Luminescence Behavior Research Articles

The two-stepwise luminescent switching properties of triple-stimuli-responsive platinum(II) complexes bearing 4,4′-bis(2-phenylethynyl)-2,2′-bipyridine ligand

Three new square-planar platinum(II) complexes, Pt(PhC≡CbpyC≡CPh)(C≡CC6H4-X-2)2 [PhC≡CbpyC≡CPh = 4,4′-bis(2-phenylethynyl)-2,2′-bipyridine; X = F(1), Cl(2), and Br(3)] were synthesized and characterized. Upon exposure of the ground sample to volatile organic compound (VOC) vapors, a series of metastable structures of three complexes, including yellow solvent-free species 2 and 3, orange species 1, 2·ClCH2CH2Cl and 3·ClCH2CH2Cl, red species 1·1.5(CHCl3), 2·½(CH2Cl2), 2·½(ClCH2CH2Cl), 3·½(Toluene), and 3·½(ClCH2CH2Cl) were isolated. All three complexes exhibit vapor-, thermo-, and mechanical-grinding-triggered triple-stimuli-responsive luminescent switching properties. More interestingly, upon exposure to ClCH2CH2Cl vapor, the red species 2·½(CH2Cl2) or 3·½(Toluene) undergo an unusual time-dependent two-stepwise luminescent switching process and convert to the orange species 2·ClCH2CH2Cl or 3·ClCH2CH2Cl via intermediate 2·½(ClCH2CH2Cl) or 3·½(ClCH2CH2Cl). Furthermore, 1·1.5(CHCl3) also displays a two-stepwise thermoluminescent property and is transformed into orange species 1via intermediate 1·⅛(CHCl3). Furthermore, both 2 and 3 present the irreversible vapochromic and vapoluminescent properties as the yellow and orange species could not be converted to each other or transformed to the red species by absorbing the corresponding VOC vapors. Systematic studies revealed that the vapor-, thermo-, and mechanical-grinding-triggered triple-stimuli-responsive luminescence switching properties of 1–3 are due to the structural conversion and resultant changes of the lowest-energy excited states. The crystal structure, 1H NMR, luminescence spectra and PXRD measurements demonstrate that the two-stepwise luminescent switching behavior of complexes are associated with the stacking structure of species with same kind and different amount of solvent molecule. The irreversible vapoluminescent property of 2 and 3 are most likely due to the closed stacking of species which prevent the inserting of solvent molecules into the crystal lattice. In addition, complexes 1–3 have good application prospects in the visual identification of CHCl3, CH3CN and 1,2-dichloroethane vapors.

High solid-state CPL active materials based on chiral BINOL-dicyanodistyrylbenzene

Herein, we synthesized a pair of aggregation-induced emission (AIE) chiral fluorescence materials (R/S-BIN-Cyn enantiomers). The enantiomers were constructed by connecting a typical AIE molecule to a chiral 1,1′-bi-2-naphthol (BINOL) with ether linkages. The obtained enantiomers exhibited excellent AIE properties and unique state circularly polarized luminescence (CPL) behavior. Specifically, the enantiomers were CPL-active in the solid film with a high glum value of −1.1 × 10−1/+1.2 × 10−1. The CPL and circular dichroism (CD) spectra showed that chirality transfer was achieved from the chiral BINOL to the achiral AIE molecule. The present study is expected to provide a new perspective for preparing chiral luminescent devices with solid-state CPL active.

