Green Photoluminescence Research Articles

Synergy of photoluminescence emission and antibacterial activity of Ag-Cu2O nanocomposite

Conglomerate nanocomposites comprising metal and metal oxide hold significant potential for exhibiting properties that surpass the combined characteristics of their individual components, owing to the interactions occurring at the interfaces between the metal and metal oxide elements. In this study, we present the synthesis of Cu2O nanoparticles (NPs) (with diameters ranging from 40 to 53 nm) and Ag-Cu2O nanocomposites using an aqueous solution method at room temperature, employing varying concentrations of Ag NPs. Through optical absorption studies, we determined the optical band gap of Cu2O NPs in 0.5Ag-Cu2O, 1Ag-Cu2O, and 1.5Ag-Cu2O nanocomposites samples to be 2.13 eV, 2.25 eV, 2.34 eV, and 2.41 eV, respectively. The x-ray diffraction data are analysed using the Williamson–Hall technique and revealed noteworthy variations in microstructural characteristics such as strain and stress within the Cu2O nanocrystallites fabricated under different Ag concentrations. The nanocomposites amplified the intensities of violet-blue, blue, and green photoluminescence (PL) emissions, attributable to the interfaces between Ag and Cu2O, lattice mismatches, and the induced microstructural parameters lattice strain, and stress of Cu2O nanocrystallites. The enhanced PL intensities can be attributed to the influence of the local electric field on the Ag core composites. The Ag-Cu2O nanostructure exhibits potential applications in water purification technologies, while the PL emission properties and low band gap (∼2.13 eV) hold promising applications in optoelectronic devices. The antibacterial activities of Cu2O and Ag-Cu2O nanomaterials against Enterococcus faecalis and Escherichia fergusonii are examined using MH agar well plate diffusion methods. Here, Ag NPs enhance bactericidal effectiveness through enhanced interaction with bacteria and the release of Ag+ ions, while the Cu2O shell discontinuity on Ag NPs contributes to their unique antibacterial properties.

Hydrothermal syntheses, structures and photophysical properties of two lanthanide isonicotinic acid complexes

Two rare earth isonicotinic acid compounds [Y(HIA)2(H2O)4(NO3)](2NO3) ((1); HIA = isonicotinic acid) and [LaHg3Cl8(HIA)4] nnCl (2) were reported. Compound one features an isolated (0-D) structure, while compound two has a two-dimensional (2-D) structure. The rare earth ions are coordinated by eight oxygen atoms to display a square antiprismatic REO8 geometry. Compound one shows blue photoluminescence and it has CIE chromaticity coordinates of 0.2332 and 0.3104. The CCT of compound 1 is 13755 K. Compound two exhibits green photoluminescence and it has CIE chromaticity coordinates of 0.3663 and 0.6184. The CCT is 4997 K. Their band gaps are 2.86 and 3.12 eV.

Optical tunning of high-luminescent iodine-substituted CsPb2(Br0.84I0.16)5 under pressure

Metal halide compounds hold significant interest for optoelectronics, given their substantial potential for solar cells and light-emitting applications. Low-dimensional (0D, 1D, and 2D) metal halide perovskites or perovskite-like compounds exhibit various compositions with soft lattices and modular optical properties. Thus, the finding of new strategies to further improve such properties is a current research challenge. In this scenario, the 2D perovskite-like compound CsPb2Br5 has attracted attention due to its structural stability and favorable optical properties. This study presents the pressure-induced structural phase transitions of the iodine substituted CsPb2(Br0.84I0.16)5. This substitution induces strong green photoluminescence in single crystals at ambient conditions. High-pressure optical and synchrotron X-ray diffraction experiments reveal a tetragonal-tetragonal structural phase transitions around 1 GPa, while the photoluminescence emission is quenched around 2.7 GPa. Additionally, a new high-pressure orthorhombic phase is identified in the iodine-doped compound beyond 4.5 GPa. Further analysis of structural features prove that the pressure dependent photoluminescence behavior is directly related to structural distortions observed upon pressure increase.

On the glow of cremated remains: long-lived green photo-luminescence of heat-treated human bones.

