Luminescence Variations Research Articles

Influence of flame stability on iron oxide nanoparticle growth during FSP

Flame stability during flame spray pyrolysis (FSP) remains an active topic of investigation due to its impact on synthesised particle attributes and purity. The unique feature of the burner investigated here is the ability to control flame stability over newly defined stability maps. The novelty of the current work lies in understanding the influence of these broad stability modes on nanoparticle growth during FSP and on the attributes of collected products. Several distinct flame configurations are selected for iron oxide nanoparticle synthesis, ranging from stable to highly unstable flames. The flame stability regimes are characterised by OH∗ chemiluminescence and broadband flame luminescence imaging. Stability is correlated with the coefficient of variation of flame luminescence (CV) and flame height with mean OH∗ chemiluminescence. Planar Mie scattering is then used to identify the effect of flame luminescence intermittency on spray atomisation and evaporation quality. For particle analysis, in-situ thermophoretic sampling is performed from 30 to 200 mm above the burner exit plane and analysed via transmission electron microscopy (TEM). Further ex-situ analysis is also performed on the bulk-collected product via high-resolution TEM, X-ray powder diffraction (XRD), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). It is demonstrated that flames with higher instability (CVmin ≥ 0.35) maintain increased spray heights (>26 %) and reduced flame heights (>79 %) compared to stable flames with the same precursor volume flowrate. This reduces the high-temperature particle residence time for primary particle growth and impacts subsequent agglomeration. For example, the mean diameter of gyration and primary particle diameter are found to vary by 44 % and 29 % depending on the flame regime, respectively. Ex-situ analysis also demonstrates that the dominant iron oxide phase produced is maghemite regardless of the stability regime. However, higher concentrations of organic impurities including methyl, methylene and carboxylate functional groups are found via ATR-FTIR with increased flame instability (CV).

Synthesis and luminescent properties of five-six-membered bis(metallacyclic) platinum(II) complexes bearing polypyridine alkynes

A series of five-six-membered bis(metallacyclic) Pt(II) complexes bearing a 2,2′-bipyridine (BPY) or 2,2′:6′,2"-terpyridine (TPY) ethynyl ligand were synthesized and characterized. The structures of N^C*N-coordinated Pt(II) complexes (−)-1 and (−)-5 were confirmed by single crystal X-ray diffraction, displaying a slightly distorted square-planar coordination environment around the Pt(II) centers. Compared to N^N*C-coordinated Pt(II) derivatives ((−)-2, (−)-4 and (−)-6), N^C*N-coordinated complexes ((−)-1, (−)-3 and (−)-5) demonstrate a more significant AIE property with a sharp luminescence variation in response to water content. In addition, due to the existence of the pendent BPY or TPY unit, N^C*N-coordinated Pt(II) complexes show a luminescence response to Zn2+ ions. Cytotoxicity and cell imaging of luminescent five-six-membered bis(metallacyclic) Pt(II) complexes with polypyridine alkynes have been evaluated.

Octahedron vacancy induced luminescence improvement of double perovskite type phosphors LaMg2/3-xNb1/3O3:Mn4+ with multifunctional applications

Near infrared (NIR) phosphors have been booming as promising candidates for agriculture due to the adjustable spectrum and excellent match with the dyes of the plants. Here, Mn4+ activated double perovskite LaMg2/3Mn1/3O3 NIR phosphor was prepared, which showed high match with the absorption spectra of phytochrome PFR. Concentration of Mg2+ was decreased to create octahedron vacancy into the lattice to improve the luminescence performance. Structure and luminescence variation of the phosphors LaMg2/3-xNb1/3O3:Mn4+ along with the increased vacancy concentration were carried out. Relative sensitivity Sr of the optimized LaMg0.57Nb0.33O3:Mn4+ reaches 3.109 % and exhibits great application potential in temperature sensor. Both the NIR light emitting diode (LED) and white LED were fabricated by using this double perovskite NIR phosphor and applied to the cultivation of dragon fruit as light compensation. The dragon fruits matured faster than those without any light compensation. These results confirm the great application potential of this double perovskite NIR phosphor in temperature sensor and plant cultivation.