Luminescence behavior of colloid quantum dots in the presence anthracycline antibiotic mitoxantrone: Surface interaction and luminescence quenching, size and composition dependence, potential for clinical study

The luminescence of colloidal quantum dots (QDs) is often affected by the passivating layer, the stabilizing ligand, and the interactions in solution. The anthracycline antibiotic mitoxantrone (MTX) effectively quenches QDs luminescence while attaching to their surface in the aqua colloid. Careful selection of the architecture of QDs with significant luminescence quenching in the presence of MTX will make future for developing a simple and fast luminescence turn-off method to determine the concentration of MTX. To find the most sensitive QDs architecture to the presence of MTX, two types of nanoparticles were examined as detector systems: (i) a series of size-selected fractions of non-cadmium AgInS/ZnS QDs and (ii) alloyed CdZnSeS and CdZnSeS/ZnS QDs. All tested QDs in aqueous colloids were coated with thioglycolic acid as a surface stabilizing ligand. An examination of luminescence intensity and lifetime decreasing in the presence of MTX allowed us to evaluate the effect of the structure and composition of QDs on the efficiency of luminescence quenching by MTX. A detailed study demonstrates a predominantly static quenching mechanism, via the formation of complexes with high binding constants (∼106-107 M−1). The wide variability in the composition and size of QDs made it possible to achieve a low MTX detection limits (3 and 5 nM for the third fraction of AgInS/ZnS and CdZnSeS/ZnS QDs, respectively). Thus, the use of luminescent QDs as a direct detection system is promising for monitoring MTX concentrations

Construction of 1,3,5-Triazine-Based Prisms and Their Enhanced Solid-State Emissions.

In this study, two trigonal prisms based on the 1,3,5-triazine motif (SA and SB), distinguished by hydrophobic groups, were prepared by the self-assembly of tritopic terpyridine ligands and Zn(II) ions. SA and SB exhibited high luminescence efficiencies in the solid state, overcoming the fluorescence quenching of the 1,3,5-triazine group caused by π-π interactions. Notably, SA and SB exhibited different luminescence behaviors in the solution state and aggregation state. SB with 12 alkyl chains exhibited extremely weak fluorescence in a dilute solution, but its fluorescence intensity and photoluminescence quantum yield (PLQY) were significantly enhanced in the aggregated state (with the increase in the water fraction), especially in the solid state. Different from the gradually enhanced efficiency of SB, the PLQY of SA gradually decreased with the increase in aggregation but still maintained a high luminescence efficiency. These two complexes exhibited different modes to solve the fluorescence quenching of 1,3,5-triazine in the solid state. The hierarchical self-assembly of SB exhibited nanorods owing to the hydrophobic interactions of alky chains, while SA aggregated into spheres under the influence of π-π interactions.

Luminescence Characteristics of Green Grossular Garnets

Some light green grossular garnets exhibit orange-red luminescence under long-wave and short-wave ultraviolet light. To characterize their luminescence behavior, we studied seven grossular garnets with typical colors ranging from light yellowish-green to intense green by using photoluminescence (PL), ultraviolet–visible (UV–Vis) spectroscopy, electron paramagnetic resonance (EPR), Electron Probe Microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). In the PL spectra of these grossular garnets samples, a broad band exists at about 589 nm and three sharp peaks appear at 697, 702 and 716 nm. The three-dimensional fluorescence spectra reveal two luminescence emissions. They are (1) a broad band near 600 nm; and (2) a series of sharp peaks centered at 697, 702 and 716 nm. In the UV–Vis spectra, two prominent asymmetrical absorption bands near 430 and 605 nm are related to Cr3+ or Cr3+/V3+, and minor absorption peaks at 408 and 419/420 nm are related to Mn2+. EMPA and LA-ICP-MS analysis confirmed the existence of trace elements Ti, V, Cr and Mn. Furthermore, the EPR spectrum excluded the existence of V2+ and V4+ and confirmed the existence of Mn2+, Cr3+ and Fe3+. Regarding V, an interesting phenomenon was reported in which the intensity of luminescence could be suppressed in grossular garnets with higher concentrations of V. These results imply that chromium and manganese are the luminescence activators in grossular garnets, and vanadium is a powerful quencher.

Luminescence and structural properties of europium doped titania in the 600–750 °C range

In this study, europium doped titania nanophosphors are synthetized and characterize in order to understand the relationship between structural changes induced by heat treatments and luminescence properties. After heat treatments, phase changes are observed between 600 °C and 700 °C and characterized using X-ray diffraction and Raman spectroscopy. These phase changes include the anatase – rutile transition and the apparition of secondary phases such as europium oxide and pyrochlore phase (Eu2Ti2O7). Along with the phase changes and crystallite size evolution, the luminescence intensity of the 5D0→ 7F2 transition and the lifetime decay are measured after green laser excitation (532 nm). The europium concentration is a key parameter to obtain a monotone and bijective relationship between the temperature and the luminescence behavior.

