Short Fluorescence Lifetime Research Articles

Improved fluorescent phytochromes for in situ imaging

Modern biology investigations on phytochromes as near-infrared fluorescent pigments pave the way for the development of new biosensors, as well as for optogenetics and in vivo imaging tools. Recently, near-infrared fluorescent proteins (NIR-FPs) engineered from biliverdin-binding bacteriophytochromes and cyanobacteriochromes, and from phycocyanobilin-binding cyanobacterial phytochromes have become promising probes for fluorescence microscopy and in vivo imaging. However, current NIR-FPs typically suffer from low fluorescence quantum yields and short fluorescence lifetimes. Here, we applied the rational approach of combining mutations known to enhance fluorescence in the cyanobacterial phytochrome Cph1 to derive a series of highly fluorescent variants with fluorescence quantum yield exceeding 15%. These variants were characterised by biochemical and spectroscopic methods, including time-resolved fluorescence spectroscopy. We show that these new NIR-FPs exhibit high fluorescence quantum yields and long fluorescence lifetimes, contributing to their bright fluorescence, and provide fluorescence lifetime imaging measurements in E.coli cells.

Multimodal bioimaging using nanodiamond and gold hybrid nanoparticles

Hybrid core–shell nanodiamond-gold nanoparticles were synthesized and characterized as a novel multifunctional material with tunable and tailored properties for multifunctional biomedical applications. The combination of nanostructured gold and nanodiamond properties afford new options for optical labeling, imaging, sensing, and drug delivery, as well as targeted treatment. ND@Au core–shell nanoparticles composed of nanodiamond (ND) core doped with Si vacancies (SiV) and Au shell were synthesized and characterized in terms of their biomedical applications. Several bioimaging modalities based on the combination of optical and spectroscopic properties of the hybrid nano-systems are demonstrated in cellular and developing zebrafish larvae models. The ND@Au nanoparticles exhibit isolated ND’s Raman signal of sp3 bonded carbon, one-photon fluorescence of SiV with strong zero-phonon line at 740 nm, two-photon excited fluorescence of nanogold with short fluorescence lifetime and strong absorption of X-ray irradiation render them possible imaging agent for Raman mapping, Fluorescence imaging, two-photon Fluorescence Lifetime Imaging (TP-FLIM) and high-resolution hard-X-ray microscopy in biosystems. Potential combination of the imaging facilities with other theranostic functionalities is discussed.

Stabilization of Lead-Reduced Metal Halide Perovskite Nanocrystals by High-Entropy Alloying.

Colloidal metal halide perovskite (MHP) nanocrystals (NCs) are an emerging class of fluorescent quantum dots (QDs) for next-generation optoelectronics. A great hurdle hindering practical applications, however, is their high lead content, where most attempts addressing the challenge in the literature compromised the material’s optical performance or colloidal stability. Here, we present a postsynthetic approach that stabilizes the lead-reduced MHP NCs through high-entropy alloying. Upon doping the NCs with multiple elements in considerably high concentrations, the resulting high-entropy perovskite (HEP) NCs remain to possess excellent colloidal stability and narrowband emission, with even higher photoluminescence (PL) quantum yields, ηPL, and shorter fluorescence lifetimes, τPL. The formation of multiple phases containing mixed interstitial and doping phases is suggested by X-ray crystallography. Importantly, the crystalline phases with higher degrees of lattice expansion and lattice contraction can be stabilized upon high-entropy alloying. We show that the lead content can be approximately reduced by up to 55% upon high-entropy alloying. The findings reported here make one big step closer to the commercialization of perovskite NCs.

Tryptophan capped gold-aryl nanoparticles for energy transfer study with SARS-CoV-2 spike proteins

ABSTRACT Current research on coronavirus 2 disease (SARS-CoV-2) has been focused on developing reliable gold nanomaterials and methods for the detection of viral spike protein (S-proteins). Here, we describe the fluorescence quenching of spike proteins in the presence of robust gold-aryl nanoparticles. The obtained results demonstrated a strong binding affinity between S-proteins and tryptophan immobilized on gold-carbon nanoparticles (Trp-AuNPs) based on the binding constant value of 11.098 M−1. Förster non-radiative energy transfer (FRET) calculations showed an average binding distance of r = 3.06 nm and a critical energy transfer distance of R0 = 2.5 nm. Time-resolved fluorescence studies of conjugated S-proteins onto Trp-AuNPs revealed a short fluorescence lifetime and dynamic quenching.

