摘要 :
Gd_(2.97)Tb_(0.03)Ga_(5-x)Al_xO_(12) powders with different Ga:Al ratio were prepared using modifed Pechini method. Changing Ga:Al ratio opens the way to modulate the energy gap, and so, to modify the spectroscopic properties of t...
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Gd_(2.97)Tb_(0.03)Ga_(5-x)Al_xO_(12) powders with different Ga:Al ratio were prepared using modifed Pechini method. Changing Ga:Al ratio opens the way to modulate the energy gap, and so, to modify the spectroscopic properties of the phosphors. Al~(3+) ions stabilize the metastable Gd_3Ga_5O_(12) garnet structure widening the energy gap. With increasing Ga content in the garnet structure, the energy gap between an excited 5d level of Tb~(3+) ions and the conduction band (CB) decreases, which leads to an overlap of the conduction band with the 5d band suppressing the energy transfer between the 5d band and the 4f levels of Tb~(3+) ions. The band gap changes lead to the blue shift of charge transfer band due to an expansion of the unit cell and decreased interaction between oxygen ligands and luminescent ions. The collected spectroscopic data show signifcant effect of crystal feld strength of the host matrix on both conventional and persistent luminescence. From the resultant data the infuence of Ga:Al ratio on the luminescence properties and trapping/releasing of electrons is discussed. The mechanism of Tb~(3+) persistent luminescence in Gd_(2.97)Tb_(0.03)Ga_(5-x)Al_xO_(12) is proposed.
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Here, we report the facile synthesis of a highly ordered luminescent ZnO nanowire array using a low temperature anodic aluminium oxide (AAO) template route which can be economically produced in large scale quantity. The as-synthes...
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Here, we report the facile synthesis of a highly ordered luminescent ZnO nanowire array using a low temperature anodic aluminium oxide (AAO) template route which can be economically produced in large scale quantity. The as-synthesized nanowires have diameters ranging from 60 to 70 nm and length ～11 μm. The photoluminescence spectrum reveals that the AAO/ZnO assembly has a strong green emission peak at 490 nm upon excitation at a wavelength of 406 nm. Furthermore, the ZnO nanowire array-based gas sensor has been fabricated by a simple micromechanical technique and its NH3 gas sensing properties have been explored thoroughly. The fabricated gas sensor exhibits excellent sensitivity and fast response to NH_3 gas at room temperature. Moreover, for 50 ppm NH_3 concentration, the observed value of sensitivity is around 68%, while the response and recovery times are 28 and 29 seconds, respectively. The present synthesis technique to produce a highly ordered ZnO nanowire array and a fabricated gas sensor has great potential to push the low cost gas sensing nanotechnology.
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Photoluminescent phosphors CaGa2S4: EU2+, RE3+ (RE3+ including all rare earth ions except for Sc3+, pM(3+), Eu3+ and Lu3+) were prepared by sintering at high temperature in a reductive atmosphere, and their luminescent properties ...
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Photoluminescent phosphors CaGa2S4: EU2+, RE3+ (RE3+ including all rare earth ions except for Sc3+, pM(3+), Eu3+ and Lu3+) were prepared by sintering at high temperature in a reductive atmosphere, and their luminescent properties were studied intensively. The influences of co-doping rare earth ions on their luminescent properties were also investigated. No remarkable differences were found from excitation spectra of co-doped phosphors CaGa2S4: Eu2+, RE3+ in contrast with that of phosphor CaGa2S4: Eu2+, but there were a few differences in emission spectra of Cc(3+), Pr3+ or Ho3+ co-doped phosphors. Phosphors CaGa2S4: Eu2+, RE3+ (RE = Ce, Pr, Gd, Tb, Ho and Y) had persistent afterglow, and very short afterglow was shown for Nd3+ or Er3+ co-doped phosphors, but no long afterglow appeared when auxiliary activator was La3+, Sm3+, Dy3+, Tm3 + or Yb3+. Among the phosphors with long-lasting phosphorescence, in our experiments, CaGa2S4: Eu2+, Ho3+ had the longest and the highest brightness long yellow afterglow. Thermo-luminescence of all co-doped phosphors was measured to find the answer of different influences from different rare earth auxiliary activators.) (c) 2006 Elsevier Ltd. All rights reserved.
