Strong Green Emission Research Articles

Mid-Infrared, Green and Red Emission in Ho3+ - Er3+ Co-Doped Phosphate Glasses

Over the past decades, phosphate glasses show ample advantages in laser technology because of their excellent optical properties like a low glass transition temperature, low phonon energy, large infrared transmission window, and high gain density. The inclusion of lead and alkali earth metals to these phosphate glasses also improves the chemical durability of glasses, which have more advantages in smart cards, medical applications, and micro-batteries. The optimum environment for chemical durability and incorporating rare earth ions can be achieved by the interaction between sulphate and phosphate ions. Moreover, phosphate glasses mixed with alkali sulphate provides scope for micro battery applications. The presence of network modifiers like Pb2+, Zn2+ in phosphate glasses introduces structural modifications and increases the number of non-bridging oxygens (NBOs) in glass network. The metal oxides like PbO, Bi2O3 makes phosphate glass suitable for rare earth ion incorporation by softening the glass and provides better distribution by controlling the formation of clusters. The wide variety of rare earth ions in the phosphate glasses leads to wide range of applications in optoelectronic devices.To overcome the difficulty associated with lack of a useful absorption band at 980 nm of Ho3+ ion (easy excitation by commercial laser diode (LD)), rare earth ions such as Tm3+, Yb3+, and Er3+ can be introduced. Especially, among them, Er3+ exhibit strong absorption at 980 nm. Due to the narrower energy gap between Er3+: 4I13/2 and Ho3+: 5I7 states, the emission of Ho3+ ions can be enhanced by addition of Er3+. So, the Er3+/Ho3+ co-doped glasses have promising applications in mid-infrared (MIR) laser applications with 980 nm LD. In view of this, the set of the Er3+/Ho3+ co-doped sodium-sulfo lead phosphate glasses was prepared with the molar composition of (20-x-y) Na2SO4-20PbO-60P2O5-xEr2O3-yHo2O3 (x=0.5, y= 0.2, 0.4, 0.6, 0.8, 1.0 mol %) named as GEH-y glass and coded as GExHy. To explore various possible applications, all prepared glasses are characterised by EDS, XRD, FTIR, absorption, photoluminescence and lifetime profiles. All results are computed and few of them are compared with other glasses.We present results focused on both mid infrared and visible emission properties of Er3+/Ho3+ions in sodium-sulfo lead phosphate (GExHy) glasses. These materials exhibit simultaneously DC (down-conversion) and UC (up-conversion) photoluminescence (PL) by excitation at 379 nm and 980 nm. The favourable concentration of Ho2O3 was estimated from the analysis of NIR PL spectra for Ho3+: 2.0 mm and Er3+: 1.5 mm. In GExHy glasses, the increase in intensity near 2.0 mm with decrease in intensity at 1.5 mm infers to energy transfer process between Er3+ and Ho3+ ions.Under lexc= 379 nm the Er3+ ions are pumped to the 4G11/2 excited state and depopulate {via multi phonon relaxation MPR1} at lower 4S3/2, 2H11/2, and 4F9/2 levels and then relaxed to the 4I15/2 ground state by emitting weak and strong green emission bands along with weak red emission related to 4S3/2→4I15/2 (522 nm), 2H11/2→4I15/2 (544 nm), and 4F9/2→4I15/2 (657 nm) transitions, respectively. The up-conversion energy transfer (ET) analysis with 980 nm LD excitation, undergoes the following mechanism: Ground state absorption (GSA) : Er: 4I15/2 + hν → Er: 4I11/2 Excited State Absorption (ESA1) : Er: 4I11/2+ hν → Er: 4F7/2 Excited State Absorption (ESA2) : Er: 4I13/2 +hν → Er: 4F9/2 CR1 (Cross Relaxation) : Er: 4I11/2+Ho: 5I6→ Er: 4I15/2+Ho: 5F4 CR2 (Cross Relaxation) : Er: 4I13/2+Ho: 5I6→ Er: 4I15/2+Ho: 5F5 ET1: Er: 2S3/2+Ho: 5I8→ Er: 4I15/2+Ho: 5S2+5F4 ⇒ Ho: 5S2+5F4 → 5I8 (545 nm) ET2 : Er: 4F9/2+Ho: 5I8→ Er: 4I15/2+Ho: 5F5 ⇒ Ho: 5F5→5I8 (659 nm) MPR2: Ho: 5S2+5F4 → 5F5 ET3: Er: 4I11/2+Ho: 5I8→ Er: 4I15/2+Ho: 5I6 ⇒ Er: 4I13/2 → 4I15/2 (1554 nm) ET4: Er: 4I13/2+Ho: 5I8→ Er:4I15/2+Ho Fig. 1 Schematic energy level diagram of GE0.5H0.8 glass.The maximum energy transfer efficiency of GExHy samples is 75.5% and with the increase of Ho3+ ions, the lifetime decay has been reduced from 5.06 ms to 1.24 ms. The absorption and stimulated emission cross-sections of Er3+:1.5 mm and Ho3+: 2.0 mm were calculated. Moreover, the FWHM × σemi was estimated for Ho3+:5I7→5I8 transition to estimate the probable MIR laser emission. The CIE color coordinates were estimated from both DC and UC PL spectra. All the results indicated that the prepared GExHy glasses have promising material applications in mid-infrared solid-state lasers and telecommunications. In addition, efficient green and red emission makes these glasses attractive for the phosphor applications. Figure 1

