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1.
Poly(rI) stabilized by either Na+ or K+ was investigated using uv resonance Raman (UVRR) spectroscopy. Raman excitation profiles of inosine 5′-monophosphate demonstrated the 250 nm excitation selectively enhances base stacking interactions, while ribose and carbonyl stretching vibrations are preferentially enhanced with 210 nm excitation. These wavelengths were used to examine the structure of poly(rI) in the presence of either K+ or Na+ as a function of temperature. UVRR studies revealed that the K+ stabilized form is more thermally stable, yielding a Tm of ∼ 47°C compared to a Tm of ∼ 30°C for the Na+ stabilized form. We observed that both the ribosyl conformation and the coordination of the carbonyl groups depend on the nature of the cation. The C6O stretching frequency indicates that Na+ coordinates much more strongly to the carbonyl groups than K+ (1672 cm−1 Na+ vs 1684 cm−1 K+ at 4°C). Conformationally sensitive modes of the phosphate backbone and the ribosyl ring indicate that Na+ stabilized poly(rI) predominantly exists in a C3′-endo ribose conformation, whereas K+ stabilized poly(rI) adopts a C2′-endo conformation possibly as a consequence of the larger ionic radius of the K+ ion. © 1998 John Wiley & Sons, Inc. Biopoly 46: 475–487, 1998 相似文献
2.
The temporal characteristics of the slow phase of chlorophyll fluorescence induction-T 0.5 (half-decay time) and t min (an integral-based index of the variable emission rate)-as well as the popular amplitude index F P/F S were determined at different excitation light intensities (I ex [400?C500 nm] of 20?C80 W/m2) in dark-adapted leaves of different age (3?C24 days) taken from radish plants grown under continuous light of 100 W/m2 PAR. All the profiles thus obtained were mutually consistent, and the age-related variations were minimized at I ex > 40 W/m2; at that the age-averaged temporal indices proved to be more light-responsive than the standard amplitude ratio. 相似文献
3.
Polycrystalline Sr2SnO4 phosphors doped with Tb3+ were prepared by conventional solid‐state reaction method. Materials were characterized by powder XRD and EDS techniques. The luminescence properties of these materials were investigated under UV and VUV excitation. Upon excitation at 272 nm, phosphors exhibited intense emissions at 492 and 543 nm due to 5D4 → 7 F6 and 5D4 → 7 F5 transitions of Tb3+ ions, respectively. Materials also exhibited strong emissions from these transitions under VUV excitation at 147, 173 and 230 nm. Quantitative analysis of the spectra indicated probable applications of these phosphors for PDP and other display devices as green emitting phosphors. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
Effect of preillumination on the P-680+ reduction kinetics in chloride-free photosystem II membranes
《FEBS letters》1986,203(2):215-219
The re-reduction course of P-680+, the photooxidized PS II primary donor, was measured as a function of excitation number in Cl−-depleted PS II membranes. After the 1st and 2nd excitations the signal amplitude of P-680+ is small, indicating a submicrosecond reduction of P-680+ by Z, the secondary donor of PS II. After the 3rd excitation, however, a larger P-680+ signal with a 40–50 μs half-life is observed. The slow decay of this signal is attributed to a back-reaction with a reduced acceptor in the presence of the Z+S2 state on the donor side. The state Z+S2 has a lifetime longer than 300 ms and its formation was found to depend on the presence of the abnormal S2 state created by the 1st excitation. The P-680 data and thermoluminescence measurements show that the S-state advancement beyond S2 is blocked in the absence of Cl− and that the Cl−-free abnormal S2 state has a lifetime about 10-times longer than the normal S2 state. 相似文献
5.
A series of Eu2+ activated SrCaP2O7 pyrophosphate phosphors were synthesized by the modified solid‐state reaction method. The X‐ray diffraction (XRD) and photoluminescence (PL) properties of these phosphors were investigated at room temperature. The excitation spectra indicate that these phosphors can be effectively excited by Hg‐free excitation. The emission spectra exhibit strong blue performance, which is due to the 4f65d1→4f7 transition of Eu2+. The Fourier transform infrared spectrum at room temperature was investigated and surface morphology has been studied by scanning electron microscope. The prepared phosphor exhibited intense blue emission at the 427 nm owing to Eu2+ ion by Hg‐free excitation at 330 nm, that is, solid‐state lighting excitation. Hence, the availability of such a phosphor will significantly help in the growth of blue‐emitting solid‐state lighting applications. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
6.