A red-emitting phosphor K5In3F14:Mn4+ and its potential application in the backlighting

A red-emitting phosphor with a short fluorescence lifetime plays an important role in LED backlighting. Herein, new red phosphor K5In3F14:Mn4+ (0.59%) with a tetragonal structure was prepared with the non-equivalent doping of Mn4+. The typical luminescent behaviors of Mn4+ can be observed from the phosphors. Different from the fluoride phosphors with the equivalent doping of Mn4+, K5In3F14:Mn4+ (0.59%) has a short decay time (2.74 ms). The white LED fabricated with K5In3F14:Mn4+ (0.59%) and commercial β-SiALON:Eu2+ emits bright white light under a 20 mA current, and its color gamut is up to 103% of the National Television System Committee (NTSC) standard value. So, K5In3F14:Mn4+ (0.59%) is a potential red component for LED backlighting.

Thermally Activated Delayed Fluorescence Polysiloxanes with Short Delay Fluorescence Lifetimes.

Blue-emitting thermally activated delayed fluorescence (TADF) polymers are still in demand for high-efficiency display materials. Through-space charge transfer (TSCT) strategy is promising for keeping color purity of blue-emitting polymers with nonconjugated main chains. It is, however, hard to synthesize copolymers with well-dispersed donors or acceptors utilizing traditional polyethylene backbones via radical polymerization. Herein, two series of blue-emitting polysiloxane with TADF properties, random and order-controlled copolysiloxanes, are successfully designed and synthesized and their photophysical properties are investigated and compared in detail. All of them display short prompt and delay fluorescence lifetimes and a very fast reverse intersystem crossing (RISC) rate of 107 s-1 . Compared with random copolysiloxanes, acceptors are well separated by donors for order-controlled copolysiloxanes, which exhibit the faster RISC processes and the higher photoluminescence quantum yield. Therefore, the order-controlled architecture provides a guide for improving light-emitting efficiency of TSCT-type TADF polymers.

White-Light GaN-μLEDs Employing Green/Red Perovskite Quantum Dots as Color Converters for Visible Light Communication

GaN-based μLEDs with superior properties have enabled outstanding achievements in emerging micro-display, high-quality illumination, and communication applications, especially white-light visible light communication (WL-VLC). WL-VLC systems can simultaneously provide white-light solid-state lighting (SSL) while realizing high-speed wireless optical communication. However, the bandwidth of conventional white-light LEDs is limited by the long-lifetime yellow yttrium aluminum garnet (YAG) phosphor, which restricts the available communication performance. In this paper, white-light GaN-μLEDs combining blue InGaN-μLEDs with green/red perovskite quantum dots (PQDs) are proposed and experimentally demonstrated. Green PQDs (G-PQDs) and red PQDs (R-PQDs) with narrow emission spectrum and short fluorescence lifetime as color converters instead of the conventional slow-response YAG phosphor are mixed with high-bandwidth blue InGaN-μLEDs to generate white light. The communication and illumination performances of the WL-VLC system based on the white-light GaN-based μLEDs are systematically investigated. The VLC properties of monochromatic light (green/red) from G-PQDs or R-PQDs are studied in order to optimize the performance of the white light. The modulation bandwidths of blue InGaN-μLEDs, G-PQDs, and R-PQDs are up to 162 MHz, 64 MHz, and 90 MHz respectively. Furthermore, the white-light bandwidth of 57.5 MHz and the Commission Internationale de L’Eclairage (CIE) of (0.3327, 0.3114) for the WL-VLC system are achieved successfully. These results demonstrate the great potential and the direction of the white-light GaN-μLEDs with PQDs as color converters to be applied for VLC and SSL simultaneously. Meanwhile, these results contribute to the implementation of full-color micro-displays based on μLEDs with high-quality PQDs as color-conversion materials.

