Luminescence Properties Research Articles

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.

Structure and luminescent properties of Nd(III) and Tb(III) coordination polymers with 2,4,6-pyridinetricarboxylate

Structure and luminescent properties of Nd(III) and Tb(III) coordination polymers with 2,4,6-pyridinetricarboxylate

Synthesis, crystal structure, magnetic studies, DNA binding, molecular docking studies, cytotoxicity and luminescence properties of a new coordination polymer copper(II) complex with 4,4′-trimethylenedipyridine and 1,10-phenanthroline

In the present work, a novel coordination polymer {[Cu(phen)(Tmdipy)(NO3)H2O](NO3) 2.5(H2O)}n (phen = 1,10-phenanthroline, Tmdipy = 4,4′- Trimethylenedipyridine), has been prepared and structurally determined by elemental analysis, IR, EPR, UV–visible and single-crystal X-ray crystallography. The complex crystallized in triclinic space group P -1, and the copper(II) shows a distorted octahedral geometry, with Jahn-Teller distortion occurring in the (4 + 2) CuN4O2 coordination sphere. The crystal structure evidences that the CP1 is formed of dinuclear [Cu(phen)(Tmdipy)(NO3)(H2O)]2 units weakly connected by nitrate anions giving rise to 1D polymeric chain structure. EPR measurement confirms about the distorted octahedral geometry of the complex. By using UV–Vis absorption, fluorescence spectroscopy, and cyclic voltammetric techniques, the binding studies of copper(II) complex with calf thymus DNA (CT-DNA) were investigated. Additionally, the gel electrophoresis method was used to examine the cleavage of pBR322 DNA by copper(II) complex and exhibited potent cytotoxic effects against human cell line (HepG2). Finally, magnetic properties, molecular docking studies and photoluminescence characteristics have been evaluated.

Multifunctional Lanthanide Metal-Organic Frameworks Are Used for Fluorescence Sensing of Bi3+, HPO42-, Flu, and PNBA and Application.

Using a nitrogen-containing tricarboxylic acid ligand (imidazole-1-yl) benzene-2,4,6-tricarboxylic acid (H3ttc) and lanthanide metal elements (Dy, Eu, Nd, and Gd), four lanthanide metal organic frameworks (Ln-MOFs) with the same structure, namely, {[Dy2 (Httc)3]·1.5DMF}n(1), {[Eu2 (Httc)3]·1.5DMF}n(2), {[Nd2 (Httc)3]·1.5DMF}n(3), and {[Gd2 (Httc)3]·1.5DMF}n(4), were synthesized under solvothermal conditions. The characterization analysis showed that the four isomorphic Ln-MOFs were trigonal crystals of the R3̅c space group, with good phase purity and thermal stability. Fluorescence analysis showed that complex 1 can be an excellent fluorescence sensor for Bi3+, HPO42-, and fluridine (Flu), while complex 2 can be an excellent fluorescence sensor for p-nitrobenzoic acid (PNBA). And their sensing mechanisms were discussed in detail. The fluorescent test paper and fluorescent seal were prepared by using the excellent luminescence properties of 1 and 2, and the pesticide on the surface of cherry tomato was detected. The applicability of these MOFs as fluorescence sensors was proved. Therefore, Ln-MOFs are expected to have unpredictable application prospects in the field of environmental detection.

Impact of sample preparation temperature on Li and Ce co-doped MgB4O7 dosimetry performance: A plausible scenario for controlling defect clustering