A New Look at the Explanation of Differences in Properties between La3+ and Lu3+ Titanate Hosts Occupied by Eu3+

In order to improve the quality of WLEDs, considerable efforts have been devoted to investigate red phosphor. In this study, two double perovskites La2MgTiO6 and La2ZnTiO6 and two novel pyrochlores Lu2MgTiO6 and Lu2ZnTiO6 doped with 1%Eu3+ were synthesized by the co-precipitation method. The crystal structure, absorption, excitation, and emission spectra of all samples were investigated in detail. Dissimilar luminescent behaviors of the studied samples were observed. Due to the different site symmetry of Eu3+, each compound exhibits a different emission spectrum. The emission of the magnetic dipole transition is dominant in all the spectra of the Lu-based hosts, while the forced electric dipole transition is the strongest one in the spectra of the others. Besides, the ones crystallized in double perovskite structures possess larger bandgaps and show a more intense emission from the 5D1 level of Eu3+ as compared to the pyrochlore compounds. Furthermore, the distinct mechanism of the cross-relaxation of four titanate compounds was investigated. The above findings contribute to the understanding of the two novel pyrochlore hosts.

Aggregation Induced Transition by Modulation of Substituent Groups on Rofecoxib Analogues and Multi‐Stimulus Response Properties

AbstractAggregation‐induced emission luminogens (AIEgens) have been widely investigated due to their promising applications in data storage, organic light‐emitting diodes, and deep tissue bioimaging as compared to conventional fluorophores. In this work, we have designed and synthesized two novel rofecoxib analogues functionalized with different terminal groups (−NH2, −Br) on the benzene ring B. Interestingly, the compound 2 a‐3 with −NH2 substituent shows aggregation‐caused quenching effect whereas the compound 1 b‐3 with −Br group displays aggregation‐induced emission (AIE) property which may be caused by the twisted conformation and restricted – stacking of 1 b‐3 according to the X‐ray single crystal diffraction analysis. These opposite results indicated that the terminal groups could have great influence on the photophysical properties of targets. Moreover, the compound 1 b‐3 exhibited multi‐stimuli response luminescence behaviors under various external stimuli including solvatochromism, mechanochromism and acidochromism. Furthermore, lipid droplets imaging investigation proved the compound 1 b‐3 was capable of achieving specific lipid droplets bioimaging. This work not only presents a better understanding of the structure‐fluorescent property relationship based on the scaffold of rofecoxib, but also provides a new avenue for spectral modulation and the development of new MSR materials.

Assessing the improved luminescence of SrCe1-xSmxO3 perovskite by concentration controlled extra oxidizer substitution

Strontium cerate perovskite nano phosphors when doped with rare earth elements show improved functional properties such as electrical conductivity and photoluminescence. Electrical conductivity investigations on doped strontium cerates have been studied widely over decades for application in electrochemical cells, hydrogen sensors, hydrogen extractors, etc. But only minimal research has been developed in the amelioration of photoluminescence in rare earth-doped strontium cerates. In the present study, samarium-doped strontium cerate perovskite nanophosphors were considered for utilization in optoelectronic applications. The perovskites SrCe1-xSmxO3 (x = 0.01,0.02,0.03) were prepared via a low-temperature gel combustion approach with citric acid as chelating agent and ammonia solution as an extra oxidizer. The influence of concentration variation on the evolution behaviour of the crystalline phase as well as the luminescence characteristics of ceramic powders are investigated using X-ray diffraction and Photoluminescence characterization techniques. Experimental results indicate that the calcinating temperature of 1223 K in gel combustion synthesis, much lower than the conventional solid-state reaction is only needed for the single-phase perovskite formation. Also, a comparison study of the luminescence behaviour by replacing internal constituent extra oxidizer ammonia solution with ammonium nitrate is observed in this study, and conditions for maximum luminescence intensity are hence discussed. The observed results on photoluminescence studies indicate that an enhancement in the luminescence intensity of SrCe0.98Sm0.02O3 occurred when we replaced extra oxidizer ammonia solution with ammonium nitrate. Thus, a bright orange-scarlet red emitting perovskite nano phosphor SrCe0.98Sm0.02O3 by the later technique can be synthesized and can act as an inevitable red phosphor coating the chip in LEDs, which can be a great revolution in energy savings applications.