Shining Mn4+ in 0D Organometallic Fluoride Hosts towards Highly Efficient Photoluminescence

AbstractThe design and discovery of Mn4+‐activated fluoride phosphors that can secure both high luminescence efficiency and short fluorescence lifetime simultaneously are crucial and urgent for constructing high‐quality wide‐color gamut (WCG) backlight display applications. Herein, a series of brand‐new Mn4+‐activated narrow‐band red‐emitting phosphors with both high external quantum efficiency (EQE, >50%) and short fluorescence lifetime (τ ≤ 3.8 ms) are designed by introducing Mn4+ into newfound tetramethylammonium (Me4N)‐based organometallic fluoride (Me4N)2BF6 (B = Ge, Ti, Zr) hosts. These intriguing properties of Mn4+ arise from the larger steric hindrance of (Me4N)+ cations and low local structure symmetry in the 0D (Me4N)2BF6, as verified by the structural and spectral analyses. (Me4N)2GeF6:Mn4+, as a representative, shows a high EQE of ≈64.6% and a short lifetime of ≈3.78 ms. A prototype projector with superb performance is assembled by employing a remote (Me4N)2GeF6:Mn4+‐based white light‐emitting diode with high luminous efficiency (≈143.09 lm W−1) and WCG (≈112.02% National Television System Committee (NTSC)) to demonstrate their great potentials for backlight applications. The research brings up a promising alternative as the host materials for Mn4+‐doped fluoride phosphors and provides a deeper understanding on the correlation between structure and luminescence.

Near-infrared photoluminescence properties of Er/Yb- and Ho/Yb-doped multicomponent silicate glass – The role of GeO2, Al2O3 and ZnO

We prepared multicomponent silicate glass, which contained components with different glass-forming abilities, such as GeO2, Al2O3 and ZnO, or different concentrations of glass-modifier oxide Na2O. The influence of the glass composition on the network structure and its effect on the photoluminescence properties of rare-earth ions were investigated. It was found that a change in the Na2O content significantly affects the network polymerisation, but its influence on the photoluminescence of RE ions is limited. The photoluminescence properties of RE ions were significantly influenced by the presence of different components, such as GeO2, Al2O3 and ZnO, which was attributed to changes in the local environment of RE ions. ZnO induced highest asymmetry of host matrix around the RE ions, which led to a strong and broad photoluminescence with short fluorescence lifetime, whereas the inclusion of Al2O3 and GeO2 led to highly symmetric matrix with narrow emission bands and longer decay.

Fluorescence lifetime imaging microscopy (FLIM) detects differences in metabolic signatures between euploid and aneuploid human blastocysts.

Can non-invasive imaging with fluorescence lifetime imaging microscopy (FLIM) detect metabolic differences in euploid versus aneuploid human blastocysts? FLIM has identified significant metabolic differences between euploid and aneuploid blastocysts. Prior studies have demonstrated that FLIM can detect metabolic differences in mouse oocytes and embryos and in discarded human blastocysts. This was a prospective observational study from August 2019 to February 2020. Embryo metabolic state was assessed using FLIM to measure the autofluorescence metabolic factors nicotinamide adenine dinucleotide dehydrogenase together with nicotinamide adenine phosphate dinucleotide dehydrogenase (NAD(P)H) and flavin adenine dinucleotide (FAD). Eight metabolic FLIM parameters were obtained from each blastocyst (four for NAD(P)H and four for FAD): short (T1) and long (T2) fluorescence lifetime, fluorescence intensity (I) and fraction of the molecules engaged with enzymes (F). The redox ratio (NAD(P)H-I)/(FAD-I) was also calculated for each image. This study was performed at a single academically affiliated centre where there were 156 discarded frozen blastocysts (n = 17 euploids; 139 aneuploids) included. Ploidy status was determined by pre-implantation genetic testing for aneuploidy (PGT-A). Discarded human blastocysts were compared using single FLIM parameters. Additionally, inner cell mass (ICM) and trophectoderm (TE) were also evaluated. Multilevel models were used for analysis. A post-hoc correction used Benjamini-Hochberg's false discovery rate, at a q-value of 0.05. Comparing euploid (n = 17) versus aneuploid (n = 139) embryos, a significant difference was seen in NAD(P)H-F (P < 0.04), FAD-I (P < 0.04) and redox ratio (P < 0.05). Euploid ICM (n = 15) versus aneuploid ICM (n = 119) also demonstrated significantly different signatures in NAD(P)H-F (P < 0.009), FAD-I (P < 0.03) and redox ratio (P < 0.03). Similarly, euploid TE (n = 15) versus aneuploid TE (n = 119) had significant differences in NAD(P)H-F (P < 0.0001) and FAD-I (P < 0.04). This study utilized discarded human blastocysts, and these embryos may differ metabolically from non-discarded human embryos. The blastocysts analysed were vitrified after PGT-A biopsy and it is unclear how the vitrification process may affect the metabolic profile of blastocysts. Our study was also limited by the small number of rare donated euploid embryos available for analysis. Euploid embryos are very rarely discarded due to their value to patients trying to conceive, which limits their use for research purposes. However, we controlled for the imbalance with the bootstrap resampling analysis. These findings provide preliminary evidence that FLIM may be a useful non-invasive clinical tool to assist in identifying the ploidy status of embryos. The study was supported by the Blavatnik Biomedical Accelerator Grant at Harvard University. Becker and Hickl GmbH and Boston Electronics sponsored research with the loaning of equipment for FLIM. D.J.N. is an inventor on patent US20170039415A1. There are no other conflicts of interest to declare. N/A.