MgB4O7 co-doped with Ce and Li has been recognized as a promising dosimetric material for spatially-resolved optically stimulated luminescence (OSL) measurements. Nevertheless, conflicting information exists in the literature regarding its dosimetric characteristics. These include discrepancies in fading, the proportion of shallow traps, the range of linear dose response, and a notable absence of direct sensitivity comparisons. These discrepancies are likely attributed to variations in the synthesis methods utilized to produce this material. As part of our research initiative aiming at elucidating the influence of synthesis on the luminescence properties, we are examining in this contribution a single parameter – specifically, the sample preparation temperature – and assessing its impact on the luminescence properties. For the first time, we identified a correlation between the width of the thermoluminescence (TL) glow curves, the TL, optically stimulated luminescence (OSL), and radioluminescence (RL) intensities, as well as the fading characteristics over time and annealing temperature. We show that annealing at higher temperature leads to narrowing of the main TL peak (c.a. 240 °C at 5 °C/s heating rate) compared with samples prepared at lower temperatures, which in turn leads to a decrease in the integrated TL intensity of that peak. Despite exhibiting lower intensity, samples prepared at temperatures above 800 °C show less than 10 % TL/OSL fading over 60 days. Our measurements suggest an involvement of clustered defects for the samples prepared at 600 °C, with a shift towards a scenario of delocalized transitions in samples prepared at higher temperatures.

Luminescence spectra and site-occupation of Eu3+ centres in lithium antimonate LiSbO3 lattice

It is a challenge to accurately determine the exact location of the rare earth ion (RE) in the lattice when there are significant differences in radius, electronegativity and valence between the lattice cation and the corresponding RE activator in a host material. This study presents the findings on the luminescence and site occupancy of Eu3+ emission centers in the lithium antimonate LiSbO3 lattice. The phase-formation, structures, elemental composition, band transition characteristics, luminescence properties, and lifetimes of the Eu3+-doped phosphors were investigated. Eu3+-doped LiSbO3 exhibits a typical 5D0→7F2 red luminescence transition at 613 nm. Site-selective excitation, luminescence, and decay properties at the 7F0→5D0 transition wavelength were measured using a tunable pulsed narrow-band dye laser. Two Eu3+ luminescence centers in LiSbO3 were identified across the temperature range from 10 K to 300 K. The doping of RE(Eu3+) in LiSbO3 consistently occupies two crystallographic positions of Li+ and Sb5+. Furthermore, the probability of RE(Eu3+) ions preferentially occupying the Li+ (M) sites is notably high. The decay curves and luminescence lifetimes of the two Eu3+ centers were determined. Drawing from the experimental data, we discuss the potential defects induced by Eu3+ doping in LiSbO3 and the mechanism of charge compensation. These results could be instrumental in the advancement of new RE-activated luminescent materials or serve as a reference for investigating the specific positioning of RE ions within a phosphor lattice.

Multi-stimuli-responsive conductive and luminescent hydrogels for wearable sensors and information encryption transmission

Flexible electronic sensors with optical functions have promising applications in wearable sensing, information storage, encryption and transmission, but realizing multifunctional applications in a single system is still challenging. Herein, the conductive and luminescent hydrogel in a single system was fabricated by non-covalent crosslinked poly(vinyl alcohol) (PVA) network and covalent crosslinked acrylamide (AAm) and [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA) network, as well as doping Eu(PDA)3 and glycerol (GL). The acquired PVA0.9/P(AAm-co-SBMA0.5)/Eu(PDA)3/GL (P0.9P0.5EG) hydrogel possesses excellent mechanical properties, adhesion, self-healing capability, water retention ability, anti-freezing property, conductivity, self-powered property, and luminescent properties. Importantly, the hydrogel as a flexible sensor has excellent tensile strain sensitivity (GF = 17.8), pressure sensitivity (S = 1.191 kPa−1), quick response, and stable electrical signals output, which can be used for monitoring multiple movements as well as for information transmission with the help of Morse code. Moreover, the unique luminescent properties and multi-stimuli-responsive behavior also make the hydrogel monitor strain variations via detecting the luminescence signal changes. Notably, the particular process of information encryption transmission was further achieved by converting the luminescence signals to electrical signals. This work provides an alternative strategy for designing and preparing hydrogel sensors for multifunctional applications.

