Intense Green Luminescence Research Articles

Assembly of a New 2D Heterometallic 3d–4f Coordination Polymer Bearing Planar Tetranuclear Square Building Blocks

A new two-dimensional (2D) 3d–4f heterometallic coordination polymer, which is {[Tb2Zn4(µ3-TFMIDC)4(µ4-HTFMIDC)(H2O)8]·2H2O}n, has been successfully synthesized by the solvothermal reaction of 2-(trifluoromethyl)-1H-4,5-imidazole dicarboxylic acid (H3TFMIDC) with Zn(II) and Tb(III) ions. The title compound was structurally characterized by diverse characterization techniques including single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Single-crystal structure analysis reveals that the as-preprared compound is a 2D heterometallic 3d–4f coordination network based on interesting planar tetranuclear squares [Zn4(TFMIDC)4] as building blocks, representing the first example of novel heterometallic coordination polymer based on the H3TFMIDC ligand. In addition, the title compound exhibits very intense green luminescence and characteristic transitions of the Tb(III) ion when excited at 291 nm. Lattice parameters for the title compound: a = 11.1449(12) A, b = 12.8498(13) A, c = 37.553(4) A, α = β = γ = 90°, V = 5378.0(10) A3, Z = 4. A unique 2D 3d–4f heterometallic coordination polymer containing interesting planar tetranuclear square building blocks has been constructed by the solvothermal reaction of 2-(trifluoromethyl)-1H-4,5-imidazole dicarboxylic acid (H3TFMIDC) with Zn(II) and Tb(III) ions.

Reliable temperature sensing based on intense green upconversion emissions of Y2Mo4O15:Yb3+,Er3+ under 980 nm excitation

In this paper, Y2Mo4O15:Yb3+/Er3+ upconversion phosphors are prepared by a co-precipitation method. In the case of 20% Yb3+ doping, the intense green upconversion luminescence is obtained, which can be attributed to the energy transfer from Yb3+-MoO42- dimer to Er3+ that suppresses the multi-phonon relaxation of 4I11/2 to 4I13/2. Similar the Yb3+ sensitization, the dimer sensitization is also dependent on the Yb3+ concentration. When the Yb3+ concentration exceeds 20%, the luminescence is quenched by the cross relaxation and energy migration between dimers. A method for evaluating the reliability of temperature measurement standards is reported. Moreover, in term of the reliable temperature scale, the maximum absolute sensitivity of sample doped with 20% Yb3+ is determined to be 0.0117 K-1. Favorable sensing ability and strong upconversion luminescence indicate that the optimum sample is potentially applicable as the optical thermometric materials.

Calibration of optical temperature sensing of Ca1-xNaxMoO4:Yb3+,Er3+ with intense green up-conversion luminescence

High luminescence intensity is crucial for realizing luminescent temperature sensing with a large signal-to-noise ratio. In this work, the temperature sensing behavior of Ca1-xNaxMoO4:Yb3+,Er3+ with intense green up-conversion luminescence was studied. It has been demonstrated that the single-band green emission was dependent on the Yb3+-MoO42- dimer sensitization as well as the low multi-phonon relaxation rate of 4S3/2 → 4F9/2. In addition, it was found that the uncorrected thermometer could not accurately measure temperature due to thermal effects. A simple method for calibration of up-conversion temperature sensing was reported. Due to high luminescence intensity and temperature sensitivity, Ca1-xNaxMoO4:Yb3+,Er3+ is a promising candidate for up-conversion temperature sensing.

