Remarkable Luminescence Properties Research Articles

Room Temperature Phase Transition and Luminescence Behavior of a Novel Metal‐Free Ionic Crystal [C7H16NO][ClO4

AbstractMetal‐free ionic crystals have attracted tremendous attention for their environmental friendliness, biocompatibility, easy fabrication and structural variability. Herein, a metal‐free ionic crystal [C7H16NO][ClO4] ([C7H16NO]=1‐methyl‐4‐piperidinemethanol) with a dielectric transition at room temperature was designed and constructed. Differential scanning calorimetry (DSC) proved that there exists a reversible phase transition near room temperature at 304 K, accompanied with switchable dielectric behaviors between the low and high dielectric states. The single crystal structure show that the mechanism of such structural phase transition mainly results from the dynamic motion of perchlorate anions. The compound is further shown to exhibit remarkable luminescent properties, characterized by a prolonged lifetime of 18.6 ns. This work offers valuable insights into the construction of room temperature phase‐transition ionic crystals involved with dielectric switching and blue luminescence properties.

Temperature‐Dependent Reversible Afterglow Between Green, Orange, and Red in Dual‐Delay Organic Doped Material

AbstractAchieving a wide‐range color‐tunable and dynamically long‐afterglow emission in a single‐doped system remains a challenge. In this study, a unique host‐guest doped material, TPA‐PTPQ/TPA, exhibits dual‐delay emission at 516 and 605 nm, both with long lifetimes of up to 108 and 145 ms, which derives from thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) mechanisms, respectively. Notably, this host‐guest material demonstrates a temperature‐dependent dynamically reversible afterglow characteristic, transitioning green, orange, and red with a substantial spectra shift of ≈90 nm under different temperature conditions. This phenomenon is due to the diverse temperature effect on TADF and RTP emissions. These remarkable luminescence properties are successfully applied in security checks and anti‐counterfeiting encryption. This study provides valuable insights into the design of dynamically reversible dual‐delay‐emissive long‐afterglow luminescent materials based on a host‐guest doping system.

Nitrogen-Doped Carbon Dots: A New Powerful Fluorescent Dye with Substantial Effect on Bacterial Cell Labeling.

Carbon dots (CDs)-minute carbon nanoparticles with remarkable luminescent properties, photostability, and low toxicity-show potential for various applications. CDs synthesized using citric acid and urea are the least toxic to biological environments. Here, we aimed to explore the effect of CDs synthesized using citric acid and urea at 50, 33, and 25% (CDs 1/1, 1/2, and 1/3, respectively) weight ratios in a microwave on bacterial cell fluorescence sensing and labeling. The nanoscale properties of CDs were investigated via transmission electron microscopy and dynamic light scattering particle size analysis. X-ray powder diffraction confirmed the graphitic structures of CDs. X-ray photoelectron spectroscopy revealed that the nitrogen content increased gradually with increasing urea ratios, indicating functional group changes. Transient photoluminescence decay periods demonstrated superior fluorescence intensity of CDs 1/3 under blue, green, and red lights. The use of CDs was notably more efficient than traditional methods in staining bacterial cells. Fluorescence microscopy of 10 g-positive and 10 g-negative bacteria revealed enhanced staining of Gram-positive strains, with CDs 1/3 presenting the best results. The CDs exhibited excellent photostability, maintaining poststaining fluorescence for 100 min, surpassing the performance of conventional dyes. CDs could serve as potential fluorescent dyes for the rapid discrimination of Gram-positive and Gram-negative bacteria.

Ligand-Induced Red-Emitting Copper Nanoclusters for Selective Fluorescence Determination of Aluminum Ions.