Solution processed high aspect ratio ultra-long vertically well-aligned ZnO nano scintillators for potential X-ray imaging applications

We report the photon (PL), electron (CL) and X-ray (XEL) induced luminescence characteristics of high aspect ratio ultra-long (~ 50 µm) ZnO nanorods (NRs) and discuss the potential for fast X-ray detection based on the consistent and efficient visible emission (~ 580 nm) from ZnO NRs. Nanostructured ZnO scintillators were rearranged to form a vertically well-aligned NR design in order to help light absorption and coupling resulting in luminescent and fast scintillation properties. The design of the nanorod array combines the key advantages of a low-cost growth technique together with environmentally friendly and widely available materials. A low temperature hydrothermal method was adopted to grow ZnO NRs in one cycle growth and their structural, optical and X-ray scintillation properties were investigated. The relatively short (~ 10 µm) ZnO NRs emitting in the near-band-edge region were found to be almost insensitive to X-rays. On the other hand, the higher XEL response of long ZnO NRs, which is a key parameter for evaluation of materials to be used as scintillators for high quality X-ray detection and imaging, along with a decay time response in the order of ns confirmed promising scintillation properties for fast and high-resolution X-ray detector applications.

Postsynthetic Modification of Hydrogen-Bonded Frameworks.

Hydrogen-bonded frameworks have garnered significant attention due to their flexible structures with tailored porosity, making them a promising class of porous framework materials. However, the direct synthesis of hydrogen-bonded frameworks with specific functions is highly challenging due to the unpredictable formation of hydrogen-bonded frameworks. In response, postsynthetic modification has emerged as a potent strategy to imbue desired functions into hydrogen-bonded frameworks. Recent advances have demonstrated the effectiveness of postsynthetic modification in hydrogen-bonded frameworks for studying their mechanical, luminescent, electrochemical, and chiral properties. In this concept, we comprehensively summarize the methodologies and outcomes of postsynthetic modification to hydrogen-bonded frameworks, providing a highlight of this exciting research area.

Investigation of luminescence properties of hydrothermally synthesized Pr3+ doped BaLuF5 nanoparticles under excitation by VUV photons

We report on the luminescence properties of hydrothermally synthesized BaLuF5:Pr3+(1%) nanoparticles having a cubic crystal structure. The properties were investigated at low temperatures using time-integrated and time-resolved luminescence spectroscopy under VUV photon excitation in the energy range of 5–45 eV. This spectral region covers both the Pr3+ 4f2→4f15d1 transitions and the intrinsic absorption of the host material. Due to the weak crystal field, only the intra-configurational Pr3+ 4f2→4f2 transitions were observed, resulting in photon cascade emissions. According to structural and morphological studies, the nanoparticles, with an average size of 21 ± 4 nm, were found to possess large amounts of defects, which are further confirmed through luminescence spectroscopy. The influence of non-radiative decay at the surface and energy transfer to the defects are responsible for the shortening of luminescence decay detected for the 1S0 transitions of Pr3+ ions and intrinsic UV cross-luminescence of host materials. We have discussed the specific energy transfer processes that populate various luminescence centers and evaluated BaLuF5:Pr3+(1%) nanoparticles for potential optical applications.

Impact of oxygen vacancy on luminescence properties of dysprosium-doped zinc oxide thin films

Pristine and dysprosium-doped ZnO thin films, highly c-axis oriented, were grown on a c-Al2O3 substrate using the pulsed laser deposition technique. During the deposition process, the growth was impacted by changes in the oxygen partial pressure. The structural, optical, and compositional properties of the pristine and dysprosium-doped ZnO thin films were systematically characterized using various state-of-the-art experimental techniques. The crystallinity associated with these films was observed to be highly dependent on the oxygen partial pressure maintained during the growth process. An average optical transparency of more than ∼90% in the visible spectral range (i.e., 400–800 nm) was observed for all specimens. For doped specimens, expected intra-4fn emissions of (dysprosium) Dy3+ ions that emanated from the 4F9/2 energy state were observed in room-temperature photoluminescence spectra under direct excitation. The Jacobian-transformed wavelength-to-energy plot for Dy-doped ZnO thin films in the UV-Visible region revealed intriguing findings. Specifically, it depicted a prominent peak at 2.82 eV, indicative of the energy state of Dy3+ ions, alongside intense band-edge emission and various defect-related emissions. The intensity of these transitions was observed to depend on the oxygen partial pressure kept during deposition. An x-ray photoelectron spectroscopy analysis of the doped specimen confirmed the +3 oxidation state of dysprosium into the ZnO matrix. These results provide a promising approach for controlling the doping and growth strategy of Dy-doped ZnO thin films, thereby opening up a wide range of applications and enhancement for next-generation optoelectronic devices.