Two Novel Binuclear Lanthanide Complexes with 2,5‐Dichlorobenzoic Acid and 5,5’‐Dimethyl‐2,2’‐bipyridine: Crystal Structures, Luminescence and Thermal Properties

AbstractTwo novel binuclear lanthanide complexes [Ln(2, 5‐DClBA)3(5,5’‐DM‐2,2’‐bipy)(H2O)]2(5,5’‐DM‐2,2’‐bipy) (Ln=Eu(1), Tb(2)); 2,5‐DClBA=2,5‐dichlorobenzoate; 5,5’‐DM‐2,2’‐bipy=5,5’‐dimethyl‐2,2’‐bipyridine) have been successfully synthesized via conventional solution method and then characterized by single‐crystal X‐ray diffraction and elemental analysis. These two binuclear complexes differ from other reported binuclear complexes, because the free neutral ligands are not common in crystal structure. The complexes are isomorphic, which have the same coordination number of eight with a distorted square antiprismatic molecular geometry. The binuclear units feature hydrogen bonding (O−H⋅⋅⋅N and C−H⋅⋅⋅Cl) and π‐π stacking interactions assemble the adjacent molecular units into 1D, 2D and 3D supramolecular novel structures. It is worth noting that the novel 1D supramolecular structure is formed by the hydrogen bonding interaction between the nitrogen atoms of free 5,5’‐DM‐2,2’‐bipy ligand and the oxygen atom of the coordination water molecule. The thermal decomposition mechanism of the two complexes were studied by TG/DSC‐FTIR techniques. Additionally, the luminescence spectra and lifetime have been studied in detail. The results indicate that Eu3+ ion and Tb3+ ion could be sensitized by ligands and thus emitted intense characteristic red and green luminescence, respectively.

Ratiometric Fluorescence Platform Based on Modified Silicon Quantum Dots and Its Logic Gate Performance.

A novel optical nanoprobe based on silicon quantum dots (SiQDs) has been assembled through a one-pot low-temperature (40 °C) treatment by using 3-(aminopropyl)trimethoxysilane (APTMS) and ascorbic acid (AA) as two precursors. The water-soluble SiQDs demonstrate intense green luminescence in aqueous environment and the excitation-dependent feature has been explored. Meanwhile, the incorporation of salicylaldehyde (SA) serves to suppress the emission of SiQDs effectively via nucleophilic reaction and an "on-off" change is observed. Furthermore, the addition of Zn2+ can lead to evolution of emission peaks, and the green band at 500 nm gradually shifts toward the blue side at 455 nm. The corresponding ratiometric signal changes ( I455/ I500) can accurately determine the Zn2+ concentration and the limit of detection is calculated to be 0.17 μM in the linear range between 1 and 100 μM. In this research, a molecular logic gate (AND) system has been well established by using SA and Zn2+ as two inputs. The fluorescence emission changes based on SiQDs will shed new light on the development of functional sensors at the nanoscale level.

A Bio-design of Superhydrophobic Nano-coating from ZnO and Studies of Its Green Photoluminescence Inspired by Lotus Leaf

Inspired by green lotus leaf, we bio-designed a superhydrophobic gel nanocoating with green photo-luminescence. The ZnO ingredient was prepared by sol-gel method and then modified with stearic acid (STA) to obtain superhydrophobic nano-coating. The microstructures, wettability and photoluminescence of the ZnO were characterized by scanning electron microscopy, X-ray diffraction spectroscopy, contact angle analysis and fluorescence spectrophotometry. The experimental results of ZnO-STA show excellent superhydrophobicity on various substrates and intense green luminescence. These findings can open a new view for luminescent devices with self-cleaning advances.

RETRACTED: Luminescent Tb(III)-based coordination polymer: Selective detection of CS2 and anti-tumor activity in cardiac myoma

Abstract A new luminescent Tb(III)-based coordination polymer, namely [Tb2(tci)2(H2O)4]n·n(DMA) (1 H3tci = tri(2-carboxyethyl)isocyanurate, DMA = N,N′-dimethylacetamide), was constructed using a symmetrical tricarboxylate ligand. Single crystal X-ray structural analysis revealed that compound 1 features a 3D porous framework constructed from the linkage of tci3− ligands and chain-shaped building subunits. This compound displays intense characteristic green luminescence of Tb3+ at ambient temperature, and exhibits highly selective and sensitive luminescence response toward to CS2 molecule. In addition, the cytotoxicity of this Tb-MOF has been further probed via the MTT assay.