Investigation of structural modification, surface chemical states, and luminescence behavior of rapid thermal annealing treated MgTiO3 thin films

Investigation of structural modification, surface chemical states, and luminescence behavior of rapid thermal annealing treated MgTiO3 thin films

Effects of activator oxidation number and matrix composition on structure feature, microscopic morphology, and luminescence behavior of blue-emitting (Gd,Y)3Al5O12:Bi phosphors

Effects of activator oxidation number and matrix composition on structure feature, microscopic morphology, and luminescence behavior of blue-emitting (Gd,Y)3Al5O12:Bi phosphors

Construction of anisotropic near-infrared luminescent elastomers via magnetic orientation

We here report a Yb-containing Near-Infrared hybrid elastomer with anisotropic mechanical behavior as well as anisotropic luminescent performance, which is constructed by aligning the superparamagnetic nanoparticle coated alumina (Fe/Al2O3) platelets with a magnetic field, then the oriented structure is fixed by in situ evaporation. Because the mechanical reinforcement of aligned Fe/Al2O3 platelets to the polymeric elastomer is anisotropic, the mechanical strength parallel to the magnetic field is much higher than that of perpendicular to the magnetic field. Meanwhile, the hybrid elastomer also shows anisotropic NIR luminescence behavior, since the “shading effect” of the aligned Fe/Al2O3 platelets on the Yb3+ emitting centers is orientation-dependent. The method we report here may have great potentials in anisotropic sensing and physiological signal transduction, etc., which are essential for electronic skin and smart actuator.

Viscosity-Responsive Electrochemiluminescence of Diphenylbenzofulvene Derivatives.

The development of superior probes is highly desirable and valuable for viscosity measurement. Herein, we designed and reported a series of diphenylbenzofulvene (DPBF)-based organic luminophores according to the molecular regulation strategy. There are two free-rotating phenyl groups attached to the rigid fluorene skeleton in the DPBF, enabling its unique propeller-like noncoplanar chemical structure. Benefiting from this, DPBFs could feature outstanding PL and ECL emissions with intriguing aggregation-induced characteristics. Experimental and theoretical investigations revealed that substituent, spatial structure, and molecular orbital energy profoundly affected their luminescent behaviors. It was disclosed that fluoro-substituted DPBF(F)2 with a smaller LUMO-HOMO band gap demonstrated the strongest ECL emission and was selected as the optimal ECL emitter. Finally, DPBF(F)2 featured a linear response to the viscosity and VC content with lower limits of detection (LOD) of 5.69 μcP and 38.2 nM, respectively. This study represents the first example of the ECL probe toward viscosity and will be of great significance for both ECL application and viscosity measurement.

Polymorphous meso-Dicyanovinyl-Substituted Tetraphenylethylene Derivative Showing Distinguishing Two-Color Emission and Ultrahigh-Contrast Mechano-Responsive Luminescence Behavior

Polymorphous <i>meso</i>-Dicyanovinyl-Substituted Tetraphenylethylene Derivative Showing Distinguishing Two-Color Emission and Ultrahigh-Contrast Mechano-Responsive Luminescence Behavior

Stretchable and Self-Healing Elastomers with Aggregation-Induced Emission Based on Hydrogen Bonding Cross-Linked Networks