DFT study of the role and possible contribution of defects to lithium metasilicate [formula omitted] luminescence

Lithium metasilicate (Li2SiO3) has recently been shown to display outstanding stimulated luminescence properties, which are governed by defects and/or impurities. Here, the possible contribution and character of native point and complex defects to stimulated luminescence of lithium metasilicate have been investigated employing calculations based on the density functional theory (DFT). Under high concentrations of acceptor defects, isolated lithium interstitials were found to be the defects with the lowest formation energy (0.41 eV) but it is shown that they cannot contribute to luminescence. On the other hand, Oi−2 are the most favorable and stable defects under high concentrations of donor defects. F-centers and oxygen peroxides were identified as first- and second-order processes of point defects, which would explain experimental observations in the literature. Bridging oxygen vacancies were shown to introduce shallow electron traps able to trap up to four electrons. On the contrary, non-bridging oxygen vacancies lead to the formation of deep color centers with the capability of trapping up to two carriers/center, which could be the final state for the radiative process of luminescence. These results provide guidance for the interpretation of experimental measurements of luminescence.

Thermochemistry of Solid-state Formation, Structure, Optical, and Luminescent Properties of Complex Oxides Eu2MeO6 (Me - Mo, W), Eu2W2O9: A Combined Experimental and DFT Study.

Complex oxides Eu2MeO6 (Me - Mo, W), Eu2W2O9 were obtained by a solid-phase reaction between binary oxides. The thermodynamic and kinetic mechanisms of the reaction processes were established using a variety of physical-chemical methods. All compounds obtained in this work crystallize in the low-symmetry monoclinic system, forming complex framework structures, which determine a set of very valuable physical-chemical properties. Comparison of experimental Kubelka-Munk functions and DFT- calculated absorption spectra shows adequate agreement and reveals the origin of the fundamental absorption. In addition, the deficiency in DFT calculations in the part of mutual contribution of CTBs of Mo-O and W-O, from one side, and Eu-O contributions, from the other side, is reported. Calculations of absorption spectra are shown to be superior to band structure analysis in the determination of optical band gaps. Additionally, luminescent properties of Eu2MeO6 and Eu2W2O9 compounds were investigated. These studies provide a better understanding of the electronic and optical properties of the compounds Eu2MeO6 and Eu2W2O9, along with their potential applications in various areas.

Modulation of Intermolecular Interactions in Organic Emitters for Highly Efficient Organic Light-Emitting Diodes.

The adverse aggregated-caused quenching (ACQ) problem of most electroluminescent materials existing in highly doped thin films is one of the key factors impeding the commercialization of high-efficiency organic light-emitting diodes (OLEDs) panel. Whereas, by delicately constructing and modulating moderate intermolecular interactions, some aggregates have been demonstrated to present distinct luminescent properties such as tunable emission spectra, improved photoluminescence quantum yields, different emission mechanism and enhanced horizontal transition dipole ratio (Θ) of emitting layer, providing feasible solution for ACQ problem. The luminescence from newly generated emissive state in aggregates is different from the traditional "isolated" molecules in organic electronics and will possess novel properties and applications. Herein, we summarize the different types of intermolecular interactions within emitter aggregates exhibiting distinct luminescent mechanisms, as well as their effects on photoluminescent and electroluminescent properties, offering reliable reference for the advancement of highly efficient OLEDs utilizing aggregated emitters.