Piezofluorochromism in Hierarchical Porous π‐stacked Supermolecular Spring Frameworks from Aromatic Chiral Cages

AbstractPiezochromic materials that exhibit pressure‐dependent luminescence variations are attracting interest with wide potential applications in mechanical sensors, anticounterfeiting and storage devices. Crystalline porous materials (CPMs) have been widely studied in piezochromism for highly tunable luminescence. Nevertheless, reversible and high‐contrast emission response with a wide pressure range is still challenging. Herein, the first example of hierarchical porous cage‐based πOF (Cage‐πOF‐1) with spring structure was synthesized by using aromatic chiral cages as building blocks. Its elastic properties evaluated based on the bulk modulus (9.5 GPa) is softer than most reported CPMs and the collapse point (20.0 GPa) significantly exceeds ever reported CPMs. As smart materials, Cage‐πOF‐1 displays linear pressure‐dependent emission and achieves a high‐contrast emission difference up to 154 nm. Pressure‐responsive limit is up to 16 GPa, outperforming the CPMs reported so far. Dedicated experiments and density functional theory (DFT) calculations illustrate that π–π interactions‐dominated controllable structural shrinkage and porous‐spring‐structure‐mediated elasticity is responsible for the outstanding piezofluorochromism.

Piezofluorochromism in Hierarchical Porous π-stacked Supermolecular Spring Frameworks from Aromatic Chiral Cages.

Piezochromic materials that exhibit pressure-dependent luminescence variations are attracting interest with wide potential applications in mechanical sensors, anticounterfeiting and storage devices. Crystalline porous materials (CPMs) have been widely studied in piezochromism for highly tunable luminescence. Nevertheless, reversible and high-contrast emission response with a wide pressure range is still challenging. Herein, the first example of hierarchical porous cage-based πOF (Cage-πOF-1) with spring structure was synthesized by using aromatic chiral cages as building blocks. Its elastic properties evaluated based on the bulk modulus (9.5 GPa) is softer than most reported CPMs and the collapse point (20.0 GPa) significantly exceeds ever reported CPMs. As smart materials, Cage-πOF-1 displays linear pressure-dependent emission and achieves a high-contrast emission difference up to 154 nm. Pressure-responsive limit is up to 16 GPa, outperforming the CPMs reported so far. Dedicated experiments and density functional theory (DFT) calculations illustrate that π-π interactions-dominated controllable structural shrinkage and porous-spring-structure-mediated elasticity is responsible for the outstanding piezofluorochromism.

Highly efficient persistent luminescent nanozymes-based luminescence-colorimetric dual-mode sensor for total antioxidant capacity assay

Total antioxidant capacity (TAC) is a vital parameter to assess the gross antioxidant activity in biological and food matrices. Accurate determination of TAC has become increasingly important for health monitoring and dietary guidance. Here, we report a persistent luminescent nanozyme (ZGO-Pt) based luminescence-colorimetric dual-mode sensor for selective determination of TAC. ZGO-Pt was fabricated based on ZnGa2O4:Cr nanoparticles (ZGO) with platinum nanoflower as synthetic additive. The prepared ZGO-Pt exhibited fascinating peroxidase-mimetic activity and persistent luminescence, and enabled effectively catalysis of the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxTMB. Meanwhile, the generated oxTMB gave strong absorption at 652 nm to quench the luminescence of ZGO-Pt at 700 nm via the inner filter effect. Antioxidants could compete with the oxidable TMB or reduce oxTMB to TMB, resulting in the simultaneous variations of blue color and luminescence to provide the basis for dual-mode assay for TAC. The highly efficient catalysis of ZGO-Pt (Km, 3.12 mM for H2O2, 0.592 mM for TMB) allows the dual-mode sensor to realize precise determination of TAC with a wide linear range (0.5–200 μM and 1–300 μM for colorimetric and luminescence mode, respectively) and low limit of detection (LOD, 0.05 μM and 0.78 μM for colorimetric and luminescence mode, respectively). The developed dual-mode sensor was successfully applied to the determination of TAC in vitamin tablet, beverages and fruits. This work provides an efficient persistent luminescent nanoparticle-based nanozyme for a facile TAC assay with further vision in biosensing and food technology.