Controllable synthesis of Tb-based metal–organic frameworks as an efficient fluorescent sensor for Cu2+ detection

A series of Tb-based metal–organic frameworks (Tb-MOFs) were successfully synthesized by a solvothermal method. The size and morphology of the as-obtained Tb-MOFs can be effectively controlled via regulating the experimental conditions such as the volume fraction of DMF and the molar ratio of Tb3+ to NaOH. It is found that all the samples exhibit strong green emissions under ultraviolet excitation, corresponding to 5D4 → 7FJ transitions of Tb3+. Interestingly, Tb-MOFs displayed an efficient and distinct luminescence quenching by Cu2+ in aqueous solutions. The competitive fluorescence detection experiments indicate that these Tb-MOFs sensors can be used as a high selective and sensitive sensor of Cu2+ detection with the detection limit of 10 µmol·L−1, which can be used as a promising fluorescence sensor for Cu2+ detection in daily life.

Highly luminescent CH3NH3PbBr3 quantum dots with 96.5% photoluminescence quantum yield achieved by synergistic combination of single-crystal precursor and capping ligand optimization

Inorganic–organic lead halide perovskite quantum dots (PQDs) are promising for application in a wide range of optoelectronic devices due to their high photoluminescence quantum yield (PLQY), tunable band gap, and narrow emission width. Despite intense research effort being devoted to the synthesis of highly luminescent PQDs, the achievement of defect-mediated low PLQY is still challenging. For PQDs processed by the well-known ligand-assisted reprecipitation technique, defects are inevitably formed on the surface, possibly due to the highly ionic precursor solution containing disordered elemental ions. To overcome this problem, in this work, CH3NH3PbBr3 single crystals with low defect densities were prepared using the inverse temperature crystallization method and were applied as sources for PQDs. Furthermore, capping ligands with different alkyl chain lengths were utilized to reprecipitate uniform and stable PQDs. Through the synergistic effect achieved by the use of the single-crystalline precursor and capping ligand optimization, we achieved a near-unity PLQY of 96.5% and a strong green emission. In addition, the obtained highly luminescent PQDs displayed few metallic Pb surface defects and reduced Stokes shifts that will be beneficial for future device applications.

An all-graphene quantum dot Förster resonance energy transfer (FRET) probe for ratiometric detection of HE4 ovarian cancer biomarker

Ovarian cancer (OVC), the most lethal form of all gynecological cancers, is a big threat to women’s health. Late diagnosis at the advanced stages is one of the major reasons for the ovarian cancer-related deaths. Conventionally, the up-regulated proteins CA125 (cancer antigen 125) and HE4 (human epididymis protein 4) are used as biomarkers to diagnose the OVC malignancies. The lack of sensitivity/specificity and the false-positive results create complexity in the diagnostic process. With specificity over 90 %, HE4 is suitable for diagnosing ovarian cancer. Herein, we have developed an ultrasensitive all-graphene quantum dot (GQD) Förster resonance energy transfer (FRET) probe for the ratiometric detection of HE4 biomarker. A set of two GQD samples were solvothermally prepared and then analyzed by the morphological, structural, and photophysical characterization. One GQD sample exhibited a strong green emission, peaked at around 515 nm, while the other GQD sample displayed a strong red emission with maximum at around 615 nm. The good spectral overlap between the emission and excitation spectra of the green and red GQDs, respectively, all allowed us to consider them for the design of FRET-based probe. The green and red-emitting GQDs were conjugated with HE4 antibody and used as donor and acceptor, respectively for the ratiometric sensing of HE4 ovarian cancer biomarker. The all GQD FRET probe was able to detect as low as 4.8 pM, along with a large dynamic detection range up to 300 nM. The selectivity and interference effect of the developed FRET probe was also investigated against different protein combinations.