Monitoring levels of excessive aluminum ions (Al3+) is crucial as it can harm the immune system, reduce enzyme activity, cause cell death, and damage environmental and biological systems. Developing a fast and efficient Al3+ ion determination method is the key to addressing this issue. In this work, red-emitting fluorescent copper nanoclusters (CuNCs) were synthesized using N-acetyl-l-cysteine (NAC) as a ligand and CuCl2·2H2O through a facile procedure. The NAC-CuNCs exhibited a large Stokes shift and displayed remarkable luminescence properties. A method for detecting Al3+ through a fluorescence probe was proposed. Its fluorescence mechanism was also explored. The probe showed rapid responsiveness (within 1 min) to Al3+ ion determination. The detection limit for Al3+ was found to be 19.7 nM, which is significantly lower than the WHO's value and most reports, with a linear range of 0-52.9 μM. The determination of Al3+ concentrations in actual water using the fluorescence probe yielded satisfactory outcomes. Moreover, the visual detection of Al3+ ions was also achieved through a smartphone, which can enhance its fast and practical detection.

Blue Phosphorescent Pt(II) Compound Based on Tetradentate Carbazole/2,3'-Bipyridine Ligand and Its Application in Organic Light-Emitting Diodes.

The tetradentate ligand, merging a carbazole unit with high triplet energy and dimethoxy bipyridine, renowned for its exceptional quantum efficiency in coordination with metals like Pt, is expected to demonstrate remarkable luminescent properties. However, instances of tetradentate ligands such as bipyridine-based pyridylcarbazole derivatives remain exceptionally scarce in the current literature. In this study, we developed a tetradentate ligand based on carbazole and 2,3'-bipyridine and successfully complexed it with Pt(II) ions. This novel compound (1) serves as a sky-blue phosphorescent material for use in light-emitting diodes. Based on single-crystal X-ray analysis, compound 1 has a distorted square-planar geometry with a 5/6/6 backbone around the Pt(II) core. Bright sky-blue emissions were observed at 488 and 516 nm with photoluminescent quantum yields of 34% and a luminescent lifetime of 2.6 μs. TD-DFT calculations for 1 revealed that the electronic transition was mostly attributed to the ligand-centered (LC) charge transfer transition with a small contribution from the metal-to-ligand charge transfer transition (MLCT, ~14%). A phosphorescent organic light-emitting device was successfully fabricated using this material as a dopant, along with 3'-di(9H-carbazol-9-yl)-1,1'-biphenyl (mCBP) and 9-(3'-carbazol-9-yl-5-cyano-biphenyl-3-yl)-9H-carbazole-3-carbonitrile (CNmCBPCN) as mixed hosts. A maximum quantum efficiency of 5.2% and a current efficiency of 15.5 cd/A were obtained at a doping level of 5%.

A postsynthetically modified MOF-808 as a fluorescent sensor for the detection of nitrofurazone antibiotic

The excessive use of nitrofuran drugs in human healthcare as well as in animal husbandry are a major threat to both the environment and human health. As a result, there is an urgent requirement for extensive research to develop materials that can efficiently detect these residual pollutants. However, developing sensor materials with high sensitivity, selectivity, and recyclability is still a challenging task. Herein, we design and synthesize a stable photoluminescent metal–organic framework (MOFs) named MOF-808-AAA, where we have first time integrated a fluorescent organic molecule, 3-anthracen-9-yl-acrylic acid (AAA), via solvent-assisted ligand exchange (SALE) method. Comprehensive structural characterization employing various techniques including PXRD, FT-IR spectra, N2 adsorption, 1H NMR, UV–Vis, and fluorescence spectra, confirmed the successful integration of AAA into the MOF-808 framework. The synthesized MOF-808-AAA demonstrates remarkable luminescence properties and exhibits quick sensitivity towards nitrofurazone (NFZ) with quenching constant (Ksv) of 2.98 × 104 M−1 and low detection limit of 0.51 µM in acetonitrile medium, demonstrating the efficacy of MOF-808-AAA as a promising fluorescent chemical sensor for NFZ detection. In addition, we have proposed a plausible turn off sensing mechanism based on photophysical and electrochemical studies.

Near-Unity Green Luminescent Hybrid Manganese Halides as X-ray Scintillators.