A series of efficient Li3Al2(PO4)3:Eu2+ novel phosphors were synthesized by the facile combustion method. The effects of dopant on the luminescence behavior of Li3Al2(PO4)3 phosphor were also investigated. The phosphors were characterized by X‐ray diffraction, field emission scanning electron microscope and photoluminescence techniques. The result shows that all samples can be excited efficiently by near‐ultraviolet excitation under 310 nm. The emission was observed for Li3Al2(PO4)3:Eu2+ phosphor at 425 nm, which corresponded to the d → f transition. The concentration quenching of Eu2+ was observed in Li3Al2(PO4)3:Eu2+ when the Eu concentration was at 0.5 mol%. The prepared powders exhibited intense blue emission at the 425 nm owing to the Eu2+ ion by Hg‐free excitation at 310 nm (i.e., solid‐state lighting excitation). Consequently, the availability of such a phosphor will significantly help in the development of blue‐emitting solid‐state lighting applications. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
7.
A solid‐state reaction route‐based LiTi2 ? xEux(PO4)3 was phosphor synthesized for the first time to evaluate its luminescence performance by excitation, emission and lifetime (τ) measurements. The LiTi2 ? xEux(PO4)3 phosphor was excited at λexci. = 397 nm to give an intense orange–red (597 nm) emission attributed to the 5D0 → 7F1 magnetic dipole (ΔJ = ±1) transition and red (616 nm) emission (5D0 → 7F2), which is an electric dipole (ΔJ = ±2) transition of the Eu3+ ion. Beside this, excitation and emission spectra of host LiTi2(PO4)3 powder were also reported. The effect of Eu3+ concentration on luminescence characteristics was explained from emission and lifetime profiles. Concentration quenching in the LiTi2 ? xEux(PO4)3 phosphor was studied from the Dexter's model. Dipole–quadrupole interaction is found to be responsible for energy transfer among Eu3+ ions in the host lattice. The LiTi2 ? xEux(PO4)3 phosphor displayed a reddish‐orange colour realized from a CIE chromaticity diagram. We therefore suggest that this new phosphor could be used as an optical material of technological importance in the field of display devices. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
8.
White‐ and blue‐light‐emitting dysprosium(III) and terbium(III)‐doped gadolinium titanate phosphors
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Here we report the synthesis and structural, morphological, and photoluminescence analysis of white‐ and blue‐light‐emitting Dy3+‐ and Tm3+‐doped Gd2Ti2O7 nanophosphors. Single‐phase cubic Gd2Ti2O7 nanopowders consist of compact, dense aggregates of nanoparticles with an average size of ~25 nm for Dy3+‐doped and ~50 nm for Tm3+‐doped samples. The photoluminescence results indicated that ultraviolet (UV) light excitation of the Dy3+‐doped sample resulted in direct generation of white light, while a dominant yellow emission was obtained under blue‐light excitation. Intense blue light was obtained for Tm3+‐doped Gd2Ti2O7 under UV excitation suggesting that this material could be used as a blue phosphor. 相似文献
9.
《Journal of receptor and signal transduction research》2013,33(1-4):493-507
AbstractReceptor-mediated alterations in the cytosolic free calcium concentration, [Ca2+]i are monitored with the intracellular fluorescent calcium probe fura 2 by dual excitation microfluori-metry. The calcium dependence on the excitation spectrum of fura 2 allows us to choose two wavelengths, λ1 and λ2, at which an increase in [Ca2+]i causes either a rise or a fall in fluorescence; the ratio of fluorescence at λ1 and λ2 (R =Fλ1/Fλ2) is a measure of [Ca2+]i. It appears essential for such measurements that the alteration between the two excitation wavelengths is done rapidly, to allow us to distinguish between effects on [Ca2+]i and other effects on fluorescence. In addition, specific problems relating to the calibration of fura 2 measurements, such as its relative insensitivity at basal [Ca2+]i, the role of intracellular viscosity on fura 2 fluorescence, and the difficulties encountered in establishing calibration constants have to be appreciated. In spite of these potential drawbacks, it appears that monitoring receptor-mediated [Ca2+]i regulation in single cells will prove essential for the further comprehension of stimulus-secretion coupling in pituitary and probably many other cell types. 相似文献
10.