Upconversion Luminescence, Laser Heating Effect and Temperature Sensing Properties of β-BiNbO4:Er3+/Yb3+

Upconversion (UC) phosphors of β-BiNbO4:Er3+/Yb3+ as temperature sensing materials were synthesized using the solid-state method. The structure was characterized by x-ray diffraction (XRD), revealing that all samples exhibited a single triclinic phase. Upon 980 nm laser excitation, the phosphors exhibited strong green emission and relatively weak red emission. Its possible luminescence mechanism is discussed based on the dependence of the UC emission spectra on the pump laser power. Finally, its temperature sensing properties were investigated using the temperature-dependent fluorescence intensity ratio (FIR) of two green emission bands originating from Er3+ ions. The thermal effect from laser irradiation and its influence on temperature sensing were also studied. Its absolute sensitivity SA exhibited a smaller change above 300 K, and reached a maximum value of 5.5‰ K−1 around 400 K. These results indicate that this type of qualified UC phosphor shows potential application in optical temperature sensors, especially at high temperature.

Effects of Bi3+ on down-/up-conversion luminescence, temperature sensing and optical transition properties of Bi3+/Er3+ co-doped YNbO4 phosphors

A series of YNbO4:Bi3+ and YNbO4:Bi3+/Er3+ phosphors were prepared by a conventional high temperature solid–state reaction method. The results of XRD and Rietveld refinement confirm that monoclinic phase YNbO4 samples are achieved. The down-/up-conversion luminescence of Er3+ ions was investigated under the excitation of ultraviolet light (327 nm) and near infrared light (980 nm). Under 327 nm excitation, broad visible emission band from Bi3+ ions and characteristic green emission peaks from Er3+ ions are simultaneously observed, while only strong green emissions from Er3+ ions are detected upon excitation of 980 nm. Remarkable emission enhancement is observed in down-/up-conversion luminescence processes by introducing Bi3+ ions into Er3+-doped YNbO4 phosphors. Pumped current versus up-conversion emission intensity study shows that two-photon processes are responsible for both the green and the red up-conversion emissions of Er3+ ion. Through the study of the temperature sensing property of Er3+ ion, it is affirmed that the temperature sensitivity is sensitive to the doping concentration of Bi3+ ions. By comparing the experimental values of the radiative transition rate ratio of the two green emission levels of Er3+ ions and the theoretical values calculated by Judd-Ofelt (J-O) theory, it is concluded that the temperature sensing property of Er3+ ions is greatly affected by the energy level splitting.

Electron beam-induced preparation of AIE non-woven fabric with excellent fluorescence durability

Polymers with aggregation-induced emission (AIE) characteristics have attracted much attention because of their potential applications in luminescent self-assembling, anti-counterfeiting, decoration, and photoelectric devices. To date, most technologies to prepare fluorescent polymers lack versatility; moreover, the resultant material exhibits intrinsic defects of poor fluorescence intensity and durability. Herein, we covalently anchored units of tetraphenylethylene (TPE), an archetypal AIE luminogen, on the surface of conventional polymer fibers such as polyethylene/polypropylene nonwoven fabric (PE/PP NWF) via radiation-induced graft polymerization (RIGP) and subsequent chemical modification for the first time. The physicochemical properties of the original and modified fabrics were characterized in detail by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), wide-angle X-ray diffraction (WAXD), and thermogravimetric analysis (TGA). The results indicated that the TPE units were covalently and uniformly anchored on the surface of PE/PP NWF with a disordered architecture and that the as-prepared fluorescent fabric had a high thermal stability. Additionally, the fluorescent properties of the as-prepared fluorescent fabric were measured. It emitted a strong green emission and showed superior fluorescence durability after 20 cycles of accelerated laundering or in 12 M concentrated HCl and NaOH solutions.