Axial Inhomogeneity of Mg-Doped GaN Rods: A Strong Correlation among Componential, Electrical, and Optical Analyses

We systematically characterized the inhomogeneous doping properties along the c-axis of Mg-doped p-GaN microrods. Axial variation of doping concentration and electrical resistance on the p-GaN rod were measured by time-of-flight secondary-ion-mass-spectrometry and four-point probe measurements, respectively. Defects-related optical information was obtained from photoluminescence spectra together with Raman experiments revealing the change of crystal quality and strain along the rod. On the basis of a correlation of these analyses, we confirmed that Mg concentration decreased along the axial direction of the rod, leading to increasing electrical resistance. This axial Mg concentration change was revealed by green luminescence because the intensity of green luminescence sensitively varied with the doping density in both high-doping and low-doping rods. Interestingly, all the resistances at the highly doped rods were higher than the lowly doped rods due to overall mobility degradation at the high-doping rods...

Cu(I) complexes regulated by N-heterocyclic ligands: Syntheses, structures, fluorescence and electrochemical properties

Three mononuclear Cu(I) complexes, namely, [Cu(2-PBO)(PPh3)2]·ClO4·2CH2Cl2 (1), [Cu(3-PBO)(PPh3)2(ClO4)]·CH2Cl2 (2) and [Cu(PBM)(PPh3)2]·ClO4 (3) (2-PBO = 2-(2′-Pyridyl)benzoxazole, 3-PBO = 2-(3′-Pyridyl)benzoxazole, PBM = 2-(2′-Pyridyl)benzimidazole, PPh3 = triphenylphosphine) have been synthesized and characterized by elemental analyses, IR, 1H NMR, 13C NMR, X-ray single crystal diffraction and thermal analysis. Photoluminescent investigation shows that complexes 1–3 exhibit distinct tunable light green (512 nm)-to-yellow (557 nm) photoluminescence by varying the N-heterocyclic ligands. Three complexes show intense 2-PBO-based yellow, 3-PBO-based light green and intense PBM-based bright green luminescence upon irradiation with a standard UV lamp (λex = 254 nm) at room temperature. Moreover, the electrochemical properties of 1–3 have been investigated by cyclic voltammetry. The results suggest the frontier molecular orbits and the HOMO-LUMO energy gaps of these cuprous complexes are effectively adjusted through the introduction of different N-heterocyclic ligands, thus achieving the selective luminescence of the cuprous complexes.

Luminescent properties of Tb3+- doped TeO2-WO3-GeO2 glasses for green laser applications

Different concentrations of Tb3+ -doped oxyfluoro tellurite (TWGTb) glasses were prepared by conventional melt quenching technique and characterized for green laser applications. The Judd-Ofelt theory was applied to evaluate various spectroscopic and radiative parameters. The TWGTb glasses exhibit 5D3 → 7F5-3 and 5D4 → 7F6-0 transitions when excited at 316 nm radiation. The variation of intensity of 5D4 → 7F5 (Green) and 5D3 → 7F4 (Blue) transitions and the green to blue (IG/IB) intensity ratios were studied as a function of Tb3+ ions concentration. The laser characteristic parameters such as effective bandwidth (Δλeff), stimulated emission cross-section (σe), gain bandwidth (σe × Δλeff) and optical gain (σe × τR) were determined using the three phenomenological Judd-Ofelt intensity parameters. The fluorescence decay profiles of 5D4 metastable level exhibit single-exponential nature for all the samples. Based on the experimental results we suggest that the 1.0 mol% of Tb3+ -doped TWGTb glass could be a suitable laser host material to emit intense green luminescence at 545 nm.