The long-lived green luminescence of human bone (that has been heated to 600°C for a short duration) is attributed to a carbon quantum dot material (derived from collagen) encapsulated and protected by an inorganic matrix (derived from bone apatite) and is more intense in dense rigid and crystalline parts of (healthy) human bones. The strong collagen-apatite interaction results (upon decomposition) in a protective inorganic environment of the luminescent centers allowing long-lived triplet-based emission of a carbon (quantum) dot-like material at room temperature, as well as resilience against oxidation between 550 and 650°C. The graphitic black phase (obtained upon heating around 400°C) is a precursor to the luminescent carbon-based material, that is strongly interacting with the crystalline inorganic matrix. Human bone samples that have been heated to 600°C were subjected to steady-state and time-resolved spectroscopy. Excitation-emission matrix (EEM) luminescence spectroscopy revealed a broad range of excitation and emission wavelengths, indicating a heterogeneous system with a broad density of emissive states. The effect of low temperature on the heat-treated bone was studied with Cryogenic Steady State Luminescence Spectroscopy. Cooling the bone to 80K leads to a slight increase in total emission intensity as well as an intensity increase towards to red part of the spectrum, incompatible with a defect state model displaying luminescent charge recombination in the inorganic matrix. Time-resolved spectroscopy with an Optical Multichannel Analyzer (OMA) and Time Correlated Single Photon Counting (TCSPC) of these samples showed that the decay could be fitted with a multi-exponential decay model as well as with second-order decay kinetics. Confocal Microscopy revealed distinct (plywood type) structures in the bone and high intensity-fast decay areas as well as a spatially heterogeneous distribution of green and (fewer) red emissive species. The use of the ATTO 565 dye aided in bone-structure visualization by chemical adsorption. Conceptually our data interpretation corresponds to previous reports from the material science field on luminescent powders.

Single CsPbBr3 Perovskite Microcrystals: From Microcubes to Microrods with Improved Crystallinity and Green Emission.

All-inorganic perovskite materials are promising in optoelectronics, but their morphology is a key parameter for achieving high device efficiency. We prepared CsPbBr3 perovskite microcrystals with different shapes grown directly on planar substrate by conventional drop casting. We observed the formation of CsPbBr3 microcubes on bare indium tin oxide (ITO)-coated glass. Interestingly, with the same technique, CsPbBr3 microrods were obtained on (3-Aminopropyl) triethoxysilane (APTES)-modified ITO-glass, which we ascribe to the modification of formation kinetics. The obtained microcrystals exhibit an orthorhombic structure. A green photoluminescence (PL) emission is revealed from the CsPbBr3 microrods. Contact angle measurements, Fourier-transform infrared and PL spectroscopies confirmed that APTES linked successfully to the ITO-glass substrate. We propose a qualitative mechanism to explain the anisotropic growth. The microrods exhibited improved PL and a slower PL lifetime compared to the microcubes, likely due to the diminished occurrence of defects. This work demonstrates the importance of the substrate surface to control the growth of perovskite single crystals and to boost the radiative recombination in view of high-performance optoelectronic devices.

Synthesis and resolution of multi-chiral carbonyl-N embedded hetero[7]helicenes for efficient circularly polarized luminescence.

Novel carbonyl-N embedded hetero[7]helicene diastereomers incorporating axially chiral binaphthyl were facilely synthesized and separated. The separated homochiral hetero[7]helicenes exhibit intense green photoluminescence and circularly polarized luminescence (CPL) with luminescence dissymmetry factors (glum) of 1.4 × 10-3 due to the intrinsic helical multiple-resonance skeleton.

Cold sintering of CsPbBr3 quantum dots embedded KBr ceramics for LED displays

Thanks to their tunable luminescence, narrow emission range, and superior color fidelity, perovskite quantum dots (PeQDs) are widely considered as promising materials for next-generation backlight displays. However, the susceptibility to degradation and failure when exposed to ambient environment significantly hampers their widespread applications. Herein, we reported an effective strategy to encapsulate CsPbBr3 nanocrystals into robust KBr matrix via cold sintering process at 120 °C. The well prepared translucent CsPbBr3@KBr ceramic displays a narrow green photoluminescence (with a full-width at half-maximum of ∼22 nm) and an quantum yield of 73.6% with remarkable thermal stability. By incorporating red emitting K2SiF4:Mn4+ phosphor into the KBr matrix, the color gamut of the constructed white LED improves to 118% of the National Television System Committee (NTSC) standard, suggesting that the thermally robust and narrow-band green emitter holds significant promise for wide-color-gamut liquid crystal displays.