Generation of pyridinylethylidenemalononitrile cyclic dimer: A facile route to multi-stimuli-responsive far-red/NIR luminogens

A simple synthetic strategy was successfully employed to develop NIR luminophores with switchable color-contrasting luminescence properties. D-A molecular motifs with dicyanovinylene appended pyridinyl moiety as the electron-withdrawing unit was not reported among luminescent molecules so far, owing to its unstable precursor compound pyridinylethylidenemalononitrile. By modifying the Knoevenagel condensation reaction pathways, the present work succeeded for the first time in identifying and crystallizing a novel cyclic dimerization product of the precursor compound. It further reports a new, simple, efficient synthetic route to achieve push-pull far-red/NIR emissive luminophores with the dicyanovinylene appended pyridinyl skeleton as the potent electron withdrawing unit. The enhanced charge transfer and the acidochromic characteristics make them suitable candidates in multi-stimuli-responsive smart materials with anti-counterfeiting applications.

Investigations on the photoelectric properties of the Mn doped inorganic CsSnCl3 perovskite

Mn dopant significantly improves the photoluminescent performance of CsSnCl3. To find the exact interactions induced by Mn dopant into the CsSnCl3 crystal, we studied the geometric, electronic and excitonic properties for these systems. We found an increased formation energy of the VSn defect, which promoting the stability and the luminescence properties of CsSnCl3 accordingly. Via analyses from the crystal field theory and the COHP calculations, we revealed that the transition of the 3d orbital of Mn2+ ion from 4T1→6A1 plays a crucial role in enhancing the luminescence of CsSnCl3. Also, we show that with the introduction of Mn dopant, the exciton binding energy increases, generating the more tight bounding interactions between the electron and hole pairs which results in the higher luminescence efficiency. Therefore, our results show that Mn doping indeed enhances the photoluminescence properties of CsSnCl3 and facilitates its application in the field of light-emitting devices.

Orange-reddish emitting of trivalent samarium doped double perovskite Sr2LuNbO6 with high thermal stability for white-LED application

A series of trivalent samarium ions (Sm3+) doped double perovskite Sr2LuNbO6 (x at% Sm3+:Sr2LuNbO6, x = 0.5–15) phosphors have been prepared via high-temperature solid-state method. The structural characterization of these phosphors was conducted employing X-ray diffraction (XRD), XRD Rietveld refinement, scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Density functional theory calculations utilizing the Vienna ab initio simulation package (VASP) were employed to unveil the electronic structures, encompassing the band structure and density of states (DOS). Photoluminescence (PL) spectroscopy was employed to scrutinize the luminescent properties, while the thermal stability of the PL spectra was also evaluated. The most prominent emission peak, exhibiting an orange-reddish hue, was observed at 601 nm upon excitation at 406 nm. The quenching mechanism of Sm3+ ions within the Sr2LuNbO6 host lattice was identified as a dipole-dipole interaction, with the quenching concentration of 3 at%. Moreover, the phosphors demonstrated excellent thermal stability, with an activation energy (Ea) value of 0.126 eV. These findings collectively underscore the promising potential of Sm3+:Sr2LuNbO6 orange-reddish phosphors for applications in white light-emitting diodes (w-LEDs).

Enhanced stability of perovskite CsPbBr3 QDs via Synergetic encapsulation with ZnO nanocrystals and commercial polymer