LaBSiO5 phosphors doped with Ce3+ and Tb3+ were synthesized using the conventional solid‐state method at 1100 °C. The phase purity and luminescent properties of these phosphors are investigated. LaBSiO5:Tb3+ phosphors show intense green emission, and LaBSiO5 phosphors doped with Ce3+ show blue–violet emission under UV light excitation. LaBSiO5 phosphors co‐doped with Ce3+ and Tb3+ exhibit blue–violet and green emission under excitation by UV light. The blue–violet emission is due to the 5d–4f transition of Ce3+ and the green emission is ascribed to the 5D4 → 7 F5 transition of Tb3+. The spectral overlap between the excitation band of Tb3+ and the emission band of Ce3+ supports the occurrence of energy transfer from Ce3+ to Tb3+, and the energy transfer process was investigated. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
11.
Pore water nutrient profiles and dynamics in soft bottoms of the northern Baltic Sea 总被引:1,自引:0,他引:1
Chemical profiles of nutrients at the sediment–water interface were measured in the northern Baltic Sea. A whole core squeezer technique capable of mm-scale resolution was used to obtain the vertical profiles of NO3
–, NO2
–, o-P, NH4
+ and Si in the soft bottom sediments. The profiles were compared with nutrient flux and denitrification measurements. In the Gulf of Finland, the profiles revealed a marked chemical zonation in NO3
– and NO2
– distribution indicating strong potential of nitrification just under the sediment surface followed by a layer of denitrification down to a depth of 30 mm. Below the depth of 20 mm NO3
– was usually absent, whereas other nutrients were increasing steadily in concentration. A distinct minimum of NO3
– was observed at the sediment–water interface, suggesting NO3
– uptake by a microbial biofilm and/or active denitrification at the suboxic microniches usually present in organic-rich sediments. At the deep stations in the Baltic Proper, the NO3
– concentration in pore water, as well as denitrification, were very low. The concentrations of NH4
+, o-P and Si were usually increasing steadily with depth. 相似文献
12.
Sushant Rajendra Bargat Yatish Ratn Parauha Nayana Sudhakar Shirbhate Girish Mishra Sanjay Janaraoji Dhoble 《Luminescence》2022,37(3):463-471
In the recent few years, Eu2+- and Mn4+-activated phosphors are widely used as potential colour converters for indoor plant cultivation lighting application due to their marvellous luminescence characteristics as well as low cost. In this investigation, we synthesized novel red colour-emitting Ca(2−x)Mg2(SO4)3:xmol% Eu2+ (x = 0–1.0 mol%) phosphors via a solid-state reaction method in a reducing atmosphere. The photoluminescence (PL) excitation spectra of synthesized phosphors exhibited a broad excitation band with three excitation bands peaking at 349 nm, 494 nm, and 554 nm. Under these excitations, emission spectra exhibited a broad band in the red colour region at ~634 nm. The PL emission intensity was measured for different concentrations of Eu2+. The maximum Eu2+ doping concentration in the Ca2Mg2(SO4)3 host was observed for 0.5 mol%. According to Dexter theory, it was determined that dipole–dipole interaction was responsible for the concentration quenching. The luminous red colour emission of the sample was confirmed using Commission international de l'eclairage colour coordinates. The results of PL excitation and emission spectra of the prepared phosphors were well matched with excitation and emission wavelengths of phytochrome PR. Therefore, from the entire investigation and obtained results it was concluded that the synthesized Ca0.995Mg2(SO4)3:0.5mol%Eu2+ phosphor has huge potential for plant cultivation application. 相似文献
13.
Yu‐Guo Yang Xu‐Ping Wang Bing Liu Yuan‐Yuan Zhang Xian‐Shun Lv Jing Li Lei Wei Hua‐Jian Yu Yanyan Hu Hua‐Di Zhang 《Luminescence》2020,35(4):580-585
Dy3+‐doped Y3Al5O12 phosphors were prepared at a relatively low temperature using molten salt synthesis. The phase of the prepared Dy3+‐doped Y3Al5O12 phosphors was confirmed using X‐ray powder diffraction. Results indicated that Dy3+ doping did not change the Y3Al5O12 phase. Following excitation at 352 nm, emission spectra of the Dy3+‐doped Y3Al5O12 phosphors consisted of blue, yellow, and red emission bands. The influence of Dy3+ concentration and excitation wavelength on emission was investigated. The ratio of yellow light to blue light varied with change in Dy3+ doping concentration, due to changes in the structure around Dy3+. Emission intensities also changed when the excitation wavelength was changed. This variation is luminescence generated a system for tunable white light for Dy3+‐doped Y3Al5O12 phosphors. 相似文献
14.