N-doped carbon dots modified with the epithelial cell adhesion molecule antibody as an imaging agent for HepG2 cells using their ultra-sensitive response to Al3+

Carbon dots (CDs) are emerging as an ideal multifunctional materials due to their ease of preparation and excellent properties in medical imaging technology, environmental monitoring, chemical analysis and other fields. N-doped CDs modified with the epithelial cell adhesion molecule antibody (anti-EpCAM-NCDs) were synthesized in an ingenious and high-output approach. Due to the fluorescence enhancement effect of the introduced N atoms, the obtained anti-EpCAM-NCDs exhibited a strong green emission with an absolute quantum yield of up to 32.5%. Anti-EpCAM-NCDs have immunofluorescent properties and an active targeting function. The fluorescence effect and fluorescence quenching of anti-EpCAM-NCDs are used to image cells and detect Al3+, respectively. Experimental results show that this probe exhibited a wide linear response to Al3+ over a concentration range of 0−100 μM with a detection limit and quantification limit of 3 nM and 6 nM, respectively. Significantly, anti-EpCAM-NCDs, which have negligible cytotoxicity, excellent biocompatibility and high photostability, could be used for the intracellular imaging of HepG2 cells and the detection of Al3+ in environmental and biological samples. As an efficient multifunctional material, anti-EpCAM-NCDs hold great promise for a number of applications in biological systems.

Color tunable cathodoluminescence properties of RE2WO6:Ln3+ (RE, Ln = Er3+ and Tm3+) phosphor and its microscopic imaging

Highly crystalline RE2-xWO6:xLn3+ (RE, Ln = Er3+ and Tm3+, x = 0.02 to 0.50 mol.) phosphors were successfully synthesized by the solid-state reaction method. The cathodoluminescence (CL) properties of the RE2-xWO6:xLn3+ phosphors were studied in detail by changing the Ln3+ (Er, Tm) doping concentration, accelerating voltage and tuning the electron beam current. The CL spectra of the undoped Er2WO6 phosphor showed bright red emission due to the 4F9/2→4I15/2 (Er3+) transition, while Tm3+ doped Er2WO6 display the strong green emission due to 4S3/2→4I15/2 (Er3+) transitions. The Er3+ doped Tm2WO6 phosphor showed strong white light emission due to the combination of several bands in the CL spectra. The CL emission intensity of the phosphors linearly enhanced when the electron beam current was increased from 1.00 nA to 7.0 nA and no saturation emission was noted in this range. The Commission Internationale del’Eclairage chromaticity coordinates were measured for the RE2WO6:Ln3+ phosphors.

Synthesis of Yb3+/Ho3+ co-doped Y2O3 nanoparticles and its application to dye sensitized solar cells

In this study, a series of Yb3+/Ho3+ co-doped Y2O3 up-conversion (UC) nanophosphors was fabricated by a homogeneous precipitation method. The photoluminescence emission in the visible regions of the nanophosphors has been investigated under 980 nm IR laser excitation. The nanophosphors exhibited strong visible green and weaker red up-conversion emissions. The effects of various concentrations of Yb3+ (1–4 mol%) on the photoluminescence properties of fabricated nanophosphors was also investigated. The fabricated UC nanophosphors were incorporated in the DSSC and their influence on the photovoltaic performance of the DSSC was characterized by a current-voltage curve, and incident photon to current conversion efficiency. Compared with the DSSC without the UC nanoparticles which had a cell efficiency of 4.27%, the DSSC incorporating Y2O3:Ho3+/ Yb3+ UC nanoparticles showed an enhanced cell efficiency of 4.79%.