Lead halide perovskite nanocrystals with attractive optical properties and low-cost production have emerged as a reliable and promising candidate for next-generation display applications. However, the preparation of optical devices while maintaining high performance in complex environments poses a prominent challenge. Herein, a flexible, stretchable and stable nanocomposite was fabricated through embedding CsPbBr3 QDs (PeQDs) into ZnO nanocrystals and polymer, leading to the enhancements of both stability and luminescence efficiency. This simple approach allows PeQDs own a uniform size of ∼14 nm. Optical characterization showed that the PeQDs size did not change after embedding ZnO nanocrystals, while these QDs exhibit a distinct green emission, with emission centering at 518 nm and narrow bandwidth of ∼20 nm. It was also found that the PeQDs/ZnO/EPDM nanocomposite maintained sufficient stability even after being left in an outdoor environment for 27 days, soaked in water for 60 h, and placed on a hot plate at 90 °C for 60 min. Besides, nanocomposite still maintain good luminescent properties even when stretched four times its original length. Furthermore, using this PeQDs/ZnO/EPDM nanocomposite, the synthesized white light emitting diode (WLED) exhibits a color gamut coverage rate of 129 % under standard NTSC, and 97 % under standard Rec.2020. By using this PeQDs/ZnO/EPDM encapsulation adhesive film, the absolute efficiency of solar cell can be improved by 0.23 %. This work highlights a new insight into defect passivation techniques for PeQDs by the utilization of heterogeneous structures provided by metal oxides.

NIR-II luminescence and temperature sensing properties based on double perovskite La2MgTiO6: Yb3+/Er3+/Ho3+ phosphor

The near-infrared-II (NIR-II) fluorescence thermometer based on rare earth-doped double perovskite is rarely. Herein, Er3+-Ho3+ and Yb3+ co-doped lead-free double perovskite La2MgTiO6 (LMTO) phosphors were synthesized by a conventional high temperature solid phase method. The phase purity and morphology of the samples were analyzed using XRD and FE-SEM. The NIR-II luminescence properties of LMTO: Er3+-Ho3+-Yb3+ phosphors were systematically investigated under laser irradiation at 980 nm. A NIR-II fluorescence thermometer was also designed based on non-thermal coupled energy levels originated from the 4I13/2 energy level of Er3+ and the 5I6 energy level of Ho3+. The maximum value of relative sensitivity (Sr) was 0.54 % at 513 K. Compared to visible thermometers (LMTO: Er3+-Yb3+ and LMTO: Ho3+-Yb3+), the NIR-II thermometers offer better temperature measurement capability and penetration depth. All the experimental results show that the NIR-II thermometer with a wider range and higher sensitivity has been realized, which puts forward a new idea for the design and optimization of NIR-II thermometers.

Spectroscopic analysis of defect-induced luminescent and dielectric properties of MgO-based composites on varying dopant concentration

In this novel study, we prepared MgO matrix composites reinforced with varying weight percent ZnO using a solid-state reaction (SSR) method at 500 °C. We aimedto explore the potentialof these composites for high-frequency electronic devices.We conducted a comprehensive structural analysis of these MgO-based composites using various spectroscopic and microscopic techniques. Thisinclusive analysis revealed the morphology, particle size, elemental composition, valence states of elements, and defects in the composites. The Rietveld refinement of XRD data confirmed the presence of binary phase and the phase % of the constituents of composites. XPS spectra demonstrated the isovalent character of Zn/Mg elements and the presence of low-coordinated oxygen ions at the surface of the composites. The UV–visible-based spectroscopic techniques (Absorption and Photoluminescence) further supported the presence of low-coordinated surface O2– ions and F-center defects that caused a significant reduction in the bandgap of the samples. Photoluminescence (PL) analysis suggested the passivation of F-center defects in composites. We also investigated the effect of ZnO concentration and multiple excitation energies on the site-specific localized F-center defects to understand the defect distribution in the composites relative to the host.The dielectric properties of ZnO/MgO composites were assessed through impedance spectroscopy. We observed a significant enhancement in the dielectric constant (∼ 28.69–32.60) of the composites compared to pure MgO (∼12.2) at 1 kHz. This enhancement along with the smaller impedance of the composites relative to the host, as endorsed by the PL results,suggests areduction in F-centers (electrical barriers). This exciting finding paves the way forthe synthesis of ceramic composites with excellent dielectric and optical properties, indicating their potential applications in high-frequency electronic devices.