Intensive Luminescence Research Articles

Hazai képződményekből szeparált kvarcok jellemzői az OSL kormeghatározás szempontjából

Az OSL (Optically Stimulated Luminescence) kormeghatározás alkalmazása a Magyar Állami Földtani Intézetben 2004-ben kezdődött, majd a jogutód Magyar Földtani és Geofizikai Intézetben folytatódott, és a Magyar Bányászati és Földtani Szolgálatban jelenleg is folyik. A felső-pleisztocén és holocén üledékek OSL kormeghatározása során tett megfigyeléseink szerint a kvarcok lumineszcens tulajdonságai és OSL kormeghatározásra való alkalmassága helyi eltéréseket mutat. Ezeknek az eltéréseknek az okait kerestük. Vizsgáltuk a kvarc eltérő forráskőzeteinek hatását olyan kvarcgazdag magmás, metamorf és idősebb üledékes képződményekből nyert kvarcszeparátumokon, amelyek hazánkban jelenleg a felszínen is előfordulnak, és anyaguk a negyedidőszaki üledékbe is bekerülhetett. Az OSL mérések mellett a kvarcszemcsék kristályrács hibáit okozó szennyeződések kimutatására LA-ICP-MS, mikro-FTIR és IR spektrometriai méréseket alkalmaztunk. A kvarcszeparátumok pontosabb jellemzéséhez fénymikroszkópos vizsgálatot, valamint termoanalitikai és röntgen-pordiffrakciós elemzéseket végeztünk. A kvarcokat befoglaló képződmények radioaktív elemtartalmát gamma-spektrometriai mérések segítségével határoztuk meg.
 OSL mérési eredményeink alapján az üledékes képződmények és egyes vulkáni tufák kvarcszeparátumai fényesebb, nagyobb intenzitású lumineszcenciát adtak, mint a vizsgált metamorf és mélységi magmás kőzetek. Közvetlenül, az első mállási és szállítási ciklus után az üledékekbe kerülve csupán néhány üledékes képződmény kvarcszemcséi lennének alkalmasak a kormeghatározásra.
 A kvarcok OSL tulajdonságait meghatározó kristályrács hibáit az LA-ICP-MS vizsgálat szerint Li, Na, Al, P, K, Ti és Ba beépülése okozhatja, és a mikro-FTIR mérésekkel kimutatott, a Si4+ iont helyettesítő Al3+ + H+, azaz AlOH szerkezeti hidroxil, valamint molekuláris víz. A nagyobb intenzitású OSL-t adó kvarcszeparátumok befoglaló képződményei kisebb K- és Th-tartalommal rendelkeznek, mint a gyengébb OSL-t kibocsátóké.
 A negyedidőszaki üledékek kvarcainak lumineszcens tulajdonságaiban és OSL kormeghatározásra való alkalmasságában mutatkozó helyi eltérések oka az eltérő forráskőzeteik, valamint különböző hő- és üledékes történetük lehet. A mélységi magmás és metamorf kőzetek elsődleges lepusztulásából származó kvarcok kedvezőtlen OSL tulajdonságát az eredményezheti, hogy bár magas hőmérsékleten képződve sok kristályrács hiba alakult ki bennük, de azok nagy részét lassú kihűlésük során elvesztették. Az üledékes képződmények kvarcszemcséinek kedvezőbb OSL tulajdonságai elsősorban a szállításuk és áthalmozódásuk során az ismétlődő radioaktív besugárzási, azaz OSL felépülési, és napfényen az OSL lenullázódási ciklusoknak köszönhető, melyek növelik a kvarc lumineszcens érzékenységét.