Luminescence behaviour of the synthesized erbium and thulium co-doped potassium, sodium, lithium or rubidium yttrium double tungstate nanopowders

Nanocrystalline M I Y(WO 4 ) 2 double tungstates (M I = Li, Na, K and Rb) co-doped with Er 3+ and Tm 3+ ions were synthesized by hydrothermal and Pechini techniques and characterised by means of X-ray diffraction, infrared absorption and electron absorption spectra. Their emission spectra and luminescence decay kinetics were recorded at ambient temperature. These investigations were focused on impact of structural changes and morphology inducing by the alkaline ion on the Er ↔ Tm energy transfer efficiency in the studied nanocrystalline oxide systems. The effect of the thermal treatment on morphology and spectroscopic properties of the synthesized nano-materials was studied. Furthermore, emission spectra attained under different excitation as well as study on luminescence decay curves made it possible to determine the differences and dynamics of feeding and relaxation of excited states involved in luminescence phenomena. The energy transfer mechanism between Er 3+ and Tm 3+ ions was proposed and analysed in terms its usefulness in the phosphors and optical amplifiers operating at 1.8 μm. • Li/Na/K/RbY(WO 4 ) 2 :Er 3+ ,Tm 3+ were synthesized by the Pechini and hydrothermal method in the nanocrystalline form. • Structural properties were characterised by the X-ray diffraction (XRD) and infrared spectroscopy. • Strong green emission of Er 3+ ions located at 525 and 550 nm is observed for all compounds. • The lowest intensity of this emission is observed for lithium compounds. • The efficient energy transfer from erbium to thulium takes place in KY(WO 4 ) 2 :Er 3+ ,Tm 3+ sample.

Size-tunable β-NaYF4:Yb/Er up-converting nanoparticles with a strong green emission synthesized by thermal decomposition

Abstract Size-tunable β-NaYF4: Yb/Er (50–400 nm) up-converting nanoparticles (UCNPs) with a strong green emission were successfully prepared by a facile thermal decomposition method in a short period of time. The effects of the reaction time, the oleic acid (OA) content, and the doped Gd3+ concentration on the crystal structure, the size evolution mechanism and the luminescence mechanism of the β-NaYF4: Yb/Er nanoparticles were discussed in detail. Characterization was completed using X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution (HR-TEM), scanning electron microscopy (SEM), and photoluminescence (PL). The results reveal that the phase transition was completed at 15 min and the morphology of the NaYF4: Yb/Er UCNPs changed from spherical to large hexagonal disks (200–400 nm) in non-doped Gd3+. An appropriate decrease in the volume ratio of oleic acid (OA) to 1-octadecene (ODE) promoted NaF production, resulting in the formation of the hexagonal phase crystals and the subsequent increase of luminous intensity by 30–40 times. More importantly, the size of the β-NaYF4: Yb/Er decreased with Gd3+ doping, and the UCNPs ultimately transformed into small hexagonal prisms (50 nm) with high monodispersity when the doping concentration of Gd3+ was 60 mmoL. The PL spectra confirmed that the luminous intensity of the UCNPs with doped Gd3+ was much higher than that of the undoped UCNPs. The results show that this route for UCNP fabrication with high luminous efficiency and a small size could be extended to other UCNP systems for multifunctional biomedical applications.

Synthesis and Photocatalytic Activity of β-Ga2O3 Nanostructures for Decomposition of Formaldehyde under Deep Ultraviolet Irradiation

An attempt to degrade volatile organic compounds (VOCs) and sterilize air simultaneously is highly desirable to improve indoor air quality. With the help of deep ultraviolet (UVC) lighting, harmful bacteria that exists in the air can be destroyed. Thus, a new photocatalytic substance that can break down VOCs under UVC irradiation is required. Here, we demonstrate the photocatalytic activity of β-Ga2O3 nanostructures, synthesized via the solvothermal method for removing formaldehyde (HCHO) under deep ultraviolet irradiation. The Raman and XRD results indicated that as-synthesized nanostructures showed β-crystalline phase with a monoclinic structure. The photoluminescence spectrum exhibited a broad and strong green emission peak at 510 nm, which was likely attributed to a considerable amount of oxygen and gallium vacancies formed during the calcinating process. The photocatalytic efficiency for decomposing HCHO at room temperature under deep ultraviolet irradiation (278 nm) of the synthesized β-Ga2O3 nanoparticles is higher than that of the β-Ga2O3 nanorods. Both nanoparticles and nanorods obeyed the pseudo-first-order Langmuir-Hinshelwood kinetic model with a degradation rate constant of 0.057 and 0.033 min−1, corresponding to the efficiency of 82% and 62% in the formaldehyde removal, respectively.