Lead‐Free Perovskites with Photochromism and Reversed Thermochromism for Repeatable Information Writing and Erasing

AbstractRecently, novel optical information writing strategies have been developed based on fluorescent change of halide perovskites generated by light induced structural transformation. However, to date, the repeatable writing and erasing of fluorescent patterns are still a major challenge. Herein, lead‐free Cs3InCl6:Sb3+ perovskite with photochromism and reversed thermochromism is developed for repeatable information writing and erasing. The original Cs3InCl6:Sb3+ perovskite synthesized by a modified hot‐injection method exhibits green photoluminescence (PL), which is caused by recombination of self‐trapped excitons. After treating with ultrasonication and heating, the green PL gradually turns to blue emission, which is related to surficial Cl vacancies that are generated or exposed due to the desorption of surfactants. Under continuous UV light irradiation, due to the photo repairing effect, the blue emission gradually vanishes, the fluorescent color recovers to green. Based on this photochromic effect, fluorescent patterns are drawn by UV exposure with mask. Moreover, the green PL color can again return to blue by heating at 100 °C. Thus, the photochromism‐induced fluorescent patterns can be simply erased based on the reversed thermochromism effect. Therefore, repeatable optical information writing and thermal erasure are demonstrated based on reversible PL change of Cs3InCl6:Sb3+.

Kinetically Controlled Self-Assembly of Ag Nanoclusters with Enhanced Luminescence.

Constructing self-assembly with definite assembly structure-property correlation is of great significance for expanding the property richness and functional diversity of metal nanoclusters (NCs). Herein, a well-designed liquid reaction strategy was developed through which a highly ordered nanofiber superstructure with enhanced green photoluminescence (PL) was obtained via self-assembly of the individual silver nanoclusters (Ag NCs). By visual monitoring of the kinetic reaction process using time-dependent and in situ spectroscopy measurements, the assembling structure growth and the structure-determined luminescence mechanisms were revealed. The as-prepared nanofibers featured a series of advantages involving a high emission efficiency, large Stokes shift, homogeneous chromophore, excellent photostability, high temperature, and pH sensibility. By virtue of these merits, they were successfully employed in various fields of luminescent inks, encryption and anticounterfeiting platforms, and optoelectronic light-emitting diode (LED) devices.

Introduction of Electron Donor Groups into the Azulene Structure: The Appearance of Intense Absorption and Emission in the Visible Region.

In this work, through the Suzuki-Miyaura cross-coupling reaction with high yields, new π-conjugated azulene compounds containing diphenylaniline groups at positions 2 and 6 of azulene were synthesized. The obtained diphenylaniline-azulenes have intensely visible-light absorbing and emitting (in the wavelength range from 400 to 600 nm) properties. It has been shown that such unique optical properties, in particular fluorescent emission in the region of blue and green photoluminescence (λem at 495 and 525 nm), which were absent in the original azulene, are the result of the electron donor effect of diphenylaniline groups, which significantly changes the electronic structure of azulene and leads to the allowed HOMO → LUMO electron transition.

Aliphatic hyperbranched polyphosphate: a novel multicolor RTP material with AIE character.

Long-lived photoluminescent probes are emerging as significant luminogens for biological imaging. However, currently, most long-lived luminescent materials contain expensive rare elements or cytotoxic bulky aromatic or conjugated units. Herein, a novel hyperbranched polyphosphate (HBPPE) was synthesized using triethyl phosphate (TEP) and ethylene glycol (EG) through a transesterification polycondensation reaction. The obtained HBPPE P1 can emit bright blue photoluminescence under UV light and show significant AIE character. Interestingly, the average photoluminescence lifetime of P1 is 12.82 μs. This suggests the first phosphorescent material without rare elements or aromatic structures attributed to the covalent-crystal-like structure. Besides, P1 shows an obvious red-shift along with the excitation wavelength, which emits blue, cyan, green, yellow and red photoluminescence, covering nearly all the visible light region. This study not only enriches the species of nonconventional multicolor AIE luminogens but also provides a concise method for the synthesis of HBPPE and demonstrates the possibility for phosphorescent materials without rare elements or bulky aromatic units.