Halogenated BODIPY photosensitizers: Photophysical processes for generation of excited triplet state, excited singlet state and singlet oxygen

We have systematically examined the formation of singlet oxygen O2(1Δg), the excited triplet state (T1), and excited singlet state (S1) for halogenated BODIPY photosensitizers (halogen = Cl, Br, and I) in eight solvents to understand how halogen atoms and solvent affect these properties. The phosphorescence spectra and lifetimes of singlet oxygen generated by these halogenated BODIPYs have been measured by steady state/time resolved NIR emission, while the formation quantum yield of singlet oxygen (ΦΔ) has been determined by chemical method using diphenylisobenzofuran (DPBF) as the trapping agent. The formation quantum yield ΦΔ of singlet oxygen can be as high as 0.96 for iodinated BODIPY and 0.71 for brominated BODIPY. The triplet state T1 absorption spectra of brominated and iodinated BODIPYs have been recorded by laser flash photolysis method, in which T1 shows high formation efficiency and long lifetime. The formation and decay of excited singlet state S1 of four BODIPYs have been measured by ground state (S0) absorption and steady state/time resolved fluorescence. The results show that larger halogen atoms on BODIPY core lead to smaller fluorescence quantum yield, shorter fluorescence lifetime and higher singlet oxygen formation quantum yield due to heavy atom effect that promotes the formation of triplet state. On the other hand, higher solvent polarity causes lower singlet oxygen formation quantum yield, smaller fluorescence quantum yield, and shorter fluorescence lifetime. This solvent effect is explained by the presence of photoinduced charge transfer (ICT) process from halogen atoms to BODIPY. The ICT efficiency has been estimated and the results are agreed with ICT theory. ICT process in halogenated BODIPYs has never been revealed in literature. HOMO/LUMO obtained from DFT calculation also supports the presence of ICT. The involvement of ICT in the photosensitizing process of halogenated BODIPYs provides new insights for designing BODIPY photosensitizers for photodynamic therapy of tumor.

Authentication of acacia honey using fluorescence spectroscopy

The potential of multiple fluorescence spectroscopy detection methods for the authentication of Robinia pseudoacacia L. honey (acacia honey) was evaluated. Fluorescence intensity (excitation wavelength: 280 nm), three-dimensional fluorescence spectra (excitation wavelengths: 200–460 nm; emission wavelengths: 260–560 nm), and fluorescence lifetime were recorded respectively to distinguish acacia honey (n = 160 samples harvested from eight regions of Shandong province in North China), concentrated acacia honey, and syrups. The fluorescence intensities, three-dimensional fluorescence spectra, and fluorescence lifetime of acacia honey, concentrated acacia honey, and syrups showed significant difference. Acacia honey samples had a higher fluorescence intensity and peak values as well as shorter fluorescence lifetime. The combination of the three fluorescence spectroscopy detection methods could easily distinguish acacia honey, concentrated acacia honey and syrups, and multiple fluorescence parameters gave advantage to distinguish adulteration of acacia honey, which represents a reliable, rapid, non-destructive, and low-cost method for authenticating acacia honey.