Influence of Annealing Temperature on the Structural and Luminescence Features and Thermoluminescence Trap Parameters of Ca2Al2SiO7: Ce3+ Phosphors

Cerium-doped Ca2Al2SiO7 phosphors were synthesized via the combustion technique and annealed at 1073 K, 1173 K, and 1373 K. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), photoluminescence (PL), and thermoluminescence (TL) studies were performed to explore the variation of structural, morphological, luminescence, and TL properties with annealing temperature. The XRD plot showed an increase in crystallinity with an increase in annealing temperature. Similarly, the enhancement of PL intensity with an increase in annealing temperature supports the increased crystallinity of the phosphor samples. Detailed analysis of traps and trap parameters was carried out using the principle of TL. Samples were irradiated with different γ-ray doses, and, on heating, luminescence was observed. Thus, TL glow curves were drawn and deconvoluted using computerized glow curve deconvolution (CGCD) and Chen’s peak shape method to study the traps and trap parameters. With increasing annealing temperature, an increase in TL intensity was observed. Regardless of annealing temperature, every sample displayed a linear dose–response for doses ranging from 3 Gy to 500 Gy. TL investigations suggested that the produced phosphors are suitable candidates for gamma dosimetry applications.

An instrument-free photoluminescent sensor array based on “turn-off” bimetallic lanthanide metal–organic frameworks for antibiotic determination

The widespread use of antibiotics results in harmful residues, posing a serious threat to ecosystems and human health. Given synergetic or antagonistic toxicological features often exist among different antibiotics, it is vital to develop methods to synchronously determine these contaminants. Herein, we develop a hand-held photoluminescent sensor array based on “turn-off” bimetallic lanthanide metal–organic frameworks (MOFs) to realize the identification and quantification of six common antibiotics. Three Tb/Eu-MOFs with different bimetallic proportions were synthesized and employed to provide signals toward multiple antibiotics based on their differential contributions to the photoluminescence quenching of these probes. By designing a 3D-printed smartphone-equipped signal capturing platform, tiny luminescence variations induced by different antibiotics were recorded and processed for the classification and identification of these targets via pattern recognition analysis. Compared to conventional sensor arrays requiring cumbersome signal reading instruments and complex sensing units, our platform really enables instrument-free in-field detection of multiple targets with only a basic material. The platform could identify not only single antibiotics in a wide level scope but also various combinations of two, three or even four antibiotics with good discrimination capacity. Differentiation of multiple antibiotics in river water, milk, and urine matrices was also demonstrated. Furthermore, over 90% accuracy was gained for unknown samples in double-blind tests. Our work offers a portable, low-cost, and high-performance tool to determine multiple antibiotics simultaneously, which will stimulate future exploration of hand-held sensor arrays with simple sensing elements for on-site analysis and point-of-care diagnosis.

Facile preparation of carbon dots with multicolor emission for fluorescence detection of ascorbic acid, glutathione and moisture content

The nitrogen-doped carbon dots (N-CDs) with multicolor emission (green, yellow, and red) were fabricated with naphthalenetetracarboxylic dianhydride as carbon precursor, and different alkylamines as passive agents. The structures of the as-prepared carbon dots were confirmed by the Fourier transform infrared (FT-IR) spectrum, X-ray photoelectron spectroscopy (XPS) spectra, transmission electron microscopy (TEM), Raman spectra, and X-ray diffraction (XRD) pattern. The characterized results and UV–vis absorption spectrum demonstrated that the luminescence variations of different CDs were probably attributed to the difference of N-related states, oxygen-containing groups, and oxidation degree in the CDs structure. Moreover, the green emitting CDs (G-CDs) could be utilized as fluorescent probe for ascorbic acid (AA) detection with detection limit (LOD) of 5 μM. The yellow emitting CDs (Y-CDs) could be used to detect glutathione (GSH) in the range of 1–70 μM with LOD of 0.07 μM. The red emitting CDs (R-CDs) could detect the water content in THF, DMF, acetone, and EtOH with LODs of 0.44%, 0.31%, 0.55% and 0.55%, respectively. Remarkably, G-CDs and Y-CDs can distinguish AA and GSH respectively with high selectivity and accuracy. Finally, the fluorescent probes based on G-CDs and Y-CDs were successfully applied for the AA and GSH determination in vitamin C tablet, grapefruit juice, and GSH whitening serum samples with high reliability and feasibility, which provided the guidance for the selection of AA and GSH supplements.