The increasing demands in optoelectronic applications have driven the advancement of organic-inorganic hybrid metal halides (OIMHs), owing to their exceptional optical and scintillation properties. Among them, zero-dimensional (0D) low-toxic manganese-based scintillators have garnered significant interest due to their exceptional optical transparency and elevated photoluminescence quantum yields (PLQYs), making them promising for colorful light-emitting diodes and X-ray imaging applications. In this study, two OIMH single crystals of (Br-PrTPP)2MnBr4 (Br-PrTPP = (3-bromopropyl) triphenylphosphonium) and (Br-BuTPP)2MnBr4 (Br-BuTPP = (4-bromobutyl) triphenylphosphonium) were prepared via a facile saturated crystallization method. Benefiting from the tetrahedrally coordinated [MnBr4]2- polyhedron, both of them exhibited strong green emissions peaked at 517 nm owing to the d-d electron transition of Mn2+ with near-unity PLQYs of 99.33 and 86.85%, respectively. Moreover, benefiting from the high optical transparencies and remarkable luminescence properties, these manganese halides also exhibit excellent radioluminescent performance with the highest light yield of up to 68,000 photons MeV-1, negligible afterglow (0.4 ms), and linear response to X-ray dose rate with the lowest detection limit of 45 nGyair s-1. In X-ray imaging, the flexible film made by the composite of (Br-PrTPP)2MnBr4 and PDMS shows an ultrahigh spatial resolution of 12.78 lp mm-1, which provides a potential visualization tool for X-ray radiography.

Photo-induced luminescence mechanism and the correlated defects characteristics in the sol-gel derived samarium ion substituted tin oxide (Sn1-xSmxO2) nanoparticles

Rare earth complexes have gained attention in recent years for their remarkable luminescence properties, especially their long lifetimes, clear emission bands, and significant luminous quantum efficiency. In the ultraviolet area, the lanthanide ions exhibit relatively tiny absorption. The current investigation systematically portrays the tailoring of the micro-structural, opto-electonic and defect related features of the sol-gel derived pristine and rare earth element-samarium (Sm3+) substituted tin oxide (SnO2) i.e., Sn1-xSmxO2 (x = 0.0, 0.1, 0.2 & 0.3) nanoparticles (NPs). The structural, optical, electronic, morphological, photo-induced luminescence and defects related characteristics of the NPs were explored as a function of samarium (Sm3+) substitution level. In-depth analysis of the structure-property correlation of the Sn1-xSmxO2 NPs is the goal of this study, focusing especially on the properties related to vacancy evolution and luminescence. The elemental mapping results revealed through energy dispersive X-ray spectroscopic (EDS) technique confirmed that the Sm-substitution is distributed uniformly throughout the NPs. The X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) studies corroborate that the Sm3+ substitution in the SnO2 matrix causes the decrease in crystallite size of the NPs and increase in the dislocation density. A monotonic increase in lattice strain has been observed using the Williamson – Hall (W – H) approach, which is in line with the NPs' increased dislocation density and decreased crystallite size with the Sm3+ substitution level. The presence of vacancy-type defects inside the NPs was demonstrated by positron annihilation lifetime (PAL) spectroscopic measurements, and a decrease in defects was noticed as the level of Sm3+ substitution increased. To explore the optical characteristics and the evolution of the energy band gap with Sm3+ substitution level, the optical absorption (OA) spectroscopic measurement was carried out. As the Sm-substitution level rises, the optical energy band gap of the substituted SnO2 NPs widens relative to that of pure SnO2 NPs. The existence of various absorbance bands corresponding to the atomic vibrations within the NPs were investigated by the Fourier-transform infrared (FT-IR) spectroscopic technique. The photo-induced fluorescence (FL) emission spectroscopic analysis evidenced that the defect density decreased as the Sm-substitution level increased, which is in accordance with the PAL spectroscopic studies. The FL spectra showed the two typical near band edge (NBE) and deep level emission (DLE) peaks of the NPs. The proportion of different defects and vacancies associated with the FL emission transitions are portrayed as Pie-chart diagrams. The tailored NPs can establish to be effective candidates for possible spintronic and optoelectronic applications including magneto-optical devices.