Detection of sulphur(II) of carbon dots synthesized from Gardenia residue.

The detection of anions using carbon dots (CDs) has received less attention compared to cations. Therefore, the present study aimed to develop a fluorescence sensor based on carbon dots (CDs) capable of detecting S2- in real water samples. The CDs were successfully prepared from the residues of a traditional Chinese herb, Gardenia, which emitted green photoluminescence (PL) under ultraviolet light irradiation. The as-prepared CDs were quasi-spherical in shape and ranged in size from 10 to 30 nm. Different detailed analyses proved that the CDs had good morphology, various functional groups, high water solubility, great optical features, and excellent stability under diverse environmental conditions. The ion detection showed that only Ag+ had the strongest fluorescence quenching effect on the CDs, however, the addition of S2- could recover their fluorescence. Based on these results, an "off-on" fluorescence sensor was achieved to selectively detect the concentration of S2- in real water samples with a limit of detection (LOD) of 39 μM, which further expanded the application of residues from traditional Chinese herbal medicine.

Thermally stable luminescence and dosimetric features of Ho(III) activated tungstate double perovskite

Luminescent efficient tungstate double perovskites Ca3WO6 doped with Ho3+ were synthesized via the solid-state reaction at 1200 C°. The resulting phosphors were analyzed using Rietveld refinement of X-ray diffraction (XRD) data, confirming a monoclinic crystal structure with crystallite sizes ranging between 50 and 55 nm. Optical bandgap determination was facilitated by diffusion reflectance spectra (DRS). Fourier transform infrared (FTIR) studies were conducted to identify functional group vibrations. The optical excitation of the Ca3WO6:Ho3+ phosphors under different excitation conditions resulted in intense green photoluminescence (PL) emission at 545 nm, indicative of the 5F4–5I8 transition of Ho3+ ions. Thermal stability assessment of Ca3WO6:1 % Ho3+ phosphor under blue excitation (454 nm) revealed good thermally stable luminescence about 85.32 % at LED working temperature (150 °C). PL decay studies were conducted to analyze fluorescent behaviour, wherein by means of PL decay lifetime, the PL quantum efficiency of Ca3WO6:1 % Ho3+ phosphor is computed to be 91.1 %. The CIE color coordinates of the phosphors being investigated reside within the green spectral region, with a calculated color purity of 93.25 % observed for Ca3WO6:1%Ho3+. Furthermore, the phosphors under study exhibited high-quality thermoluminescence (TL) after beta irradiation. The detailed TL characterization conducted to assess dosimetric properties. The impact of Ho3+ concentrations and beta dose on TL intensity are two major aspects that have been investigated in detail. TL fading experiments were performed to determine dose storage capacity over a month after beta irradiation. Additionally, the various heating rate (VHR) experiments are conducted to determine the TL kinetic parameters. Besides, the glow curve deconvolution (GCD) for trap parameter determination is also applied, where the results obtained are comparable with the VHR results.

Hole Relaxation Bottlenecks in CdSe/CdTe/CdSe Lateral Heterostructures Lead to Bicolor Emission.

Concentric lateral CdSe/CdTe/CdSe heterostructures show bicolor photoluminescence from both a red charge transfer band of the CdSe/CdTe interface and a green fluorescence from CdSe. This work uses visible and near-infrared transient spectroscopy measurements to demonstrate that the deviation from Kasha's rule arises from a hole relaxation bottleneck from CdSe to CdTe. Hole transfer can take up to 1 ns, which permits radiative relaxation of excitons remaining in CdSe. Simulations indicate that the hole relaxation bottleneck arises due to the sparse density of states and poor spatial overlap of hole states at energies near the CdSe band edge. The divergent kinetics of transfer for band edge and hot holes is exploited to vary the ratio of green and red photoluminescence with excitation wavelength, providing another knob to control emission color. These findings support the use of lateral heterojunctions as a method for slowing carrier relaxation in two-dimensional materials.

