they need a sensitizer to enhance absorption. Na+ substitution for Ag+ and Bi3+ doping at the In3+ site is a possible strategy to enhance the broadband emission of Cs2AgInCl6, which could be used as a sensitizer for energy transfer to rare-earth elements. Herein, self-trapped exciton (STE) energy transfer to Er3+ at 1540 nm in double perovskite is reported. An acid precipitation method was used to synthesize Cs2AgInCl6 and its derivatives with Er3+, Bi3+, and Na+. Bare Cs2AgInCl6:Er emission signals were found to be weak at 1540 nm, but Bi3+ doping increased them by 12 times, and Bi3+ and Na+ doping increased signal intensity by up to 25 times. Electron paramagnetic resonance spectroscopy characterized a decrease in axial symmetry over the Er3+ ions after the substitutions of Na+ and Bi3+ in Cs2AgInCl6 at low temperatures (<7 K) for the first time. Moreover, an increase in pressure compressed the structure, which tuned the STE transition for free exciton emission, and a further increase in pressure distorted the cubic phase above 70 kbar.
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This study presents the impact of temperature and pressure on AlN:Mn2+ luminescence kinetics. Unusual behavior of Mn2+ optical properties during UV excitation is observed, where a strong afterglow luminescence of Mn2+ occurs even at low temperatures. When the temperature increases, the contribution of the afterglow luminescence is further enhanced, causing a significant increase in the luminescence intensity. The observed phenomena may be explained by an energy diagram in which the ON-VAl complex in AlN:Mn2+ plays a key role. Hence the ON-VAl complex defect in AlN:Mn2+ plays a double role. When the ON-VAl defect is located close to Mn2+ ions, it is responsible for transferring excitation energy directly to Mn2+ ions. However, when the ON-VAl defect complex is located far from Mn2+ ions, its excited state level acts as an electron trap responsible for afterglow luminescence. Additionally, three models have been tested to explain the structure of the emission spectrum and the strong asymmetry between the excitation and emission spectra. From the most straightforward configuration coordinate diagram through the configuration coordinate diagram model assuming different elastic constants in the excited and ground-states ending by a model based on the Jahn-Teller effect. We proved that only the Jahn-Teller effect in the excited 4T1 electronic state with spin-orbit coupling could fully explain the observed phenomena. Finally, high-pressure spectroscopic results complemented by the calculations of Racah parameters and the Tanabe-Sugano diagram are presented.
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Here, we report a halide precursor acid precipitation method to synthesize Cs2AgIn1-xBixCl6 (x = 0, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64, and 1) microcrystals. Cs2AgInCl6 and Bi derivative double perovskites show broadband white light emission via self-trapped excitons (STEs) and have achieved the highest internal quantum efficiency of up to 52.4% at x = 0.08. Synchrotron X-ray diffraction confirmed the linear increase of lattice parameters and cell volume with Bi3+ substitution at In3+ sites. Absorbance, photocurrent excitation, and photoluminescence excitation spectra are used to observe possible transitions from the valence to the conduction band or free exciton (FE) states as well as transitions within local Bi3+ states. The broadband photoluminescence is quenched via a single nonradiative process with an activation energy ΔE = 1490 cm-1 for Cs2AgIn0.92Bi0.08Cl6. Under normal conditions, we observed STE emission, but applying external pressure alters the electronic structure such that at elevated pressure, the only emission via the FE state is observed. We anticipate that structure, temperature and pressure-dependent photoluminescence studies will help the future use of a single-source lead-free double perovskite for white light-emitting diode applications.
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Organic-inorganic hybrid metal halides have recently attracted attention in the global research field for their bright light emission, tunable photoluminescence wavelength, and convenient synthesis method. This study reports the detailed properties of (C10H16N)2MnBr4, which emits bright green light with a high photoluminescence quantum yield. Results of powder X-ray diffraction, photoluminescence, thermogravimetric analysis, and Raman spectra show the phase transition of (C10H16N)2MnBr4 at 430 K. This phase transition was identified as the solid to liquid state of (C10H16N)2MnBr4. Moreover, the pressure- and temperature-induced relationship between structural and optical properties in (C10H16N)2MnBr4 can be identified. This investigation provides deep insights into the luminescent properties of metal halide crystals and promotes further research.