Synthesis and Optical Properties of Anion‐Responsive X‐shaped π‐Electronic System

AbstractThe properties of donor‐π‐acceptor molecules are strongly influenced by the electron density and configuration of both donor and acceptor moieties. In particular, X‐shaped molecules, where two linear π‐conjugation systems ended by donors and/or acceptors are crossed in their middle, are well‐known to separate frontier molecular orbitals, and the donor and acceptor strongly influence the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), respectively. A novel X‐shaped molecule, containing a diphenylamino group as the donor and a dimesitylboryl group as the acceptor, was synthesized to modulate the optical properties via anion complex formation. The X‐shaped molecule formed [1+1]‐ and [1+2]‐type anion complexes in solution, and a negative cooperative effect for the formation of the [1+2]‐type anion complex was observed. UV‐vis and fluorescence spectroscopy reveled the changes in the optical properties by the formation of anion complexes, with the spectral changes upon anion addition were consistent with the theoretical spectra obtained from time‐dependent density functional theory calculations. Furthermore, the X‐shaped molecule, which exhibits remarkable luminescence properties even in the solid state, demonstrated electroluminescent behavior.

Ultrasound-assisted nucleation and growth of hydroxyl-protected and ligand-free Cs3Cu2X5 nanocrystals with bright luminescence.

The commercial applications of lead halide perovskites are hindered by their negative environmental impact and inherent instability. Consequently, developing environmentally friendly copper-based perovskite materials is crucial for future solid-state lighting and display applications. In this study, an ultrafast high-power ultrasonic synthesis strategy was utilized to achieve uniform nucleation and growth of Cs3Cu2X5 (X = Cl, Br, I) nanocrystals (NCs) that possess remarkable luminescence properties, hydroxyl protection, and ligand-free characteristics. These Cs3Cu2X5 NCs exhibited a tunable spectral range spanning from 446 to 525 nm, accompanied by photoluminescence quantum yields (PLQYs) varying from 0.2% to 79.2%. The spectral attributes of the NCs were effectively controlled by modulating the halide type and composition. It is worth noting that density functional theory (DFT) calculations offer valuable insights into the synthesis of NCs and the selection of suitable alcohol solvents. Moreover, we successfully fabricated an efficient and stable white light-emitting diode (WLED) with a high luminous efficiency of 23 lm W-1 and CIE color coordinates of (0.3266, 0.3487). Our work provides a new strategy to synthesize Cs3Cu2X5 NCs and holds promise for their potential application in display and lighting devices.

Thiele's Fluorocarbons: Stable Diradicaloids with Efficient Visible-to-Near-Infrared Fluorescence from a Zwitterionic Excited State.

Thiele's hydrocarbon was the first synthesized diradicaloid in the search for stable open-shell structures, but it remains sensitive to oxygen and light. We here report the synthesis of Thiele's fluorocarbon (TFC) and its derivatives exhibiting exceptional thermal, oxidative, and photostability. TFCs have remarkable luminescent properties with yellow to NIR fluorescence and up to 100% quantum yields. X-ray crystallography and ESR spectroscopy confirm their closed-shell quinoidal ground state. As expected from their symmetric nonpolar structure, the TFCs' absorption spectra show no solvent effect, but their emission reveals an extraordinarily large Stokes shift which increases with solvent polarity (from 0.9 eV in cyclohexane to 1.5 eV in acetonitrile). We show that this behavior is a result of sudden polarization, leading to a zwitterionic excited state.

Pyrene-Fused Poly-Aromatic Regioisomers: Synthesis, Columnar Mesomorphism, and Optical Properties.