Highly Bright and Stable CsPbX3@Cs4PbX6 Hexagonal Nanoarchitectonics Created by Controlling Dissolution-Recrystallization of CsPbX3 Nanomaterials.

CsPbBr3@Cs4PbBr6 hexagonal NCs with a bright photoluminescence (PL) peak of 456nm are created through the dissolution-recrystallization of CsPbBr3 nanoplatelets. Small CsPbBr3 nanocrystals are encapsulated in hexagonal Cs4PbBr6 during recrystallization to form a core-shell structure and keep high brightness and stability. The recrystallization kinetics is systematically investigated to explore the roles of methyl acetate, oleylamine, and n-hexane. Result further indicates that core/shell NCs remained high PL under a variety of harsh conditions (e.g., light irradiation and heat treatment) because of Cs4PbX6 shell and the controlling of recrystallization. Their initial PL intensity is remained after 4 months of storage under ambient conditions and continuous exposure to UV lamp for 180min. The bright PL is also maintained even treatment at 120°C. To indicate the universality of this synthesis method, CsPbX3@Cs4PbX6 hexagonal NCs with different emission colors are fabricated by changing temperature, solvent viscosity, and precursors (e,g, oleylamine and halogens). These core-shell samples reveal bright and stable green, orange, and red PL. Because of its high stability, the core/shell NCs are dispersed in flexible films to create diverse patterns. The films also exhibit high brightness and excellent stability. This strategy opens a novel avenue for the application of perovskite nanomaterials in the display field.

Graphene nanosheet reinforcement of polyurethane nanocomposite for green and sustainable photoluminescence, superhydrophobic, and anticorrosive paint.

A simple and environmentally friendly method was developed for smart and efficient waterborne polyurethane (PUR) paint. Sugarcane bagasse was recycled into reduced graphene oxide nanosheets (rGONSs). Both lanthanide-doped aluminate nanoparticles (LAN; photoluminescent agent, 7-9nm) and rGONSs (reinforcement agent) were integrated into a waterborne polyurethane to produce a novel photoluminescent, hydrophobic, and anticorrosive nanocomposite coating. Using ferrocene-based oxidation under masked circumstances, graphene oxide nanosheets were produced from sugarcane bagasse. The oxidized semicarbazide (SCB) nanostructures were integrated into polyurethane coatings as a drying, anticorrosion, and crosslinking agent. Polyurethane coatings with varying amounts of phosphor pigment were prepared and subsequently applied to mild steel. The produced paints (LAN/rGONSs@PUR) were tested for their hydrophobicity, hardness, and scratch resistance. Commission Internationale de l'éclairage (CIE) Laboratory parameters and photoluminescence analysis established the opacity and colourimetric properties of the nanocomposite coatings. When excited at 365 nm, the luminescent transparent paints emitted a strong greenish light at 517 nm. The anticorrosion characteristics of the coated steel were investigated. The phosphor-containing (11% w/w) polyurethane coatings displayed the most pronounced anticorrosion capability and long-persistent luminosity. The prepared waterborne polyurethane paints were very photostable and durable.

HfTiO4 transparent thick film phosphors activated with Eu3+, Dy3+, and Tb3+ ions

Hafnium (Hf)-based double oxides show promise as high-efficiency scintillators due to large effective atomic numbers and high relative density. However, the preparation of these scintillation crystals is challenging due to their high melting points and incongruent melting behavior. In the present study, we demonstrated that the chemical vapor deposition (CVD) of single-phase HfTiO4 films on quartz glass substrate was successfully deposited at temperatures ranging from 973 to 988 K, with a TiO2 molar ratio in the precursor vapor of 25–45 mol% TiO2. The deposition rate of HfTiO4 reached 36 µm h−1. The films exhibited an in-line transmittance of 78 % relative to the raw glass substrate at a wavelength of 600 nm. When activated with Eu3+, Dy3+, and Tb3+ ions, the HfTiO4 films displayed red, yellow, and green photoluminescence emissions originated from the 4f–4f transitions of each trivalent rare-earth ion under ultraviolet light irradiation. HfTiO4 exhibited no intrinsic background emission, suggesting that the addition of a selected activator could yield a phosphor with the desired emission color range.