Hot-Band-Absorption-Induced Anti-Stokes Fluorescence of Aggregation-Induced Emission Dots and the Influence on the Nonlinear Optical Effect.

Hot-band absorption (HBA)-induced anti-Stokes fluorescence (ASF) with longer-wavelength excitation is one effective pathway to deep penetration and low autofluorescence in intravital fluorescence imaging, raising demands for fluorophores with broad spectra, high absorption, and strong emission. However, typical fluorescent dyes display some emission quenching when their concentration is increased in order to obtain brighter fluorescence. In this work, the HBA-induced ASF of aggregation-induced emission (AIE) dots is reported. BPN-BBTD dots were synthesized and confirmed with a fluorescence enhancement and a considerable ASF intensity. In addition, the mechanism of ASF and the HBA process of BPN-BBTD dots were carefully validated and discussed. To obtain the full advantages of the long-wavelength excitation and the short fluorescence lifetime in deep-tissue bioimaging, a large-depth ASF confocal microscopic imaging of in vivo cerebral vasculature was conducted under the excitation of a 980 nm continuous wave laser after intravenous injection of BPN-BBTD dots. Meanwhile, the 3D structure of the cerebrovascular network was successfully reconstructed.

Non-Interventional and High-Precision Temperature Measurement Biochips for Long-Term Monitoring the Temperature Fluctuations of Individual Cells.

Monitoring the thermal responses of individual cells to external stimuli is essential for studies of cell metabolism, organelle function, and drug screening. Fluorescent temperature probes are usually employed to measure the temperatures of individual cells; however, they have some unavoidable problems, such as, poor stability caused by their sensitivity to the chemical composition of the solution and the limitation in their measurement time due to the short fluorescence lifetime. Here, we demonstrate a stable, non-interventional, and high-precision temperature-measurement chip that can monitor the temperature fluctuations of individual cells subject to external stimuli and over a normal cell life cycle as long as several days. To improve the temperature resolution, we designed temperature sensors made of Pd–Cr thin-film thermocouples, a freestanding Si3N4 platform, and a dual-temperature control system. Our experimental results confirm the feasibility of using this cellular temperature-measurement chip to detect local temperature fluctuations of individual cells that are 0.3–1.5 K higher than the ambient temperature for HeLa cells in different proliferation cycles. In the future, we plan to integrate this chip with other single-cell technologies and apply it to research related to cellular heat-stress response.

FLGS-04. Fluorescence lifetime imaging (FLIm) is a dye-free, high sensitivity approach for fluorescence guided surgery in high-grade and low-grade gliomas

Abstract INTRODUCTION Fluorescence-guided surgery can improve tumor identification and extent of surgical resection. 5-ALA is the standard for GBM, but is limited by lack of quantitative fluorescence, a need to work in the dark, and a lack of sensitivity for low grade tumors. We have developed a novel instrument for dye-free tissue autofluorescence lifetime imaging (FLIm) to identify glioma tissue during resection. This approach utilizes time-resolved autofluorescence measurements in narrow-band channels to assess markers of tissue metabolism. Compared to intensity-based imaging of exogenous fluorophores, FLIm has greater sensitivity without dependence on background lighting. The advantages of FLIm include quantitative tissue analysis, the ability to work under full light conditions, sensitivity for high and low grade gliomas, and the potential ability to identify IDH mutational status. In this study, we validated the use of FLIm for identification of glioma tissue at tumor resection margins. METHODS FLIm was used to image tissue margins during glioma resections and compared to microbiopsies from imaged regions to correlate fluorescence with histopathology. RESULTS FLIm was applied intraoperatively to 11 GBM and 5 LGG patients (7 imaged biopsies per patient). In GBM, tumor infiltration of cortex was associated with significantly decreased fluorescence lifetime (FL) in channels 2 (470/28nm;p&amp;lt;0.05) and 3 (542/50nm;p&amp;lt;0.002). In subcortical margins, FL was inversely proportional to the density of tumor in channels 2,3 (p&amp;lt;0.05). When IDH wild-type GBMs were compared to IDH1-mutant tumors, FL was noted to be significantly longer in channel 1 (390/40nm;p&amp;lt;0.05), and trended towards longer FL in channel 2, shorter FL in channel 3. In LGG, FL was significantly correlated with tumor density in channel 2 (p&amp;lt;0.01). CONCLUSIONS FLIm is a dye-free, quantitative alternative to 5-ALA for fluorescence guided glioma resections with sensitivity to high and low-grade tumors, and the ability to predict IDH mutations in GBM. Further validation studies are on-going.