Luminescent AlN:Mn nanoparticles for optical imaging of biological materials

Background: Elaboration of new luminescent nanomaterials for imaging of biological materials including cells of living organisms and their parts is highly actual. These materials must meet a number of requirements such as low toxicity, inherence of intensive luminescence, low costs of raw material and symple synthesis methods. AlN nanopowder is one of such prospective materials fitting the above requirements. Our long time investigations on spectral characteristics for III group element nitrides allows chose of doped AlN nanopowder as prospective candidate for developing of luminescent markers for imaging of biological materials. Objectives: The aim of the present study is spectral characterization of AlN nanopowder doped with Mn and evaluation of its use as luminescent marker for biological materials. Materials and methods: AlN nanopowder with average size of polycrystalline grains of 60 nm and the same doped with Mn were sythesized in Institue of Inorganic Chemistry, Riga Technical University. Photoluminescence and its excitation spectra of the materials were studied at room temperature using a self-made set-up. Results: It was found that in undoped AlN nanopowder at room temperature luminescence of native defects forms a wide and complex band peaking at 415 nm. This blue luminescence can be excited with ultraviolet light from two spectral regions around 315–340 nm and 260 nm. Two luminescence mechanisms are proposed dependent on the spectral region of exciting light. The first of them results in the intra-center luminescence, but the second one is recombination luminescence. Incorporation of Mn atoms in the crystalline lattice of AlN nanopowder forming AlN:Mn NP results in appearance of intensive red luminescence at 600 nm, which can be excited with light from two excitation bands at 260 and 480 nm. Two mechanisms responsible for an appearence of the red luminescence of Mn are proposed. They are the intra-center luminescence and recombination luminescence mechanisms. In this case the red Mn luminiscence prevails and the blue luminescence characterizing the host material has not been observed. Conclusion: AlN nanopowder doped with Mn atoms is a prospective material for use as luminescent marker for imaging of biological materials. Properties of this material are in a good agreement with the main requirements obligated to biological materials: i) AlN NP has low toxicity; ii) AlN:Mn NP possesses intensive red luminescence at 600 nm, which can be excited either with the ultraviolet light around 260 nm or with visible light around 480 nm; iii) it is relatively cheep material and it can be synthesized using simple synthesis methods.

Dual luminescence of polymers with grafted BF2-benzoylacetonate groups

Polymers with varied contents of BF2-benzoylacetonate (BF2-BAc) groups have been synthesized by the reaction of double acylation of copolymers of methyl methacrylate and styrene. The synthesized polymers have exhibited a dual luminescence: at λex = 365 nm, an intensive blue monomers luminescence with a maximum at 390 nm was observed, while at λex = 400 nm, an aquamarine luminescence of aggregates was registered at 450 nm. The polymer, in which the content of BF2-BAc groups equaled to 2.7%, has formed two modifications with different optical properties. Upon mechanical activation (grinding) and melting, one observes a transfer from the modification, in which BF2-BAc groups form aggregates, to the amorphous modification. Upon UV-irradiation of the amorphous samples, there occurs the formation of aggregates and excimers based on them present in the initial polymer. There is a possibility that the synthesized polymers can be used in creating smart materials applied in sensors, data recording and storage, rewritable carriers, and optoelectronic devices.

Ag/Na Ion Exchange in Fluorophosphate Glasses and Formation of Ag Nanoparticles in the Bulk and on the Surface of the Glass

Nanoscale silver clusters and metal Ag nanoparticles embedded in fluorophosphate glass were produced by Na/Ag ion exchange and subsequent heat treatment. The studied ion exchange was found to provide the reduction of Ag+ ions to Ag0 and formation of the small Ag2–4 clusters featuring intensive luminescence. Treatment at the temperatures 320–410 °C resulted in the appearance of two surface plasmon resonance (SPR) bands corresponding to large clusters Agn (n = 11–70) with blue-shifted plasmonic band and metal Ag nanoparticles. Two different SERS substrates were obtained by an out-diffusion technique. A silver nanoisland structure was grown after heat treatment in the oxygen atmosphere. The nanoporous Ag films with a rough surface were grown in hydrogen atmosphere. The nanoporous Ag film was used as the substrate for SERS. It was found that sensitivity of the nanoporous Ag film grown on the fluorophosphate glass is close to results of SERS obtained on island structures grown on silicate glasses.