Structural and optical characterization of Er-doped CaMoO4 down-converting phosphors.

xEr2O3-(1-x)CaMoO4 (x = 1, 3, 5, 7 and 10 mol%) nanoparticles were synthesized by solid-state sintering at 800°C. X-ray diffraction studies confirmed the tetragonal crystal structure of CaMoO4, while the doped samples show the co-existence of cubic Er2O3 and tetragonal CaMoO4 and rule out the replacement of Ca2+ by Er3+ in the structure. The crystal unit-cell dimensions, phase concentration and atomic position coordinates were determined by Rietveld refinement. The short-range structure of CaMoO4 consists of tetrahedral MoO4 and snub disphenoid deltahedral CaO8 units, while the unit cell of Er2O3 consists of two types of ErO6 octahedral units. All MoO4 units contain Mo-O bonds of equal lengths, whereas two types of slightly different Ca-O bond lengths exist in CaO8. Raman spectra of the doped samples show only Mo-O vibrational modes and the Raman peaks of Er2O3 are masked by Mo-O bond vibrations. CaMoO4 shows bluish-green emission at 500 nm, while Er-doped samples show strong green emission under UV excitation. UV irradiation (380 nm) induces down-conversion green emission at 531 nm and 552 nm and good color purity in 1 mol% Er2O3-CaMoO4 sample which makes it a potential candidate for applications in optical devices.

Machine-Learning-Driven Synthesis of Carbon Dots with Enhanced Quantum Yields.

Knowing the correlation of reaction parameters in the preparation process of carbon dots (CDs) is essential for optimizing the synthesis strategy, exploring exotic properties, and exploiting potential applications. However, the integrated screening experimental data on the synthesis of CDs are huge and noisy. Machine learning (ML) has recently been successfully used for the screening of high-performance materials. Here, we demonstrate how ML-based techniques can offer insight into the successful prediction, optimization, and acceleration of CDs' synthesis process. A regression ML model on hydrothermal-synthesized CDs is established capable of revealing the relationship between various synthesis parameters and experimental outcomes as well as enhancing the process-related properties such as the fluorescent quantum yield (QY). CDs exhibiting a strong green emission with QY up to 39.3% are obtained through the combined ML guidance and experimental verification. The mass of precursors and the volume of alkaline catalysts are identified as the most important features in the synthesis of high-QY CDs by the trained ML model. The CDs are applied as an ultrasensitive fluorescence probe for monitoring the Fe3+ ion because of their superior optical behaviors. The probe exhibits the linear response to the Fe3+ ion with a wide concentration range (0-150 μM), and its detection limit is 0.039 μM. Our findings demonstrate the great capability of ML to guide the synthesis of high-quality CDs, accelerating the development of intelligent material.

Construction of Supramolecular Organogel with Circularly Polarized Luminescence by Self-Assembled Guanosine Octamer

SUMMARYGel formation using guanosine self-assembly is an important process in supramolecular chemistry. Here, we report the stepwise construction of circularly polarized luminescent supramolecular organogels from self-assembled guanosine quadruplexes. A lipophilic guanosine derivative (aldG) is designed and synthesized for the formation of a well-defined G8-octamer. The diamine linkers are used to connect G8-octamer units by imine formation to facilitate the construction of the supramolecular gel networks. 1H NMR experiments show that the pre-assembled aldG8-octamer remains intact and is crucial for transparent and stiff organogel formation. With extended conjugation, the aldG organogels exhibit strong green fluorescence emission and circularly polarized properties without the assistance of any external fluorescent dyes, suggesting an alternative approach to construct molecular probes for biological and material applications.

Structurally-thrifty and visible-absorbing fluorophores.

Fluorophores with a minimal push-pull backbone are actively pursued due to their potentials in biological labelling. Herein a series of structurally-thrifty and visible-absorbing fluorophores (SDXs) were successfully constructed following the D'D-π-A design strategy, in which a secondary donor (D') was introduced in conjugation with the donor (D) to enhance its electron donating capability. For a very small scaffold, SDXs exhibit a surprisingly long-wavelength absorption band in the visible spectral range (λabs=420nm) and a strong green fluorescence emission (λem=530nm) with a fluorescence quantum yield up to 0.84. Notably, fluorescence of SDXs was quenched in hydrogen-bonding solvents, e.g. MeOH and H2O. This phenomenon renders SDXs feasibility for imaging of cellular non-hydrogen-bonding microenvironment, as demonstrated with BEAS-2B cells. These results proved that the D'D-π-A is a powerful design strategy to construct novel structurally-thrifty fluorophores.