Controlled synthesis and photoluminescence behaviors of Lu2O2SO4:Eu3+ and Lu2O2S:Eu3+ phosphors

A “general” amorphous precursor that can synthesize Eu3+ doped Lu2O2SO4 and Lu2O2S phosphors was prepared from commercially available Lu2O3 (AR), HNO3 (99.95% purity), (NH4)2SO4 (AR) and NH3·H2O (99.95% purity) as raw materials via a facile co-precipitation method. Based on this, block-like Lu2O2SO4:Eu3+ phosphors were synthesized by calcination in air, and mixed structures of near-spherical and rod-like Lu2O2S:Eu3+ phosphors were synthesized by calcination in a confined sulfuration atmosphere created using a solid-state method. Studies have shown that the molar ratio of SO42−:Lu3+ and the aqueous ammonia titration volume is very important in the co-precipitation process, the optimal ratio was selected as 25:1, and the optimal 1.5 M NH3·H2O solution volume was selected as 22 mL in this study. In the subsequent calcination process, the effect of calcination temperature on the target product was studied. The optimal calcination conditions are a calcination temperature of 800 °C for 2 h in air and 500 °C for 2 h in a closed sulfuration atmosphere, respectively, for the oxysulfate and oxysulfide phosphors. The photoluminescence (PL) behavior of the two phosphors was systematically investigated. The oxysulfate and oxysulfide phosphors show the characteristic red-light emission of the Eu3+ ion at about 620 and 628 nm, respectively, which originates from the 5D0-7FJ (J = 0,1,2,4) transition of the Eu3+ ion. The luminescence quenching types of both phosphors were dominated by exchange interactions and the optimum Eu3+ molar concentrations were found to be 3.0% for Lu2O2SO4:Eu3+ and 6.0% for Lu2O2S:Eu3+. The oxysulfide phosphor had a PL intensity ∼2.15 times stronger than the oxysulfate phosphor. The CIE color coordinates of the Lu2O2SO4:Eu3+ and Lu2O2S:Eu3+ phosphors are (0.6551, 0.3444) and (0.5842, 0.413), which belong to the categories of reddish-orange and orange colors, respectively. A shorter fluorescence lifetime (∼12.650 μs) and CCT (1738 K) was observed for the oxysulfide phosphor relative to those of the oxysulfate phosphor (∼377.956 μs and 2787 K).

Conformation-dependent mechanochromic delayed fluorescence of AIE-active tetra-coordinated B–N complexes

Mechanochromic luminescence (MCL) materials have attracted great attention due to their promising prospect in mechanical sensors, optoelectronic devices and data storage. In this work, two novel molecules bearing electron deficient tetra-coordinated phenylpyridine boron (PPYB) and electron donating phenothiazine (PTZ) are developed, and their thermal stability, optical and electronic structures, electrochemical property, photophysical property and MCL behaviors are investigated. Both molecules display obvious MCL effect with large emission color change from blue to yellow, which are ascribed to the changes of molecular conformation from quasi-axial conformation to quasi-equatorial one. In quasi-axial conformation, they show short fluorescence lifetimes without obvious delayed components, but in quasi-equatorial conformation, they have longer fluorescence lifetimes with prominent delayed components. Moreover, they are weakly fluorescent in solutions, but the emission intensity and delayed components are significantly enhanced in the solid state, demonstrating typical aggregation-induced delayed fluorescence (AIDF) characteristics. The application of both molecules as emitters in organic light-emitting diodes (OLEDs) is also evaluated.