Effect of impurities and disordering on the photoluminescence of crystals and glasses in the system Li2O - 7GeO2

The work is devoted to the study of photoluminescence spectra of weakly polar ferroelectric crystals Li2Ge7O15 and Li2O – 7GeO2 glasses. For all initial samples was observed the wide intensive luminescence band with maximum in the region of 525–550 nm. The spectral distribution of intensity and the position of the maximum of the band for a Li2Ge7O15 crystal depended on the excitation wavelength (λex=405 nm or 365nm were used). The spectral profile of the luminescence band was broadened in glass containing of 0.67% copper. The intensity of the luminescence band was decreased 6 times for glass doped with Cr3+ ions (0.01%) as compared with glass containing Cu2+ ions. The intense luminescence band of Cr3+ ions with λmax=659nm was appeared starting from 600. The assumption about the nature of the broad luminescence band observed in both nominally pure and doped glasses and crystals was made: the source of luminescence can be germanium - oxygen complexes [GeO4] and [GeO6] of the tetrahedral and octahedral configuration in the material structure.

In vitro monitoring of glutathione via a switched-on effect based on a lanthanide incorporated carbon nanostructure with biocompatibility

Selective determination of targets in live cells and the real-time detection of active species will be highly valuable in biological field. Integration of 3-hydroxybenzoic acid and europium ions under hydrothermal conditions would lead to the formation of regular carbon nanoparticles with the size of 10–20 nm. This novel nanostructure possessed striking blue luminescence and no effective lanthanide signals were detected. In the presence of glutathione (GSH), the europium incorporated nanoparticles showed intensive red luminescence and an “off-on” change was observed. It has been accepted that GSH acts as an antioxidant to protect cell via entrapping free radicals and it controls oxidative stress within living systems. The abnormal levels of GSH will be closely related to a variety of diseases. Therefore, the bio-distribution and in vitro detection of GSH were investigated in this study. The biocompatibility and cytotoxicity of the europium incorporated nanoparticles were also evaluated by MTT assay and flow cytometry. This new system will be essential to monitor the concentration of important biological compounds in living organisms.

Phenanthroline derivative based europium(III) covalently bonded silica hybrid material for high-selectivity sensing of anion and small organic molecule

A new polysilsesquioxane bridge (PhenOHSi) was synthesized here using 2-(2-hydroxyphenyl)-imidazo[4,5-f]-1,10-phenanthroline (PhenOH) and 3-(triethoxysilyl)propyl isocyanate respectively as a ligand of Eu3+ ion and a siloxane network precursor. Then, an organic–inorganic hybrid material covalently grafted with an Eu3+ complex (denoted as Eu(PhenOHSi)2Phen) was synthesized by coordination of an Eu3+ ion with a multifunctional precursor PhenOHSi and a second ligand Phen in a sol–gel process. This hybrid material was found to exhibit intensive red luminescence under UV light triggered by the ligand antenna effect. Further luminescent studies indicate that Eu(PhenOHSi)2Phen not only displays high sensitivity sensing targeted at fluoride ions, but also exhibits distinct solvent-dependent luminescent spectra with emission intensities that are significantly quenched by N,N-dimethylformamide.

Intensive luminescence from a thick, indium-rich In0.7Ga0.3N film

An In0.7Ga0.3N layer with a thickness of 300 nm deposited on GaN/sapphire template by molecular beam epitaxy has been investigated by highly spatially resolved cathodoluminescence (CL). High crystal film quality without phase separation has been achieved. The InGaN layer shows intense emission in the IR spectral region. The lateral as well as the vertical luminescence distribution is used to probe the In composition ([In]) homogeneity: the thick InGaN film exhibits laterally a rather homogeneous emission intensity at 1.04 eV (∼1185 nm) with a FWHM of only 63 meV. Carrier localization into regions of enhanced In concentration originating from compositional fluctuations is revealed. The evolution of emission in growth direction has been explored by a cross-sectional CL linescan showing a slight spectral redshift from the bottom to the surface of the InGaN film corresponding to an increase of [In] of only 0.5% within the layer thickness of 300 nm.

Investigation of Spectral Properties of Potassium Aluminoborate Glasses Doped with Chromium

Spectral properties of potassium aluminoborate glasses activated by various concentrations of trivalent chromium compounds are studied. The temperatures of glass transition (434°C) and bulk crystallization of the glass matrix (600°C) are determined. The heat treatment of the glass at the crystallization temperature results in the appearance of intensive narrow luminescence bands in the area of 685–715 nm that is connected with the crystallization of the LiAl7B4O17:Cr3+ phase in the glass matrix; in this phase chromium is located in a highly symmetrical octahedral surrounding. Concentration dependences of lifetime and quantum yield show the existence of the concentration luminescence quenching at increasing chromium content in the glass from 0.05 to 0.2 mol %. The maximum value of quantum yield is 30%.