π-Extended pyrene compounds possess remarkable luminescent and semiconducting properties and are being intensively investigated as electroluminescent materials for potential uses in organic light-emitting diodes, transistors, and solar cells. Here, the synthesis of two sets of pyrene-containing π-conjugated polyaromatic regioisomers, namely 2,3,10,11,14,15,20,21-octaalkyloxypentabenzo[a,c,m,o,rst]pentaphene (BBPn) and 2,3,6,7,13,14,17,18-octaalkyloxydibenzo[j,tuv]phenanthro [9,10-b]picene (DBPn), is reported. They were obtained using the Suzuki-Miyaura cross-coupling in tandem with Scholl oxidative cyclodehydrogenation reactions from the easily accessible precursors 1,8- and 1,6-dibromopyrene, respectively. Both sets of compounds, equipped with eight peripheral aliphatic chains, self-assemble into a single hexagonal columnar mesophase, with one short-chain BBPn homolog also exhibiting another columnar mesophase at a lower temperature, with a rectangular symmetry; BBPn isomers also possess wider mesophase ranges and higher mesophases' stability than their DBPn homologs. These polycyclic aromatic hydrocarbons all show a strong tendency of face-on orientation on the substrate and could be controlled to edge-on alignment through mechanical shearing of interest for their implementation in photoelectronic devices. In addition, both series BBPn and DBPn display green-yellow luminescence, with high fluorescence quantum yields, around 30%. In particular, BBPn exhibit a blue shift phenomenon in both absorption and emission with respect to their DBPn isomers. DFT results were in good agreement with the optical properties and with the stability ranges of the mesophases by confirming the higher divergence from the flatness of DBPn compared with BBPn. Based on these interesting properties, these isomers could be potentially applied not only in the field of fluorescent dyes but also in the field of organic photoelectric semiconductor materials as electron transport materials.

Using a diphenyl-bi-(1,2,4-triazole) tricarbonylrhenium(I) complex with intramolecular π-π stacking interaction for efficient solid-state luminescence enhancement.

Since intramolecular π-π stacking interactions can modify the geometry, crystal packing mode, or even the electronic properties of transition metal complexes, they are also likely to influence the solid-state luminescence properties. Following this concept, a new tricarbonylrhenium(I) complex (Re-BPTA) was designed, based on a simple symmetrical 5,5'-dimethyl-4,4'-diphenyl-3,3'-bi-(1,2,4-triazole) organic ligand. The complex was prepared in good yield using a three-step procedure. The crystallographic study revealed that both phenyl rings are located on the same side of the molecule, and twisted by 71° and 62°, respectively, with respect to the bi-(1,2,4-triazole) unit. They overlap significantly, although they are slipped parallel to each other to minimize the intramolecular interaction energy. The π-π stacking interaction was also revealed by 1H NMR spectroscopy, in good agreement with the results of theoretical calculations. In organic solutions, a peculiar electrochemical signature was observed compared to closely-related pyridyl-triazole (pyta)-based complexes. With regard to the optical properties, the stiffness of the Re-BPTA complex led to the stabilization of the 3MLCT state, and thus to an enhancement of the red phosphorescence emission compared to the more flexible pyta complexes. However, an increased sensitivity to quenching by oxygen appeared. In the microcrystalline phase, the Re-BPTA complex showed strong photoluminescence (PL) emission in the green-yellow wavelength range (λPL = 548 nm, ΦPL = 0.52, 〈τPL〉 = 713 ns), and thus a dramatic solid-state luminescence enhancement (SLE) effect. These attractive emission properties can be attributed to the fact that the molecule undergoes little distortion between the ground state and the triplet excited state, as well as to a favorable intermolecular arrangement that minimizes detrimental interactions in the crystal lattice. The aggregation-induced phosphorescence emission (AIPE) effect was clear, with a 7-fold increase in emission intensity at 546 nm, although the aggregates formed in aqueous medium were much less emissive than the native microcrystalline powder. In this work, the rigidity of the Re-BPTA complex is reinforced by the intramolecular π-π stacking interaction of the phenyl rings. This original concept provides a rhenium tricarbonyl compound with very good SLE properties, and could be used more widely to successfully develop this area of research.