With the fast advancement of flexible and stretchable electronics, the development of organic semiconductors with intrinsic stretchability and self-healing properties is desirable and significant yet remains a substantial challenge. Herein, we propose a simple and effective synthetic strategy to construct intrinsically stretchable and self-healing organic light-emitting elastomers via incorporating aggregation-induced emission (AIE) luminogens into hydrogen-bonding cross-linked networks. Owing to the hydrogen-bonding interactions within the networks, the resulting light-emitting elastomers achieved a stress–strain of about 700% and a self-healing efficiency of over 70% under ambient conditions. More importantly, the resulting elastomers have been examined to be highly adhesive and compatible with the silver nanowire networks, exhibiting smart luminescence behaviors and excellent conductivity. This study sheds light on the design and development of stretchable and self-healing organic light-emitting elastomers with promising optoelectronic characteristics, which would inspire a wide range of fancy applications for flexible and stretchable electronics.

Solvatochromism as a Novel Tool to Enumerate the Optical and Luminescence Properties of Plastic Waste Derived Carbon Nanodots and Their Activated Counterparts.

Herein, we have developed a one-pot methodology to synthesise three types of C-dots and their activated counterparts from three different types of waste plastic precursors such as poly-bags, cups and bottles. The optical studies have shown the significant change in the absorption edge in case of C-dots in comparison to their activated counterparts. The respective variation in the sizes is correlated with the change in electronic band gap values of formed particles. The changes in the luminescence behaviour are also correlated with transitions from the edge of the core of formed particles. The obtained variations in the Stokes shift values of C-dots, and their ACs were used to explore the types of surface states and their related transitions in particles. The mode of interaction between C-dots and their ACs was also determined using solvent-dependent fluorescence spectroscopy. This detailed investigation could provide significant insight on the emission behaviour and the potential usage of formed particles as an effective fluorescent probe in sensing applications.

BiOCl: Dy3+/Ba2+ nanophosphors: Synthesis, luminescence characteristics and applications in latent fingerprint detection and cheiloscopy

Here, we systematically investigate the structural and luminescent behaviour of Ba2+ co-doped BiOCl:Dy3+ nanophosphors synthesized by a cost-effective solid-state reaction method. The effect of Barium concentration on the structural and optical properties of Dy3+ doped BiOCl phosphors was examined in detail. The X-ray Diffraction (XRD) patterns and Rietveld refinement revealed that the as-prepared phosphors had a tetragonal crystal structure with the space group P4/nmm. X-ray Photon Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), and Raman analysis unveiled the elemental composition and vibrational modes of the prepared sample and it directly confirms the incorporation of Dy3+ and Ba2+ ions into the BiOCl lattice. The effect of Ba2+ co-doping on photoluminescence of optimized BiOCl:2%Dy3+ was studied and, observed a remarkable enhancement in the emission intensity. The decay time obtained in microseconds implied the fast-switching response of the nanophosphors. The prepared nanophosphors at optimum concentration were used for the development and visualization of latent fingerprints (LFPs) and Cheiloscopy for individual identification in forensic science. Our results reveal that the synthesized nanophosphors have potential applications in the field of color displays and may act as a valuable tool for law enforcement.

Boosting Red Luminescence of Mn4+ in Tantalum Heptafluoride Based on an Ab Initio-Facilitated Sensitizer and Hydrophobic Surface Modification