THE SOURCES OF RADIATION IN THE SHORT-WAVE RANGE ON THE BASIS OF II-VI HETEROLAYERS

The possibility of obtaining zinc selenide and zinc sulfide layers of hexagonal modification by isovalent substitution method is shown. They are characterized by intensive luminescence which is formed by the dominant annihilation of bound excitons for α-ZnSe and recombination on donor-acceptor pairs for α-ZnS. The resulting radiation covers the violet wavelength range. Quantum radiation efficiency reaches η = 10–12% for α-ZnSe and η = 5–8% for α-ZnS. The radiation is characterized by high temperature stability and repeatability of characteristics and parameters.

Elaboration and characterization of glass–ceramic enriched by heavily manganese doped zinc silicate nanoparticles for optoelectronic applications

Nanocrystallines Mn2+-doped zinc silicate (β-Zn2SiO4:Mn) embedded in SiO2 host matrix were synthesized in two steps. In the first one a sol–gel process was used for the elaboration of silica aerogel monolith enriched by ZnO:Mn nanoparticles using supercritical conditions of ethanol. In the second step a simple solid-phase reaction under natural atmosphere at 1500 °C was investigated. The structure and texture of the obtained nanocomposites were studied by X-ray diffraction and transmission electron microscopy respectively. The optical results indicate that the obtained nanocomposites have excellent luminescence properties in the visible range. In addition, the PL spectrum for the β-Zn2SiO4:Mn/SiO2 nanocomposite reveals a band centered at about 584 nm attributed to the 4T1–6A1 transitions of Mn2+ ions. The intensive yellow luminescence presents a red shift and the lifetime is relatively weak compared to the known luminescence properties of this material. The obtained results are attributed to the protocol used and the excess of Mn2+ ions. The linear diminishing behaviours of the PL integrate intensity with the operating temperature, and the variation of the time decay with the Mn2+ contents; make it possible to anticipate the utilization of this material in luminescence thermometry.

Influence of Eu3+ concentration on photoluminescence and structure of Ba3Y1 − zEuz(BO3)3

A series of Ba3Y1 − zEuz(BO3)3 has been synthesized via a conventional solid state method. XRD, SEM, FL, EDS and lifetime decay curves were utilized for characterization. XRD and SEM confirmed that the phase of samples was transited from α-Ba3Y(BO3)3 to β-Ba3Eu(BO3)3 while Eu3+ concentration (z) increased from 0.20 to 0.40. The structure distortion due to different radius of Eu3+ and Y3+ and point defects due to the exchange of Eu3+ and Ba2+ ions were responsible for phase transition. In α phase, the R/O ratio of Eu3+ increased with z because of the point defects. On the other hand, R/O ratio stayed at around 1.080 in β phase. Second-order exponential decay curve of Ba3Y0.95Eu0.05(BO3)3 was a solid evidence for point defects in α phase. Excited at 394 nm, Ba3Y1 − zEuz(BO3)3 mainly showed intensive luminescence peaks at 596 and 616 nm ascribed to electron transitions 5D0→7F1 and 7F2, respectively. The obtained red phosphor is a great option for displays.

Infrared-to-visible upconversion luminescence in SrF2:Er powders upon excitation of the 4I13/2 level

Fluorite-type SrF2:Er powders were synthesized by using a co-precipitation from the aqueous solution technique. X-ray powder diffraction, scanning electron microscopy, absorption and luminescence spectroscopy were used to characterize the samples. For the first time upconversion luminescence of SrF2:Er powders in the visible and near-infrared spectral region upon excitation of 4I13/2 level Er3+ ions was investigated. The decrease in the slopes of the visible upconversion luminescence with increasing excitation power density and concentration of Er3+ ions were experimentally observed and discussed. The most intensive visible luminescence was obtained for SrF2:Er (8.8%) with a maximum quantum yield of 0.19%. Chromaticity coordinates and color temperature of yellow-green upconversion luminescence of SrF2:Er were calculated.