Imaging local luminescence variations in CdSe0.1Te0.9 thin films grown by the colossal grain growth process

Imaging local luminescence variations in CdSe0.1Te0.9 thin films grown by the colossal grain growth process

Helicity-modulated remote C-H functionalization.

Remote C-H functionalization is highly important for the conversion and utilization of arenes, but the conventional routes are comprehensively developed with the assistance of transition metal catalysts or templates. We report a facile metal/template-free electrochemical strategy for remote C-H functionalization in a helical system, where aromatic or aliphatic hydrogen act as a directing group to promote the alkoxylation at the opposite site of the helical skeleton by generating a unique helical "back-biting" environment. Such helicity-modulated C-H functionalization is prevalent for carbo[n]helicenes (n=6 to 9, primitive or substituted) and hetero[6]helicenes and also occurs when the aryl hydrogen on the first position is replaced by a methyl group or a phenyl group. Thus, the relatively inert helicene skeleton can be precisely furnished with a rich array of alkoxy pendants with tunable functional moieties. Notably, the selective decoration of a methoxy group on N-methylated aza[6]helicene close or distant to the nitrogen atom leads to distinct luminescence variation upon changing the solvents.

Tough, Self-Healing, and UV Light-Switchable Luminescent Hydrogels with Reversible Stimuli-Responsive Properties for Cu2+

Stimuli-responsive luminescent hydrogels (LHs) are of great potential for applications in advanced luminescent sensors; however, structural optimizations and challenges in implementation still remain in their practical applications. Herein, we reported a promising and cooperative strategy to prepare smart LH actuators. Lanthanide(III)-based complexes (LnCs) and sulfur quantum dots (S-QDs) in this contribution are constructed in a cooperative manner; that is, (1) a noncovalent hydrogen bonding model between polyethylene glycol (PEG) in S-QDs and polyurethane (PU) endows LHs with interwoven double networks and improved the mechanical properties and (2) LnCs and S-QDs are two excellent emitting centers with different luminescent excitation properties, leading to the modulating emission colors of LHs by varying the UV irradiation between 254 and 365 nm. Meanwhile, the resultant LHs containing 3.26 wt % of PU possess good mechanical performance and self-healing capability. As a proof of application in stimuli response, our LHs can be served as a ratiometric luminescence probe to electively detect Cu2+ via exponentially correlating the emission intensity ratio of LnCs and S-QDs to the Cu2+ concentration. Remarkably, the obtained LHs also show reversible luminescence “On/Off” switch upon alternate exposure to Cu2+/glutathione (GSH) under 254 nm, while no obvious luminescent variation is observed under 365 nm.

Tuning defect-related optical bands by channeling implants in semiconductors

Ion implantation is an excellent method to introduce defects into semiconductors, extending their functionalities in a controllable way. Herein, we investigated an option to use crystallographically aligned implants as an additional route to control the balance between optically active defects, selecting ZnO as a test material. The optical data were correlated with the structural analysis confirming the formation of different dominating crystalline defects in samples implanted along and off [0001] direction. Specifically, we demonstrated that different proportions in the contents of the extended and point defects in the initial as-implanted states of these samples, lead to prominent variations in the defect-related luminescence upon annealing. As such, we conclude that channeling implants may have an added value in the functionalization of defects in semiconductors, e.g. to tune specific spectral contents in the defect-related emission bands.

Tunable and Thermally Stable Luminescence from Polycyclic Aromatic Hydrocarbons Confined in a Zeolitic Imidazolate Framework

AbstractMetal–organic frameworks (MOFs) can provide a variety of nanocompartments for the confinement of guest molecules. Furthermore, the emissions of fluorescent molecules can be tuned by confinement. In this study, a solvent‐free “bottle‐around‐ship” method is used to encapsulate perylene and 9,10‐dimethylanthracene, two polycyclic aromatic hydrocarbons, in the MOF ZIF‐8. Luminescence color tuning is achieved, including white‐light emission, when controlling the loading of only a single type of guest. Photophysical analysis suggests that the variations in luminescence result from various guest arrangements in the nanocompartments, as well as host–guest interactions. Because of the tight confinement of the guests, this host–guest system displays excellent luminescence thermal stability.