Pseudo-Tetrahedral Copper(I) Symmetrical Formamidine Dithiocarbamate-Phosphine Complexes: Antibacterial, Antioxidant and Pharmacokinetics Studies

Three copper(I) dithiocarbamate–phosphine complexes of the general formula Cu(PPh3)2L were synthesized by metathesis reactions of the potassium salt of the dithiocarbamate ligand L and the precursor complex Cu(PPh3)2NO3 in an equimolar ratio. L represents N,N′-bis(2,6-dimethylphenyl)formamidine dithiocarbamate L1 in complex 1, N,N′-bis(2,6-disopropylphenyl) formamidine dithiocarbamate L2 in complex 2, and N,N′-dimesitylformamidine dithiocarbamate L3 in complex 3. The single-crystal X-ray structure revealed the coordination of the copper atom to two sulfur atoms of the dithiocarbamates, as well as two phosphorus atoms of the PPh3 units, which resulted in distorted tetrahedral geometries. The calculated τ4 (tau factor) values for 1, 2 and 3 were 0.82, 0.81 and 0.85, respectively, confirming the pseudo-tetrahedral geometry proposed. Complexes 1–3 showed remarkable luminescent properties in CH2Cl2 at room temperature. All three complexes showed moderate-to-low antibacterial potential against Gram-negative bacteria, while none of the complexes were active against Gram-positive bacteria. The DPPH assay studies showed that complex 2 had the lowest IC50 (4.99 × 10−3 mM),and had higher DPPH free radical scavenging ability than 1 and 3. The pharmacological estimations of 1–3 showed that all of the complexes showed minimal violation of Lipinski’s rule.

Optical Properties of Transparent Rare-Earth Doped Sol-Gel Derived Nano-Glass Ceramics.

Rare-earth doped oxyfluoride glass ceramics represent a new generation of tailorable optical materials with high potential for optical-related applications such as optical amplifiers, optical waveguides, and white LEDs. Their key features are related to the high transparency and remarkable luminescence properties, while keeping the thermal and chemical advantages of oxide glasses. Sol-gel chemistry offers a flexible synthesis approach with several advantages, such as lower processing temperature, the ability to control the purity and homogeneity of the final materials on a molecular level, and the large compositional flexibility. The review will be focused on optical properties of sol-gel derived nano-glass ceramics related to the RE-doped luminescent nanocrystals (fluorides, chlorides, oxychlorides, etc.) such as photoluminescence, up-conversion luminescence, thermoluminescence and how these properties are influenced by their specific processing, mostly focusing on the findings from our group and similar ones in the literature, along with a discussion of perspectives, potential challenges, and future development directions.

2,7-Carbazole Derived Organoboron Compounds: Synthesis and Molecular Fluorescence.

Triarylboranes have drawn much attention in OLEDs owing to their remarkable solid-state luminescence properties. Here two new A-D-A type compounds, 2,7-bis(dimesitylboryl)-N-ethyl-carbazole (BCz) using triarylborane as electron acceptor and carbazole as electron donor while 2,7-bis((4-(dimesitylboryl)phenyl)ethynyl)-9-ethyl-carbazole (BPACz) using phenylacetylene as extra conjugated bridge, have been synthesized and their photoluminescence related properties in various states have been investigated both experimentally and theoretically. Both compounds show blue emission with high quantum yields, being potential candidates for blue OLED materials.

Cover Feature: Mechanochromic Luminescence (MCL) of Purely Organic Two‐Component Dyes: Wide‐Range MCL over 300 nm and Two‐Step MCL by Charge‐Transfer Complexation (Chem. Eur. J. 56/2021)

The creation of two-component dyes has proven to be an effective strategy to achieve remarkable mechanochromic luminescence (MCL) properties. The shift of the maximum emission wavelength (Δλem) range of a bis(1-pyrenylmethyl)diamine derivative has been significantly improved by mixing it with typical organic dyes that do not exhibit MCL behavior. Most notably, a wide-range MCL (Δλem=340 nm) has been achieved for a mixture with 3,4,9,10-perylenetetracarboxylic diimide. Furthermore, a two-step MCL has been realized by mixing with 9,10-anthraquinone. More information can be found in the Full Paper by S. Ito, T. Tachikawa, et al. (DOI: 10.1002/chem.202102700).