Emergence of Uranium as a Distinct Metal Center for Building Intrinsic X‐ray Scintillators

AbstractThe combination of high atomic number and high oxidation state in UVI materials gives rise to both high X‐ray attenuation efficiency and intense green luminescence originating from ligand‐to‐metal charge transfer. These two features suggest that UVI materials might act as superior X‐ray scintillators, but this postulate has remained substantially untested. Now the first observation of intense X‐ray scintillation in a uranyl–organic framework (SCU‐9) that is observable by the naked eye is reported. Combining the advantage in minimizing the non‐radiative relaxation during the X‐ray excitation process over those of inorganic salts of uranium, SCU‐9 exhibits a very efficient X‐ray to green light luminescence conversion. The luminescence intensity shows an essentially linear correlation with the received X‐ray intensity, and is comparable with that of commercially available CsI:Tl. SCU‐9 possesses an improved X‐ray attenuation efficiency (E>20 keV) as well as enhanced radiation resistance and decreased hygroscopy compared to CsI:Tl.

Efficient green luminescence of terbium oxalate crystals: A case study with Judd-Ofelt theory and single crystal structure analysis and the effect of dehydration on luminescence

Design and synthesis of Lanthanide based metal organic framework is a frontier area of research owing to their structural diversity enabling specific applications. The luminescence properties of rare earths, tuned by the structural features of Ln-MOFs are investigated extensively. Rare earth oxalates which can be synthesized in a facile method, ensuring the structural features of MOFs with excellent photoluminescence characteristics deserves much attention. This work is the first time report on the single crystal structure and Judd-Ofelt (JO) theoretical analysis – their correlation with the intense and sharp green luminescence of Terbium oxalate crystals. The intense green luminescence observed for Terbium oxalate crystals for a wide range of excitation from DUV to visible region despite the luminescence limiting factors are discussed. The absence of concentration quenching and lifting up of forbidden nature of f-f transitions, allowing direct excitation of Terbium ions is analysed with the help of JO theory and single crystal structure analysis. The JO analysis predicted the asymmetry of Terbium sites, allowing the electric dipole transitions and from the JO intensity parameters, promising spectroscopic parameters – emission cross section, branching ratio, gain band width and gain coefficient of the material were calculated. The single crystal structure analysis revealed the asymmetry of Tb sites and structure of Terbium oxalate is formed by the hydrogen bonded stacking of overlapped six Terbium membered rings connected by the oxalate ligands. The molecularly thick layers thus formed on the crystal surface are imaged by the atomic force microscopy. The presence of water channels in the structure and the effect of lattice water molecules on the luminescence intensity are also investigated.

Upconversion and Phase Transition Characteristics in Erbium(III)- and Ytterbium(III)-Codoped Vanadium(IV) Oxide

ABSTRACTVanadium(IV) dioxide has emerged as a promising thermochromic material for smart window application through metal–insulator transition, which simultaneously involves an abrupt change in optical, electrical, and magnetic properties. Here, Er3+ or Yb3+-codoped vanadium(IV) dioxide has been prepared by a hydrothermal and annealing process. The structure, metal–insulator transition, and upconversion luminescence characterizations have been evaluated using X-ray diffraction, differential thermal analysis, and fluorescence spectral analysis. The samples exhibit unique properties, including enhancing the intensity of upconversion emission, decreasing the metal–insulator transition temperature to 41.4°C, and emitting bright green upconversion emission along with extremely weak emission in the red region under 980 nm excitation. Moreover, green upconversion luminescence intensity increased by an order of magnitude from the low-temperature monoclinic structure of vanadium(IV) dioxide to the high-temperature rutile structure of vanadium(IV) dioxide for the first time, which will pave a new pathway for researching the application of photoluminescence in smart materials.