Influence of NaYF4 Inert and Active Layer on Upconversion Luminescence.

NaYF4:Yb,Er@NaYF4 core–shell nanostructures were prepared to investigate their influence on upconversion (UC) luminescence. Tests revealed green radiation (4S3/2→4I15/2) and red radiation (4F9/2→4I15/2) first increased and then gradually decreased as Yb concentration increased in the NaYF4 shell. The strongest fluorescent radiation occurred at an Yb concentration of 5%. To investigate the complicated variation of luminescence, we designed a set of experiments to study the impact of Yb ion concentration on luminescence intensity, and we analyzed the corresponding enhancement mechanism. It is probable that the energy transfers between both Yb and Er ions and Yb and Yb ions are involved in the UC processes. The enhancement of hybrid nanostructures has huge potential in biological detection and solar cells.

Effect of Diode Field on Time-Resolved Photoluminescence of CdTe-Based Solar Cells

Time-resolved photoluminescence (TRPL) measurements with externally applied voltage bias were performed on a variety of thin-film CdTe-based solar cells. These measurements revealed a substantial variation in luminescence decays with the application of external voltage bias in many of the samples. Experimental results were replicated with a MATLAB-based modeling tool. Decay variations are attributed to the changing strength of internal p-n junction electric fields as bias is modulated; this exercise, therefore, illustrates whether or not field effects influence a particular TRPL measurement and how. It is found via modeling that the field influence on TRPL decays is dependent on the cell's bulk minority carrier lifetime, mobility, and carrier concentration, as well as the laser excitation power during a measurement. While nearly insignificant in poorer quality legacy cells, the field effects are substantial in state-of-the-art CdTe cells with high lifetime, mobility, and doping, complicating determination of bulk lifetime. It is found that forward bias is effective in eliminating junction fields. It is also shown that fields can be effectively suppressed by increasing excitation power, but doing so is imprecise and can also introduce additional errors unrelated to fields. It is therefore concluded that lifetime is most accurately measured in completed cells under forward bias at low excitation intensity.

Rapid in situ assessment of luminescence-bleaching depths for deriving burial and exposure chronologies of rock surfaces

Recent developments in luminescence dating offer new ways to date exposure and burial durations of rocks. The new rock surface dating methods ideally require high-resolution data, faster sample preparation and measurement times, and field screening methods to select samples with appropriate luminescence characteristics and bleaching histories. Presented here is a demonstration of an EMCCD (electron multiplying charge coupled device) based system capable of imaging high-resolution infrared stimulated luminescence (IRSL) and infrared-photoluminescence (IRPL) from rock samples. The IRPL can be detected at both 880 nm and 955 nm. Using this instrument, the entire luminescence-depth profile can be reconstructed by imaging a single surface cut perpendicular to the exposed rock face. We demonstrate the possibility of reconstructing luminescence-depth profiles suitable for rock surface dating from large (cm-scale) rock samples, without using a regeneration dose for normalisation of the natural luminescence signals. Based on the different bleaching characteristics of the IRSL and IRPL emissions at 880 nm and 955 nm, we show that it is possible to gain reliable estimates of bleaching depths from measurement of as few as two images of the IRPL signal (one for each emission), or from measurement of the IRSL decay curve. We thus by-pass laborious sample preparations and the need for a gamma source to estimate the bleaching depth, thereby extending the 2D luminescence-depth profile imaging technique to other laboratories that lack access to ionising radiation facilities. This study also makes a significant progression towards development of a field instrument for in situ relative exposure dating, and sample screening for rock surface burial dating. • Direct imaging of luminescence-depth profiles in rocks using IRPL or IRSL. • New methods for normalising spatial variations in luminescence without irradiation. • Characterising bleachability of different OSL emissions from the principal trap. • Rock surface dating for rapid field analysis or laboratories lacking irradiation facilities.