Mechanisms and absolute quantum yield of upconversion luminescence of fluoride phosphors

Mechanisms of upconversion luminescence (UCL) of SrF2:Er phosphors corresponding to the G411/2→I415/2, H29/2→I415/2, F45/2→I415/2, F47/2→I415/2, H211/2→I415/2, S43/2→I415/2, F49/2→I415/2, and I49/2→I415/2 transitions upon excitation of the I411/2 level of Er3+ ions were investigated. Energy transfer upconversion processes are responsible for the populating of the H29/2, H211/2, S43/2, and F49/2 levels. Cooperative process is the dominant mechanism of luminescence from S43/2 and F49/2 levels for SrF2:Er with high concentrations of Er3+ ions. The UCL from G411/2 and F45/2 is explained by excited-state absorption. Cross-relaxation processes take part in the population of F49/2 and I49/2 levels. For quantifying material performance, the Er3+-concentration dependence of UCL and the absolute quantum yields of SrF2:Er were studied. The most intensive visible luminescence was obtained for SrF2:Er (14.2%) with 0.28% maximum quantum yield.

Quantification of excitation-power dependency in Tm3 +/Yb3 + doped fluorotellurite upconverting glass phosphor for iris recognition

Excitation-power dependency of upconversion (UC) photons have been quantified in Tm3+/Yb3+ doped fluorotellurite (BALMT) glasses under the excitation of 975nm laser. The net powers of three-photon-excited blue and red and two-photon-excited NIR emissions are determined to be 242, 101 and 7994μW in 0.5wt% Tm2O3 and 2wt% Yb2O3 co-doping case under the excitation power of 870mW, respectively, and the net emission photon numbers are identified to be 58.2×1013, 33.0×1013 and 3253.2×1013cps. The quantum yields (QYs) for multi-photon-excited UC emissions of Tm3+ are identified as a positive dependency with pumping powers, and the relativity for three-photon fluorescence is extremely severe. When the excitation power density is set to 110.8W/mm2, the QY values for 476nm blue and 650nm red UC emissions are up to 1.49×10−4 and 0.84×10−4, and furthermore, the value for 809nm NIR UC emission is as high as 83.22×10−4. The 809nm luminescence is one of the good matching wavelengths for iris recognition in NIR ranges, the intensive NIR luminescence and the efficient blue fluorescence are promising in scanning and positioning for iris scanning. The macroscopic quantization for UC photon generation from Tm3+ in low-phonon fluorotellurite glasses provides a reliable reference for developing compact high-power-density light sources in iris recognition.

Triboluminescence and crystal structure of centrosymmetric complex Tb(AcAc)3Phen

The atomic structure of crystals of the complex Tb(AcAc)3Phen (AA –acetylacetonate-anion, Phen – 1,10 - phenanthroline) characterized by an intensive luminescence and triboluminescence has been determined by means of the X-ray structural analysis method. The crystal structure is represented by individual С27Н29N2O6Tb complexes linked through van der Waals interactions with clearly expressed cleavage planes. The structural aspects of the suggested model of formation of the triboluminescent properties have been considered and the role of the cleavage planes has been discussed. The notions of destruction zone and destruction zone width were introduced for the crystal under mechanical impact. This zone boundaries and width are naturally determined by surfaces spreading through central Tb atoms of molecular complexes, on which the ionization of charged acetylacetonate ions occurs as a result of the mechanical impact. In the case of the studied complex, the width of such destruction zone is equal to 6.414Å.

Coffee Grounds to Multifunctional Quantum Dots: Extreme Nanoenhancers of Polymer Biocomposites.

Central to the design and execution of nanocomposite strategies is the invention of polymer-affinitive and multifunctional nanoreinforcements amenable to economically viable processing. Here, a microwave-assisted approach enabled gram-scale fabrication of polymer-affinitive luminescent quantum dots (QDs) from spent coffee grounds. The ultrasmall dimensions (approaching 20 nm), coupled with richness of diverse oxygen functional groups, conferred the zero-dimensional QDs with proper exfoliation and uniform dispersion in poly(l-lactic acid) (PLLA) matrix. The unique optical properties of QDs were inherited by PLLA nanocomposites, giving intensive luminescence and high visible transparency, as well as nearly 100% UV-blocking ratio in the full-UV region at only 0.5 wt % QDs. The strong anchoring of PLLA chains at the nanoscale surfaces of QDs facilitated PLLA crystallization, which was accompanied by substantial improvements in thermomechanical and tensile properties. With 1 wt % QDs, for example, the storage modulus at 100 °C and tensile strength increased over 2500 and 69% compared to those of pure PLLA (4 and 57.3 MPa), respectively. The QD-enabled energy-dissipating and flexibility-imparting mechanisms upon tensile deformation, including the generation of numerous shear bands, crazing, and nanofibrillation, gave an unusual combination of elasticity and extensibility for PLLA nanocomposites. This paves the way to biowaste-derived nanodots with high affinity to polymer for elegant implementation of distinct light management and extreme nanoreinforcements in an ecofriendly manner.