Upconversion Luminescent Material‐Based Inorganic‐Organic Hybrid Sensing System for the Selective Detection of Hydrazine in Environmental Samples

AbstractHydrazine is a noxious environmental pollutant, which can be easily absorbed through skin, respiratory and oral paths of exposure and leads to mutagenic and carcinogenic diseases, which demands for the progress of advanced detection methods. In this regard, we report a new detection platform based on luminescence resonance energy transfer (LRET) for the detection of hydrazine (N2H4) in environmental samples, where anti‐Stokes shift luminescence having optical sensing system is built with upconversion nanophosphors (UCNPs, donor) modified by resorufin propionate (RePr, acceptor). Herein UCNPs were used as an excitation host to significantly minimize the photobleaching of RePr. Upon interaction with N2H4, the green upconversion luminescence (UCL) intensity of hybrid nanoprobes (RePr‐UCNPs) gradually decreases, since the green emission is in resonance with the absorbance of resorufin, whereas the red emission intensity was intact. Hence, green emitting optical sensing system shows red luminescence in the presence of hydrazine. This organic‐inorganic hybrid sensing system has been utilized for the sensing of hydrazine in various environmental samples and the obtained results are compared with the sensing efficiency in distilled water. This anti‐Stokes shift luminescent hybrid sensing system would be a promising candidate to be utilized in environmental protection, water treatment and safety inspection.

Tunable CsPbBr3/Cs4PbBr6 phase transformation and their optical spectroscopic properties.

As a novel type of promising materials, metal halide perovskites are a rising star in the field of optoelectronics. On this basis, a new frontier of zero-dimensional perovskite-related Cs4PbBr6 with bright green emission and high stability has attracted an enormous amount of attention, even though its photoluminescence still requires to clarification. Herein, the controllable phase transformation between three-dimensional CsPbBr3 and zero-dimensional Cs4PbBr6 is easily achieved in a facile ligand-assisted supersaturated recrystallization synthesis procedure via tuning the amount of surfactants, and their unique optical properties are investigated and compared in detail. Both Cs4PbBr6 and CsPbBr3 produce remarkably intense green luminescence with quantum yields up to 45% and 80%, respectively; however, significantly different emitting behaviors are observed. The fluorescence lifetime of Cs4PbBr6 is much longer than that of CsPbBr3, and photo-blinking is easily detected in the Cs4PbBr6 product, proving that the zero-dimensional Cs4PbBr6 is indeed a highly luminescent perovskite-related material. Additionally, for the first time, tunable emissions over the visible-light spectral region are demonstrated to be achievable via halogen composition modulations in the Cs4PbX6 (X = Cl, Br, I) samples. Our study brings a simple method for the phase control of CsPbBr3/Cs4PbBr6 and demonstrates the intrinsic luminescence nature of the zero-dimensional perovskite-related Cs4PbX6 products.

A temperature-triggered triplex bistable switch in a hybrid multifunctional material: [(CH2)4N(CH2)4]2[MnBr4

Bistable optical-electrical duplex switches represent a class of highly desirable intelligent materials because of their potential applications in the fields of next-generation flexible devices. However, controllable photoelectric switchable materials with high-performance dielectric-switching and optical-switching properties are still scarce, with triplex bistable switches being rarely reported. Herein, a novel optoelectronic triple-functional organic-inorganic material, 5-azonia-spiro[4,4]nonane tetrabromomanganese (1, [ASN]2[MnBr4], ASN = (CH2)4N(CH2)4), which undergoes a reversible solid-state phase transition around 327 K and exhibits a recognizable second harmonic generation (SHG) effect between SHG-on and SHG-off states, has been successfully synthesized and grown as block crystals. Intriguingly, the bromine-doped crystal can exhibit intense green luminescence with a high quantum yield of 13.07% under UV excitation, extending its application in the field of photoelectric seamless integration and/or flexible multifunctional devices.

Photoluminescence and cathodoluminescence studies of Er3+-activated strontium molybdate for solid-state lighting and display applications

The photoluminescence and cathodoluminescence properties of erbium ion (Er3+) activated SrMoO4 phosphor have been investigated herein. The photoluminescence (PL) emission spectra, recorded within 400–800 nm wavelength range upon 380 nm UV light excitation exhibit unusual blue emission along with its well-known green luminescence which has been explained through underlying mechanisms with the help of energy level structure. The blue luminescence of the phosphor at various Er3+-concentrations was further confirmed by computing the spectral colour coordinates that lies in the blue region of the chromaticity diagram. The cathodoluminescence (CL) spectra which were measured under low voltage electron beam excitation exhibited intense green luminescence. The PL and CL studies carried out in the synthesized phosphor indicates that it can be a useful candidate for making UV-excited light emitting diodes (LEDs) and low voltage electron beam excited field emission displays (FEDs).