Amino group-driven distinguishing homocysteine from cysteine and glutathione in photoluminesecent signal of the iridium(III) complexes

In this work, six iridium(III) complexes have been designed, synthesized and characterized. The molecular structures of complex 1 ([(pba)2Ir(bpy-2N(CH3)2)]PF6), 2 ([(pba)2Ir(bpy-2NH2)]PF6) and 3 ([(pba)2Ir(bpy-2CH3)]PF6) were determined by single crystal X-ray diffraction. Upon addition of Hcy (homocysteine) to the solution of complex 1, a luminescent variation from orange red to green was observed by the naked eye, corresponding to a large blue shift from 604 nm to 498 nm (~106 nm). While the emission intensity of complex 1 was almost no change after addition of other common amino acids including Cys (cysteine) and GSH (glutathione). The aldehyde group of complex 1 formed a new thiazinane/thiazolidine ring with Hcy/Cys confirmed by 1H NMR and high-resolution mass spectrometry. And the new product 1-Hcy had a higher quantum yield than 1-Cys. Theoretical calculations showed that the HOMO (highest occupied molecular orbital) of 1-Hcy was located on the newly formed six-membered thiazinane ring, which was different from the HOMO of 1-Cys. Compared with the other iridium(III) complexes, we can speculate that the large blue shift and enhancement of the emission intensity of the complex 1 were related to the strong electron donating ability of the modified amino groups on bipyridine ligand. This will provide an idea for the design of ratio-based luminescence probes for Hcy in future.

Dual-Emissive Persistent Luminescence Nanoparticle-Based Charge-Reversible Intelligent Nanoprobe for Persistent Luminescence-Ratio Bioimaging along with Chemo-Photothermal Synergic Therapy

Persistent luminescence nanoparticles (PLNPs) hold great promise for bioimaging owing to no demand for in situ excitation and negligible tissue autofluorescence interference. Nevertheless, huge challenges remain in the further development of single-emissive PLNPs due to the great variation of luminescence with time after excitation ceases. Herein, we report the controllable fabrication of dual-emissive monodispersed PLNPs (ZnGa2O4:Cr) by a surfactant-assisted hydrothermal method in combination with postcalcination for bioimaging. The prepared PLNPs emit luminescence at 508 and 714 nm with a constant luminescence ratio (I508/I714) for more than 1 h after UV excitation stops. Moreover, the prepared PLNPs give a constant I508/I714 ratio signal after repeated excitation by a LED lamp, allowing luminescence ratio imaging to ensure the long-term accuracy for in vivo imaging. In vivo ratio imaging demonstrates the potential of the prepared PLNPs for precision bioimaging. In addition, the prepared PLNPs have been applied to fabricate a theranostic nanoprobe with intelligent tumor-targeted imaging and chemo-photothermal synergistic therapy to further reveal their unique advantage for imaging guided therapy. We believe that the dual-emissive PLNPs will provide a promising nanoplatform for bioimaging and biomedical applications.

Structure and up-conversion luminescence of Yb[formula omitted]/Ho[formula omitted] co-doped fluoroborate glasses

Yb3+/Ho3+ dual-doped fluoroborate glasses were obtained by high temperature melting process. Ultraviolet–visible spectrophotometer, XRD, FT-IR and fluorescence spectrometer were used to characterize the glass structure, transmittance, up-conversion (UC) emission spectrum and fluorescence decay time. The structural groups in all glasses were [BO4], [BO3] and [PO4] units. Transmissivity of all glass samples exceeds 60%. In addition, the fluorescence intensity ratio (FIR) technique was used to investigate the variation of UC luminescence at 543 nm (Ho3+: 5F4/5S2→5I8) and 659 nm (Ho3+: 5F5→5I8) under pump wavelength of 980 nm between 453 K and 653 K. The absolute sensitivity of glass sample at 653 K was 5 × 10−2 K−1 and the relative sensitivity was 9 × 10−4 K−1. The results indicated that Yb3+/Ho3+ co-doped fluoroborate glass has potential applications for up-conversion luminescence and optical temperature measurement.