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Portable near-infrared (NIR) light sources are in high demand for applications in spectroscopy, night vision, bioimaging, and many others. Typical phosphor designs feature isolated Cr3+ ion centers, and it is challenging to design broadband NIR phosphors based on Cr3+-Cr3+ pairs. Here, we explore the solid-solution series SrAl11.88-xGaxO19:0.12Cr3+ (x = 0, 2, 4, 6, 8, 10, and 12) as phosphors featuring Cr3+-Cr3+ pairs and evaluate structure-property relations within the series. We establish the incorporation of Ga within the magentoplumbite-type structure at five distinct crystallographic sites and evaluate the effect of this incorporation on the Cr3+-Cr3+ ion pair proximity. Electron paramagnetic measurements reveal the presence of both isolated Cr3+ and Cr3+-Cr3+ pairs, resulting in NIR luminescence at approximately 650-1050 nm. Unexpectedly, the origin of broadband NIR luminescence with a peak within the range 740-820 nm is related to the Cr3+-Cr3+ ion pair. We demonstrate the application of the SrAl5.88Ga6O19:0.12Cr3+ phosphor, which possesses an internal quantum efficiency of â¼85%, a radiant flux of â¼95 mW, and zero thermal quenching up to 500 K. This work provides a further understanding of spectral shifts in phosphor solid solutions and in particular the application of the magentoplumbites as promising next-generation NIR phosphor host systems.
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Cs4PbI6, as a rarely investigated member of the Cs4PbX6 (X is a halogen element) family, has been successfully synthesized at low temperatures, and the synthetic conditions have been optimized. Metal iodides such as LiI, KI, NiI2, CoI2, and ZnI2, as additives, play an important role in enhancing the formation of the Cs4PbI6 microcrystals. ZnI2 with the lowest dissociation energy is the most efficient additive to supply iodide ions, and its amount of addition has also been optimized. Strong red to near-infrared (NIR) emission properties have been detected, and its optical emission centers have been identified to be numerous embedded perovskite-type α-CsPbI3 nanocrystallites (â¼5 nm in diameter) based on investigations of temperature- and pressure-dependent photoluminescent properties. High-resolution transmission electron microscopy was used to detect these hidden nanoparticles, although the material was highly beam-sensitive and confirmed a "raisin bread"-like structure of the Cs4PbI6 crystals. A NIR mini-LED for the biological application has been successfully fabricated using as-synthesized Cs4PbI6 crystals. This work provides information for the future development of infrared fluorescent nanoscale perovskite materials.
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Near-infrared (NIR) phosphors are fascinating materials that have numerous applications in diverse fields. In this study, a series of La3Ga5GeO14:Cr3+ phosphors, which was incorporated with Sn4+, Ba2+, and Sc3+, was successfully synthesized using solid-state reaction to explore every cationic site comprehensively. The crystal structures were well resolved by combining synchrotron X-ray diffraction and neutron powder diffraction through joint Rietveld refinements. The trapping of free electrons induced by charge unbalances and lattice vacancies changes the magnetic properties, which was well explained by a Dyson curve in electron paramagnetic resonance. Temperature and pressure-dependent photoluminescence spectra reveal various luminescent properties between strong and weak fields in different dopant centers. The phosphor-converted NIR light-emitting diode (pc-NIR LED) package demonstrates a superior broadband emission that covers the near-infrared (NIR) region of 650-1050 nm. This study can provide researchers with new insight into the control mechanism of multiple-cation-site phosphors and reveal a potential phosphor candidate for practical NIR LED application.
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Cs4PbBr6 is regarded as an outstanding luminescent material with good thermal stability and optical performance. However, the mechanism of green emission from Cs4PbBr6 has been controversial. Here we show that isolated CsPbBr3 nanoparticles embedded within a Cs4PbBr6 matrix give rise to a "normal" green luminescence while superfluorescence at longer wavelengths is suppressed. High-resolution transmission electron microscopy shows that the embedded CsPbBr3 nanoparticles are around 3.8 nm in diameter and are well-separated from each other, perhaps by a strain-driven mechanism. This mechanism may enable other efficient luminescent composites to be developed by embedding optically active nanoparticles epitaxially within inert host lattices.