Oligomerization of dibrominated aminophenol on the basis of the chemical and HRP-catalyzed oxidative processes: Characterization and photoluminescence properties

Preparation of oligo (aminophenols) was carried out by chemical oxidative and enzymatic oligomerization of 4-amino-2,6-dibromophenol (ADBP). The former method required hydrogen peroxide as catalyst in an aqueous sodium hydroxide solution and the latter method was catalyzed by an enzyme, horseradish peroxidase, in 1,4-dioxane resulting in the formation of (ADBP)-ox and (ADBP)-enz, respectively. For the structural confirmation for both of the synthesized oligomers were fulfilled using FT-IR, UV–vis and 1H NMR and 13C NMR instruments. The chemical oxidation with H2O2 induced monodisperse particles in the sub-micron size. The thermal treatment of the oligomers at 1000 οC showed that the chemical oxidation resulted in (ADBP)-ox with higher residue% compared to enzymatic oxidation. Neutral ADBP underwent facile oxidation, leading to the formation of its corresponding oligomers, which were composed of head-to-tail or ortho-coupled constitutional moieties with lower optical and electrochemical band gaps than those of ADBP using two oligomerization routes. By analyzing the solvent effect on the absorption, lower optical band gaps of the synthesized oligomers were obtained in some selected solvents, pointing out them as semi-conductive material for the production of optoelectronic and electronic materials. By tuning the excitation wavelength, the fluorescence intensity of both of the oligomers was changed. DMF solution of (ADBP)-ox and (ADBP)-enz had a quantum yield of 17.6 % and 1.2 % for green and orange photoluminescence emission, respectively, with excellent photostability.

Li+ doped SrAl2O4:Eu2+, Dy3+ long‐persistent luminescence aluminoborosilicate glass‐ceramics: Preparation and properties

AbstractIn the SrO‐Al2O3‐B2O3‐SiO2 glass system, a SrAl2O4:Eu2+, Dy3+ long‐persistent luminescence glass‐ceramic (SAGC) with Li2O was successfully synthesized for the first time using the recrystallization‐melting method. The composition, micromorphology, long‐persistent luminescence (LPL) properties, photoluminescence (PL) properties, and water resistance were measured by X‐ray diffractometer, scanning electron microscope, brightness meter, fluorescence spectrophotometer, and pH meter, respectively. The method involves the formation of grains below the glass transition temperature, followed by the formation of the glass phase at a higher temperature, and finally the formation of products through cooling. The samples exhibited green PL and LPL emissions and demonstrated excellent color purity, homogeneity, and LPL luminescence. After doping Li2O, the purity and crystallinity of the SrAl2O4 were improved, and scalene hexagonal or monoclinic prismatic SrAl2O4 crystals with high regularity were synthesized in the glass matrix. This research indicates that excellent LPL benefits from the complete crystal structure, abundant crystals, and large crystal size. When the Li2O content reached 5 mol%, the crystal size was ∼30 µm, the PL and LPL properties performed best, and greater water resistance was exhibited. The SAGC in this new glass system has potential in optical storage.

Nitrogen vacancy–acceptor complexes in gallium nitride

We used photoluminescence (PL) spectroscopy and first-principles calculations to investigate GaN doped with Mg, Be, and implanted with Ca. The PL spectra revealed distinct red emission bands (RLA, where A = Be, Mg, and Ca) with maxima between 1.68 and 1.82 eV, each associated with a specific impurity. These bands consistently appeared alongside the green GL2 PL band at 2.33 eV, attributed to nitrogen vacancy (VN). Our calculations suggest that these bands result from recombination via defect complexes of group-II acceptors substituting for Ga with VN (AGaVN, A = Be, Mg, and Ca). The experimental +/0 transition levels for these complexes were estimated to be 0.6, 0.8, and 1.0 eV above the valence band maximum for Mg-, Be-, and Ca-containing complexes, respectively. The radiative recombination is facilitated by excited donor states located close to the conduction band minimum. Furthermore, our theory predicts that ZnGaVN and CdGaVN are stable and possess similar properties, although, no PL was detected from these defect complexes. The presented findings shed light on the identity of compensating donor complexes that impede the efficiency of p-type doping in GaN.