CsPb(Br/I)3 Perovskite Nanocrystals for Hybrid GaN-Based High-Bandwidth White Light-Emitting Diodes

The modulation bandwidth of white light emitting diodes (LEDs) is an important factor in visible light communication (VLC) system, which is mainly limited by the down-conversion materials. The broad spectrum and long lifetime of conventional light conversion materials represent an obstacle to future technological developments. Here, we show that inorganic semiconductor perovskite nanocrystals offer a promising alternative nanomaterial. Anion exchange between different perovskite nanocrystals by post-synthesis is a highly efficient protocol to tune the chemical composition and optoelectronic properties of lead halide perovskite nanocrystals. The fine-tuning of the nanocrystal fluorescence is achieved by 2 blending colloidal solutions of CsPb(Br/I)3 lead halide perovskites with different content of halide. The tunable optical emission and short fluorescence lifetime (< 5 ns) of the nanocrystals are exploited to realize white LEDs with a high modulation bandwidth (0.7 GHz), offering a potential route towards fast, energy efficient visible light communication.

LONGITUDINAL FOVEAL FLUORESCENCE LIFETIME CHARACTERISTICS IN GEOGRAPHIC ATROPHY USING FLUORESCENCE LIFETIME IMAGING OPHTHALMOSCOPY.

Short foveal fluorescence lifetimes (fFLT) in geographic atrophy are typically found in eyes with foveal sparing (FS) but may also occur in eyes without FS. We investigated whether short fFLT could serve as a functional biomarker for disease progression in geographic atrophy. Thirty three eyes were followed over the course of 4 to 6 years. Foveal sparing was assessed using fluorescence lifetime imaging ophthalmoscopy, optical coherence tomography, fundus Autofluorescence, and macular pigment optical density. Eyes with FS exhibited shorter fFLT compared with eyes without FS. Short fFLT (<600 ps) were measured in all eyes with FS and half of the eyes without FS. Eyes with FS showed a bigger increase in fFLT per year (+39/+30 ps (short spectral channel/long spectral channel) in FS versus +29/+22 ps (short spectral channel/long spectral channel) in non FS). The best-corrected distance visual acuity correlated significantly with fFLT (P = 0.018 and P = 0.005 for short spectral channel/long spectral channel). Macular pigment optical density measurements correlated significantly with fFLT but not in all spectral channels (P ranging from 0.018 to 0.077). In geographic atrophy, shorter fFLT are associated with FS but they can also be observed in eyes without FS. Our longitudinal data suggest that shorter fFLT features in eyes with loss of FS represent an earlier stage of disease and may be more prone to loss of the visual acuity.

Local structure and luminescent properties of Cs2KGaF6:Mn4+ phosphor for backlight white LEDs

Narrow-band red-emitting phosphors are worth investigating and developing to enhance their luminescence efficiency for white light-emitting diodes (WLEDs) and broaden the color gamut of backlight displays. Herein, a novel red-emitting fluoride phosphor Cs2KGaF6:Mn4+ (CKGFM) was synthesized, which presents sharp red emission bands, short fluorescence lifetime (τ = 3.81 ms) and high external quantum efficiency (EQE = 43%). To better understand Mn4+ incorporation in CKGFM, density functional theory (DFT) energetic calculations were performed to compare the charge compensation probabilities of an Mn4+ substituted at a Ga3+ or K+ site. The temperature-dependent luminescence trend shows that the CKGFM phosphor has good thermal stability in the temperature range of 15–120 ℃, indicating its potential in backlight LEDs. The as-prepared CKGFM phosphor was used to fabricate one white light-emitting diode (WLED) with β-SiAlON:Eu2+ green phosphor and blue InGaN LED chip, which shows a high luminous efficiency of 106.30 lm∙W−1 and a National Television Standards Committee (NTSC) value of 114.6%. The present study provides detailed insights into the local structure of Mn4+ substituted in fluoride red-emitting phosphors and helps to realize better Mn4+ emission for WLEDs.