Transparent Perovskite Light-Emitting Touch-Responsive Device.

A light-emitting touch-responsive device (LETD) for instantaneous visualization of pressure mapping is reported. The LETD integrates an organometal halide perovskite polymer composite emissive layer and a flexible silver nanowire polyurethane composite transparent electrode. The composite emissive layer contains methylammonium lead bromide nanocrystals uniformly dispersed in a poly(ethylene oxide) (PEO) matrix and emits an intense green luminescence that peaks at 529 nm. The PEO matrix promotes the formation of small perovskite grains (∼20 nm) and a pinhole-free composite film with surface roughness of only 2.96 nm. The composite transparent electrode is separated from the emissive layer with a 100 μm thick spacer. When a local pressure is applied, a Schottky contact is formed instantaneously between the metal and the emissive layer, and electroluminescence is produced at voltages as low as 2.5 V and reaches 1030 cd/m2 at 6 V. The transparent LETD has approximately 68% transparency. It can be bent to a 6 mm radius when polyethylene terephthalate is used as the substrate. The perovskite LETD has fast response and can be pixelated to offer potential applications in robotics, motion detection, fingerprint devices, and interactive wallpapers.

Luminescence and Valence of Tb Ions in Alkaline Earth Stannates and Zirconates Examined by X-ray Absorption Fine Structures.

The difference in Tb3+ green luminescence intensities in doped perovskite(ABO3)-type alkaline earth stannates, AeSnO3 (Ae = Ca, Sr, Ba), and the Mg codoping effect on the luminescence intensities in doped CaMO3 (M = Sn, Zr) were investigated utilizing the X-ray absorption fine structures (XAFS) of the Tb LIII absorption edge. It is considered that the local symmetry at A sites is responsible for the different Tb3+ luminescence intensities in AeSnO3 (Ae = Ca, Sr, Ba) doped with Tb ions at A sites. However, it was found from the XAFS spectra that some Tb ions are unintentionally stabilized at B sites as Tb4+, especially in BaSnO3. Not only the central symmetry for Tb3+ at A sites but also the presence of Tb4+ at B sites were considered to bring about the absence of Tb3+ luminescence in doped cubic BaSnO3. No obvious changes in the Tb3+ local structure at A sites were detected between Tb single doped and Tb-Mg codoped CaMO3 (M = Sn, Zr) from the extended XAFS oscillation, but the trace of Tb4+ at B sites in the Tb single doped sample was observed in the X-ray absorption near edge structures. It is, therefore, considered that the Tb3+ luminescence enhancement by Mg codoping is primarily attributed to the charge compensation rather than the changes in the local structure around Tb3+ at A sites.

Tunable emission color of Gd2(MoO4)3:Yb3+, Ho3+, Tm3+ phosphors via different excitation condition

The methods of modulating emitting color are greatly important for up-conversion phosphors to broaden their applications, ranging from information storage to surface display. In this paper, the Ho3+/Tm3+/Yb3+ tri-doped Gd2(MoO4)3 phosphors are synthesized by typical sol-gel method. It is found that the phosphors can radiate intense blue (475 nm), green (542 nm) and red (660 nm) up-conversion luminescence under 980 nm or 915 nm laser excitation. Especially, the emission color of the phosphors can be tuned from red to lavender by adjusting the excitation power of 980 nm or 915 nm continuous lasers. In addition, the up-conversion luminescence is also investigated under the excitation of 980 nm pulse laser. The emission color varies from green to blue and green to yellow by altering the pulse width and frequency, respectively. Combining the above methods, multi-color and white light are realized, indicating the potential application in dynamic colorful display.