A narrow-band red-light component is critical to establish high color rendition and a wide color gamut of phosphor-converted white-light-emitting diodes (pc-WLEDs). In this sense, Mn4+-doped K2SiF6 fluoride is the most successful material that has been commercialized. As with K2SiF6:Mn4+ phosphors, Mn4+-doped tantalum heptafluoride (K2TaF7:Mn4+) fulfills a similar luminescence behavior and has been brought in a promising narrow-band red phosphor. But the limited brightness and low moisture-resistant performances have inevitably blocked its practical application. Herein, we employed the density functional theory (DFT)-based ab initio estimation approach to quickly identify the proper sensitizer by systematically investigating the electronic-band coupling between the several possible sensitizers (Rb, Hf, Zr, Sn, Nb, and Mo) and the luminescent center (Mn). Combined with experimental results, Mo was demonstrated to be the optimal sensitizer, which resulted in a 60% enhancement of the emission. On the side, the moisture sensitivity has been effectively improved via grafting the hydrophobic octadecyltrimethoxysilane (ODTMS) layer on the phosphor surface. Through employing the K2TaF7:Mn4+,Mo6+@ODTMS composite as a red component, warm WLEDs with good performance were achieved with a correlated color temperature (CCT) of 4352 K, a luminous efficacy (LE) of 90.1 lm/W, and a color rendering index (Ra) of 83.4. In addition, a wide color gamut reaching up to 102.8% of the NTSC 1953 value could be realized. Aging tests at 85 °C and 85% humidity for 120 h on this device manifested that the ODTMS-modified phosphor had much better moisture stability than that of the unmodified one. These studies provided viable tools for optimizing Mn4+ luminescence in fluoride hosts.

Distinct Luminescent Thermal Behaviors of Yb3+- and Nd3+-Sensitized Core/Shell Upconversion Nanocrystals

Luminescent materials generally exhibit the thermal quenching due to accelerated nonradiative transitions at elevated temperatures. Recently, the discovery of anomalous thermally induced luminescence enhancement in lanthanide-doped upconversion nanocrystals (UCNCs) has aroused wide attention. The research on this topic not only deepens the understanding on the upconversion luminescence (UCL) mechanism but also promotes frontier applications based on UCNCs. Herein, comparative studies on temperature-dependent UCL properties were performed between Yb3+- and Nd3+-sensitized active-core/active-shell UCNCs. Opposite luminescent thermal behaviors were revealed for these two types of core/shell NCs, and the underlying mechanisms were elucidated with the assistance of temperature-dependent steady/transient spectral analysis under various atmospheres. Yb3+-sensitized active-core/active-shell NCs exhibited an anomalous luminescence enhancement with increasing temperature, which was attributed to the thermally alleviated quenching of surface-adsorbed water molecules. By contrast, Nd3+-sensitized active-core/active-shell NCs showed a normal thermal quenching due to rapidly increased deactivation rates of Nd3+ ions at elevated temperatures, although their UCL intensity was also affected by the quenching effect of surface-adsorbed water molecules. Highly secure anti-counterfeiting patterns were also demonstrated using the nanohybrids of Yb3+- and Nd3+-sensitized core/shell UCNCs as luminescent inks on the basis of their opposite luminescent thermal behaviors. This work provides new insights into luminescent thermal behaviors and energy loss pathways of lanthanide-doped UCNCs.

Solubility tuning of alkyl amine functionalized carbon quantum dots for selective detection of nitroexplosive

The major issue of luminescent carbon quantum dots (CQDs) is the solubility in wide range of solvent and disappearance of luminescence behavior in its solid state due to aggregation caused quenching. To resolve this issue, in the present work, we have tuned the solubility of carbon quantum dots in different kinds of solvents through surface functionalization technique. Here, we have synthesized three sets of alkyl amine functionalized carbon quantum dots from citric acid and alkyl amine by solvothermal method. We have observed that the solubility of CQDs increases from aqueous medium to organic medium with increasing length of hydrophobic alkyl chains attached at the surface of CQDs. It is seen that n-butyl amine functionalized CQDs (C4-CQD) are soluble in any type of solvents. Here we have also observed that the C4-CQD shows aggregation induced emission instead of aggregation caused quenching in solid state and shows bright yellow luminescence color upon excitation. Besides this, we also report selective detection of both dinitroaniline (DNA) and dinitrophenol (DNP) using this C4-CQD via fluorescence quenching and colorimetric methods. In organic medium both shows significant quenching with emission peak of carbon quantum dots is red shifted (∼30 nm) in presence of DNP whereas no significant peak shift is observed for DNA. CQDs containing paper strip shows yellow spot in presence of DNP but no such characteristic color is appeared after addition of DNA. Using these two techniques, we have selectively identified both DNA and DNP among other nitro compounds by our as-synthesized carbon dots.