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ZnGa2S4: Eu2+ shows a light green emission at room as well as at low temperatures. The maximum of the band of the 4f(6)5d(1) -> 4f(7) emission is located at about 536 nm (18657 cm(-1)) and depends slightly on the excitation energy...
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ZnGa2S4: Eu2+ shows a light green emission at room as well as at low temperatures. The maximum of the band of the 4f(6)5d(1) -> 4f(7) emission is located at about 536 nm (18657 cm(-1)) and depends slightly on the excitation energy. The respective excitation band has a maximum at 470 nm (21277 cm(-1)). These results lead to the assumption that the Eu2+ ions are substituted at octahedral voids of the host lattice rather than at cationic sites. This is to be expected also because of the different ionic radii of the cations. Further emission and excitation bands are detected at higher energies in ZnGa2S4:Eu2+ as well as in undoped ZnGa2S4 which depend strongly on the respective excitation and emission energies and can, thus, be assigned to host lattice bands.
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A series of luminescent rare-earth ion-doped hexagonal II-rype Gd oxycarbonate phosphors Gd_(2-x)RE_xO2CO3 (RE = Eu~(3+), Yb~(3+), Dy~(3+)) have been successfully synthesized by thermal decomposition of the corresponding mixed oxa...
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A series of luminescent rare-earth ion-doped hexagonal II-rype Gd oxycarbonate phosphors Gd_(2-x)RE_xO2CO3 (RE = Eu~(3+), Yb~(3+), Dy~(3+)) have been successfully synthesized by thermal decomposition of the corresponding mixed oxalates. The Yb~(3+) doped Gd-oxycarbonate has evidenced a high persistent luminescence in the NIR region, that is independent from the temperature and makes this materials particular attractive as optical probes for bioimaging.
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Luminescence, mainly thermoluminescence (TL) and optically stimulated luminescence (OSL), has been researched for more than five decades towards its application to earth and planetary sciences. Luminescence production mechanism ha...
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Luminescence, mainly thermoluminescence (TL) and optically stimulated luminescence (OSL), has been researched for more than five decades towards its application to earth and planetary sciences. Luminescence production mechanism has been understood through several theoretical studies, like analytical kinetic theory, numerical models along with the experimental results. Instrument development has progressed with aim from user friendly TL/OSL reader dedicated for dating to challenging reader for in-situ Martian sediment dating. Since the development of optical dating in 1985, the technique revolutionised the research in earth sciences. And since then to recent, many methodologies have been developed and some are in developing stage using different signals, like, single grain OSL, red TL, time resolved OSL, thermally transferred OSL (TT-OSL), post infrared- infrared stimulated luminescence (pIR-IRSL), violet light stimulated luminescence (VSL), infrared radioluminescence (IRRL), etc. with an objective to improve the accuracy and precision and to extend the dating range. The wide range of application in different environment, e.g. aeolian, fluvial, marine, glacier, soil, volcanic materials, heated materials, shocked materials, meteorites, etc. have made the technique successful to understand the quaternary history of earth and planetary information like terrestrial and cosmic ray exposure ages of meteorite, meteoroid orbit, thermal metamorphism history of meteorite etc. The aim of this present paper is to discuss some landmarks and recent trends in the development and application in these areas.
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Herein, we investigate the performance of single- and multiparametric luminescence thermometry founded on the temperature-dependent spectral features of Ca6BaP4O17:Mn5+ near-infrared emission. The material was prepared by a conven...
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Herein, we investigate the performance of single- and multiparametric luminescence thermometry founded on the temperature-dependent spectral features of Ca6BaP4O17:Mn5+ near-infrared emission. The material was prepared by a conventional steady-state synthesis, and its photoluminescence emission was measured from 7500 to 10,000 cm?1 over the 293-373 K temperature range in 5 K increments. The spectra are composed of the emissions from 1E → 3A2 and 3T2 → 3A2 electronic transitions and Stokes and anti-Stokes vibronic sidebands at 320 cm?1 and 800 cm?1 from the maximum of 1E → 3A2 emission. Upon temperature increase, the 3T2 and Stokes bands gained in intensity while the maximum of 1E emission band is redshifted. We introduced the procedure for the linearization and feature scaling of input variables for linear multiparametric regression. Then, we experimentally determined accuracies and precisions of the luminescence thermometry based on luminescence intensity ratios between emissions from the 1E and 3T2 states, between Stokes and anti-Stokes emission sidebands, and at the 1E energy maximum. The multiparametric luminescence thermometry involving the same spectral features showed similar performance, comparable to the best single-parameter thermometry.