Charge carrier trapping processes in un-doped and BaAl2O4:Eu3+ nanophosphor for thermoluminescent dosimeter applications

The thermoluminescence (TL) mechanism for un-doped and europium (Eu3+) doped barium aluminate (BaAl2O4) were investigated and the location of energy levels for electrons/holes traps were determined in the aluminate for TL dosimetry applications. The solution combustion technique was used to synthesize the un-doped and Eu3+ doped BaAl2O4 nanopowders. X-ray diffraction showed a hexagonal crystal structure with the space group P63. The average crystallite size were found to be 50 nm and between 41 and 61 nm for un-doped and doped samples. Scanning electron microscopy showed irregular spherical and needle shapes for the un-doped and doped samples. The Kubelka–Munk function was used to calculate the optical bandgap values of 5.47 and 5.26 eV, for the un-doped and doped samples, from the diffuse reflectance spectra. The fitted x-ray photoelectron spectroscopy data demonstrated that Ba occupied two different sites, Ba1 and Ba2. Time-of-flight secondary ion mass spectroscopy in spectral mode showed the formation of the crystal lattice with the presence of the dopant. The photoluminescent and cathodoluminescent spectra were characterized by the 5D0-7FJ transitions (J = 1, 2, 3, 4) of Eu3+ with the dominate emission obtained at J = 2. A strong TL glow curve with peaks at 397 and 453 K were observed for the un-doped and doped nanopowders after irradiation with γ-rays. The doped nanopowders showed the highest TL intensity because doping with Eu3+ lead to the formation of additional trapped electrons and holes. The un-doped sample showed strong green (546 nm) TL emission due to the presence of a Vk3+ center. Whereas the Eu doped nanopowders exhibited strong TL emission at 615 nm.

Synthesis of Green Emitting Multi‐substituted Dibenzodioxins and Related Heteroacenes and Computational Investigation of Substituent Effects on Emission Spectra

AbstractPush‐pull dibenzodioxins with electron withdrawing and donating groups were prepared in good yields through a short and simple synthesis. Strong green emission above 500 nm occurs in those derivatives where there is maximum charge transfer to the most electron deficit terephthalonitrile ring, from proximal cyclic amino donor groups. Theoretical calculations support experimental findings through evaluation of excited state properties. In molecules with a nitro group, the excited state localizes electron density exclusively onto it and twisted nitro geometry was also found. In effect, electronic charge cannot relocate into the molecular plane, rendering them non‐fluorescent. Also, studies on the fluorescent derivatives show that best emission would occur when the donor moiety contains a saturated cyclic amino ring and the amines are 2°. Overall, our study establishes structure‐property guidelines and limits on dibenzodioxin functionalization towards preparing fluorescent derivatives of the same.

Three-dimensional homochiral coordination polymers of Eu(III) and Tb(III): Synthesis, structure determination, and optical properties

Self-assembly of the corresponding europium and terbium salts with designed chiral ligand (S)-5-((2-carboxy-5-oxopyrrolidin-1-yl)methyl)isophthalic acid (H3L) generated two novel 3D coordination polymers {[Eu(L)]·0.5CH3CN}n (1) and {[Tb(L)]·0.5CH3CN}n (2). Single-crystal X-ray diffraction analyses reveal that 1 and 2 are isostructural metal-organic frameworks built from four-stranded helixes. Complexes 1 and 2 are intriguing homochiral porous architectures with 6,6-connected (48∙66∙8)(413∙62) topology, whose homochirality was further confirmed by their solid-state circular dichroism spectra. Thermal analyses disclose that the desolvated frameworks of 1 and 2 can maintain their structural stability below 370 ​°C. Solid-state photoluminescence studies show that 1 and 2 exhibit strong characteristic Eu(III) and Tb(III) emissions with long lifetimes of 1.31 and 1.35 ​ms, respectively. In addition, 1 and 2 also exhibit significant second harmonic generation activities with their intensities of about 0.29 and 0.31 times larger than that of potassium dihydrogenphosphate, respectively. Very importantly, the excellent thermostabilities and strong red and green emissions of 1 and 2 are of great significance for further exploration of their applications in optical devices.