Eu3+-β-diketone functionalized covalent organic framework hybrid material as a sensitive and rapid response fluorescent sensor for glutaraldehyde

A covalent organic framework (named as TpDq) linked by β-ketoamine was prepared by imine condensation reaction with 1,3,5-triformylphloroglucinol (TFP) and 2,6-diaminoanthraquinone (DAAQ) as building blocks. Via employing a functionalized modification strategy, a new lanthanide complex Eu3+-β-diketone functionalized covalent organic framework hybrid material, Eu-TTA@TpDq (TTA = 2-thenoyltrifluoroacetone), has been synthesized. After post-synthetic modification (PSM), the shape and structure of the parent framework is well preserved and the modified material shows remarkable luminescence properties. Based on this, we designed it as a fluorescent probe and tried to use it to sense common aldehydes. The results indicate that Eu-TTA@TpDq exhibits a turn-off response toward glutaraldehyde which can distinguish from other common aldehydes. The fluorescent probe has the advantages of reusability, pH stability (4.50–8.52), fast luminescence response (<1 min) and low detection limit. The linear range of this method was 0–100 μM; the detection limit was 4.55 μM; the relative standard deviation was 2.16%. Furthermore, it has broad application prospect in both practical sensing of glutaraldehyde in water environment and simple detection of glutaraldehyde vapor. In addition, we preliminarily discussed the possible sensing mechanism.

Temperature sensitive properties and preparation of europium complexes with double ligands

Temperature sensitive paints (TSPs) are a class of rising materials for non-contact temperature measurement technology. Efficient complexes with remarkable luminescent properties play the core role in TSPs. Rare earth organic complexes are often used as probe molecules for TSPs because of their long fluorescence lifetime, narrow fluorescence emission peaks, high fluorescence intensity, and large Stokes shift. Herein, two europium-based complexes, Eu(PCCA)3 phen and Eu (PMCA)3 phen, were synthesized under hydrothermal conditions, using europium(III) oxide (Eu2 O3 ), p-chlorocinnamic acid (PCCA), p-methoxy cinnamic acid (PMCA) and 1,10-phenanthroline (phen) as raw materials. Two temperature sensitive paints (Eu(PCCA)3 phen/PMMA and Eu(PMCA)3 phen/PMMA) were obtained by the polymerization of methyl methacrylate (MMA) with different europium complexes. The structure, morphology, luminescent properties of the europium complexes and temperature quenching properties of the TSPs were characterized by infrared (IR) spectroscopy, scanning electron microscopy (SEM), and fluorescence spectroscopy. The fluorescence results show that both of the two TSPs have good temperature quenching performance in the range 20-100°C with high sensitivity 50-60°C and 80-90°C, respectively. Furthermore, the highest sensitivity of Eu(PCCA)3 phen/PMMA is greater than that of Eu(PMCA)3 phen/PMMA. This work can provide a universal way for preparing efficient TSPs in practical applications.

A novel narrow band blue-emitting phosphor Rb2ZrSi3O9: Eu2+ with low thermal quenching and high quantum efficiency

Developing phosphors with narrow band emission and excellent performance is the main goal of current leading research. In this study, a novel narrow band blue-emitting phosphor Rb2ZrSi3O9: Eu2+ was prepared that can be fully excited by near ultraviolet (NUV) light, emits a bright blue light peak at 470 nm, and has a full width at half maximum (FWHM) of 60 nm. The synthesized Rb2ZrSi3O9: Eu2+ had excellent photoluminescence properties that were reflected in its good thermal stability (up to 82%) and high internal quantum efficiency (up to 75%). These remarkable luminescence properties were mainly ascribed to the highly symmetric and dense crystal structure composed of [Si3O9]6- ring pairs. Multiple emission centers in the Rb2ZrSi3O9: Eu2+ phosphor were confirmed through the photoluminescence (PL) spectra and time-resolved (PL) spectra. A bright warm WLED device with a low correlated color temperature (3386 K) and high color-rendering index (CRI~89.3) was produced by combining the blue phosphor with (Sr, Ba)2SiO4: Eu2+ and CaAlSiN3: Eu2+ and NUV (380 nm). The results indicate that Rb2ZrSi3O9: Eu2+ could be a promising phosphor for use in WLEDs.