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When activated by Dy~(3+), Na_(0.25)K_(0.25)Bi_(0.50)TiO_3 (NKBT), piezoelectric powders show strong luminescence in the blue and yellow spectral range. Emissions of this material can be effectively utilized for both luminescence ...
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When activated by Dy~(3+), Na_(0.25)K_(0.25)Bi_(0.50)TiO_3 (NKBT), piezoelectric powders show strong luminescence in the blue and yellow spectral range. Emissions of this material can be effectively utilized for both luminescence intensity ratio and lifetime-based readouts of temperature. Photoluminescence measurements over a temperature range of 293-483 K show that the luminescence intensity ratio temperature readout has maximal relative sensitivity of 1.93% K~(-1) at 380 K, while the relative sensitivity of the lifetime temperature readout reaches 1.1% K~(-1) at 480 K. For this study, materials were synthesized by a solid-state reaction using TiO_2, Bi_2O_3, Na_2CO_3, K_2CO_3 and Dy_2O_3 as precursors. X-ray diffraction measurements showed that the NKBT sample crystallized in the A-site substituted distorted perovskite rhombohedral structure (R3c symmetry). The photoluminescence spectra showed characteristic emission bands of Dy~(3+) ions centered at 457 nm (~4I_(15/2) → ~6H_(15/2)), 478 nm (~4F_(9/2) → ~6H_(15/2)), 574 nm (~4F_(9/2) → ~6H_(13/2)) and 663 nm (~4F_(9/2) → ~6H_(11/2)). The ratio of emissions from ~4F_(9/2) and ~4I_(15/2) excited states to the ~6H_(15/2) ground state was used as a luminescence intensity ratio indicator of temperature, while the decay of emission from ~4F_(9/2) → ~6H_(13/2) transition was used as a lifetime indicator of temperature. CIE coordinates x = 0.326 and y = 0.361 calculated from room temperature emission spectra show the perspective of this material for use in white light emission devices.
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The development of luminescent materials for anticounterfeiting and encryption is of great importance. Herein, we develop a multistimuli-responsive luminescent material, Na2CaGe2O6:Pb2+/Er3+, and use it to print luminescent images...
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The development of luminescent materials for anticounterfeiting and encryption is of great importance. Herein, we develop a multistimuli-responsive luminescent material, Na2CaGe2O6:Pb2+/Er3+, and use it to print luminescent images. The photoluminescence and upconversion luminescence of these images show different patterns and colors under different stimuli. The photostimulated luminescence (PSL) of the printed images causes dynamic changes in appearance and is accordingly applied for dynamic multi modal anticounterfeiting on banknotes. The PSL of these luminescent images is also applied in a virtual war scenario to demonstrate that the dynamic PSL-encrypted information in the fabricated image is sufficiently safe even in extreme cases and that spies will be detected. These results can inspire us with more creative security designs based on this luminescent material.
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In the paper, after a brief description of historical development, the theory of thermoluminescence (TL) is presented. Three methods of thermally (TSL), optically (OSL) and radio (RPL) stimulated luminescence are discussed and com...
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In the paper, after a brief description of historical development, the theory of thermoluminescence (TL) is presented. Three methods of thermally (TSL), optically (OSL) and radio (RPL) stimulated luminescence are discussed and compared. A wide range of applications of TL detectors in individual and environmental dosimetry with an attention put on ultra-high dose measurements is presented and described. As particularly important in clinical dosimetry for eye-tumor radiotherapy, the surface 2D detectors were developed. The participation of the Institute of Nuclear Physics (IFJ) group in the Cosmos experiment MATROSHKA is described. Also, the new TL materials and measurement methods are presented.
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