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Phosphors with a rigid and symmetrical structure are urgently needed. The alkali lithosilicate family (A[Li3SiO4]) has been extensively studied with a narrow emission band due to its unique cuboid-coordinated environment and rigid structure. However, here we demonstrate for the first time Ce-doped NaK2Li[Li3SiO4]4 phosphors with a broad emission band, a high internal quantum efficiency (85.6%), and excellent thermal stability. Photoluminescence indicates the Ce's preference to occupy the Na+ site, leading to a strong blue color emission with peak maxima at 417 and 450 nm. Temperature- and pressure-dependent photoluminescence reveals thermal stability and a phase transition. Moreover, the X-ray absorption near-edge structure reveals the mixing of Ce3+ and Ce4+ in the materials; this result differs from that of Eu2+-doped A[Li3SiO4] phosphors. The charge compensation process is then proposed to explain this difference. This study not only provides insights into Ce-doped UCr4C4-type phosphors but also explains the charge compensation mechanism of the aliovalent doping process.
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The process of persistent luminescence or glow-in-the-dark, the delayed emission of light of irradiated substances, has long fascinated researchers, who have made efforts to explain the underlying physical phenomenon as well as put it to practical use. However, persistent luminescence is an elusive and difficult process, both in terms of controlling or altering its properties, as well as providing a quantitative description. In this paper, we used SrSi2N2O2:Eu2+ as a model persistent phosphor, characterized by the broad distribution of structural defects and exhibiting long-lasting Eu2+ luminescence that is visible for a few minutes after switching off UV light. We investigated the persistent luminescence process by two complementary methods, namely, thermoluminescence and temperature-dependent persistent luminescence decay measurements. Analysis of experimental data allowed us to determine the depth distribution of traps, and allowed us to distinguish two different mechanisms by which the emission is delayed. The first, the temperature-dependent mechanism, is related to trap activation, while the second, temperature-independent mechanism is related to carrier migration. Finally, we employed the strategy of the co-doping of the phosphor SrSi2N2O2:Eu2+,M3+ (M = Ce, Nd, Dy) to modify the persistent luminescence properties.
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The systematic substitution of Ba in the Sr site of Sr[Mg2Al2N4]:Eu2+ generates a deep-red-emitting phosphor with enhanced thermal luminescence properties. Gas pressure sintering (GPS) of all-nitride starting materials in Molybdenum (Mo) crucibles yields pure-phase red-orange-colored phosphors. Peaks in the synchrotron X-ray diffraction (SXRD) data show a systematic shift toward smaller angles due to the introduction of the larger Ba cation in the same crystal structure. The photoluminescence property reveals that Ba substitution shifts the original emission wavelength of Sr[Mg2Al2N4]:Eu2+ (625 nm) toward â¼690 nm for Ba[Mg2Al2N4]:Eu2+. Thermal stability measurement of Sr1-xBax[Mg2Al2N4] indicates a systematic increase in stability from x = 0 to x = 1. X-ray absorption near-edge spectroscopy (XANES) results demonstrate the coexistence of Eu2+ and Eu3+. The red-shift and the enhanced thermal stability reveals that the distance of the emitting 5d level to the conduction band of Ba[Mg2Al2N4]:Eu2+ is large. The ionic size mismatch of Eu occupying a Ba site reduces the symmetry, thereby further splitting the degenerate emitting 5d level and lowering the energy of the emitting center. The development of deep-red phosphors emitting at 670-690 nm (x = 0.8-1.0) offers possible candidates for plant lighting applications.
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Two types of infrared fluoride phosphors, Cr3+-doped K3AlF6 and K3GaF6, were developed in this research. The K3Al1-xF6:xCr3+ and K3Ga1-yF6:yCr3+ fluoride phosphors were proven to be pure phase via X-ray diffraction refinement, which demonstrated that the procedure can be applied to large-scale production. Electron paramagnetic resonance measurements indicated that Cr3+ ions in cubic with respect to noncubic are coupled better with K3GaF6 than with K3AlF6. The main differences between these two phosphors, the site symmetry and pressure behavior of the spectra, were obtained in temperature- and pressure-dependent spectra. According to the calculation results, Cr3+ in fluorine coordination at ambient pressure indicates an intermediate crystal field. For the phosphor-converted light-emitting diodes (LEDs) fabricated from these two phosphors, the spectral range is from 650 to 1000 nm, which resulted in a radiant flux of 7-8 mW with an input power of 1.05 W. The research reveals detailed luminous properties, which will lead to a new way of studying Cr3+-doped fluoride phosphors and their application in LEDs.