Surface modified EuxLa1-xF3 nanoparticles as luminescent biomarkers: Still plenty of room at the bottom

Investigation of the formation and luminescent properties of surface modified bimetallic lanthanide fluorides and their use in bioimaging is described. We have shown that the solvent during the wet synthesis of EuF3 nanoparticles affects the nanoparticle morphology, which in turn influences the conditions of its phase transition from hexagonal to orthorhombic. The morphology of bimetallic EuxLa1-xF3 depends on the europium fraction x, allowing nanoparticles of ca. 50 nm to be obtained. Surface modification with aromatic carboxylates (L) allowed luminescence intensity increase by two orders magnitude, while luminescence quantum yield (PLQY) dependence on Eu fraction was shown to be affected by the ligand L: so, when L = 2,6-naphtalenedicarboxylate, PLQY reached its maximum of 70% at x = 0.3, while when L = terephthalate, almost no quantum yield decrease was observed for 0.01 < x < 0.3 (PLQY = 70 ± 5%). Nanoparticles solubilized in water were obtained by different polymer immobilization of the particle surface, and the use of poly(vinylpyrrolidone) (PVP) resulted in the formation of non-toxic nanoparticles PVP@L@Eu0.3La0.7F3, which uniformly distributed in cell cytoplasm and exhibited intensive luminescence in cells.

Construction of biodegradable and biocompatible AIE-active fluorescent polymeric nanoparticles by Ce(IV)/HNO3 redox polymerization in aqueous solution

Aggregation-induced emission (AIE) active fluorescence polymeric nanoparticles (FPNs) have recently received increasing interests for biomedical applications such as cell imaging, drug delivery, disease diagnosis and treatment. Fabricated strategies of AIE-active FPNs with high efficiency, simplification and tenderness are still passionately pursued to promote the development of theranostic systems. In this work, we develop a facile method for the preparation of AIE-active FPNs by adopting Ce(IV)/HNO3 redox polymerization under near room temperature. Thus-prepared FPNs (named as PEG-PLC-1) possess unique AIE feature, great water dispersity, excellent biocompatibility and biodegradability because of the conjugation of ultra-bright AIE dye (PhE-alc) and biodegradable PEG-PCL linear copolymers. The 1H nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), UV–Visible and fluorescence spectrometers were used to confirm the successful fabrication of AIE-active FPNs. Cell viability and cellular uptake behavior of PEG-PLC-1 FPNs were further investigated for their potential biomedical applications. Results demonstrated that PEG-PLC-1 FPNs are high water dispersity, intensive luminescence and low cytotoxicity, making them very attractive for biomedical applications. More importantly, the method for the fabrication of AIE-active biodegradable FPNs can be occurred under rather facile conditions (e.g., low temperature, free of metal catalysts, common chain transfer agent and aqueous solution) and are specially used for fabrication of AIE-active polysaccharides with poor organic solubility.

Nature of intensive defect-related broadband luminescence of heavily doped AlxGa1-xN:Si layers

We report photoluminescence investigations of heavily doped AlxGa1-xN:Si films grown by molecular beam epitaxy on sapphire substrates. The wide intensive defect-related band dominates in the photoluminescence spectra of AlxGa1-xN:Si films with the Al content higher than 0.46 covering the whole visible spectral range. This band is attributed to donor-acceptor transitions. The acceptor ionization energy of about 1.87 eV for heavily doped AlN:Si was obtained, decrease of Al content leads to decrease of the acceptor ionization energy. The donor was assigned to the Si atom on the Ga/Al site; the acceptor might be the (2-/3-) transition level of the VAl.