A series of praseodymium (Pr3+) ion activated Sr3Gd(1−x)(PO4)3:xPr3+ (0 ≤ x ≤ 2.0 mol%) phosphors were prepared and their structural, compositional and luminescence properties were investigated. The X-ray diffraction profiles indicate that the studied phosphors crystallized into body centred cubic structure and the Pr3+ ions have no influence on Sr3Gd(PO4)3 phase. The high-resolution scanning electron microscopy images show the agglomeration of particles that are inter-connected and form irregular shape Sr3Gd(PO4)3 structures. The excitation transitions corresponding to Pr3+:3H4 → 3P2,1,0 transitions at 445, 471 and 483 nm, respectively, matched well with the emission of blue-light-emitting diode (LED) chip. The emission spectra show strong reddish-orange luminescence through 1D2 → 3H4 transition when excited at 445 nm blue wavelength. The synthesized phosphors have the potential to be used as reddish-orange lighting devices. 相似文献
15.
Viji Vidyadharan E. Sreeja Saritha K. Jose Cyriac Joseph N. V. Unnikrishnan P. R. Biju 《Luminescence》2016,31(1):202-209
The spectroscopic and photoluminescence characteristics of trivalent dysprosium (Dy3+)‐doped Sr0.5Ca0.5TiO3 phosphor materials synthesized via solid‐state reaction method were studied. The X‐ray diffraction profile confirmed the orthorhombic perovskite structure of the prepared samples. Judd–Ofelt analysis was carried out to obtain the intensity parameters and predicted radiative properties of Sr0.5Ca0.5TiO3:2wt%Dy3+. The photoluminescence spectrum of Dy3+‐doped Sr0.5Ca0.5TiO3 showed three emission peaks at 481, 574 and 638 nm corresponding to 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2 transitions respectively. The variation of luminescence intensity with different excitation wavelengths and Dy3+ concentrations is discussed. The decay profiles of 4F9/2 excited levels of Dy3+ ions show bi‐exponential behaviour and also a decrease in average lifetime with increase in Dy3+ concentration. Yellow to blue luminescence intensity ratio, CIE chromaticity co‐ordinates and correlated color temperature were also calculated for different concentrations of Dy3+‐doped Sr0.5Ca0.5TiO3 phosphor at different λex. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
16.
KLaSiO4:Tb3+ phosphors were synthesized using the sol–gel method. The structure and luminescence properties of the materials were characterized using X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, thermogravimetry–differential thermal analysis, fluorescence spectra and calculated Commission Internationale de l'éclairage coordinates. The results showed that the material had a hexagonal structure, and that doping of Tb3+ did not change the crystal structure of KLaSiO4. FTIR spectroscopy confirmed the existence of stretching vibrations of Si–O, bending vibrations of Si–O–Si, and asymmetric tensile vibrations of Si–O in KLaSiO4. The excitation spectrum of the sample consisted of 4f7→5d1 broadband absorption and the characteristic excitation peak of Tb3+, the excitation peak at 232 nm belongs to the spin allowed 7FJ→7DJ transition of Tb3+, the excitation peak at 268 nm belongs to the spin forbidden 7FJ→9DJ transition of Tb3+, and the absorption band of 7FJ→7DJ transition is split. Under excitation at 232 nm, the emission peak of the sample was composed of the 5D4→7FJ (J = 6, 5, 4, 3) energy level transition of Tb3+. The highest emission peak is located at 543 nm, which belongs to the 5D4→7F5 transition and emits green light. Concentration quenching occurred when the Tb3+ doping concentration was greater than 1% mol, the quenching mechanism was an electric dipole–electric dipole action. When the ratio of citric acid to total metal ions was 1:1 and the annealing temperature was 800°C, the surface defects of the phosphors were greatly reduced, the quenching effect was reduced, and the luminous intensity reached the maximum. 相似文献
17.
In this article we report Eu3+ luminescence in novel K3Ca2(SO4)3Cl phosphors prepared by wet chemical methods. The Eu3+ emission was observed at 594 nm and 615 nm, keeping the excitation wavelength constant at 396 nm nearer to light‐emitting diode excitation, Furthermore, phosphors were characterized by X‐ray diffraction for the confirmation of crystallinity. The variation of the photoluminescence intensity with impurity concentration has also been discussed. Thus, prominent emission in the red region makes prepared phosphors more applicable for white light‐emitting diodes. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
18.
Eu3+‐activated Y(P,V)O4 phosphors were prepared by the EDTA sol‐gel method, and the corresponding morphologies and luminescent properties were investigated. The sample particles were relatively spheroid with size of 2–3 µm and had a smooth surface. The excitation spectra for Y(P,V)O4:Eu3+ consisted of three strong excitation bands in the 200–350 nm range, which were attributed to a Eu3+‐ O2? charge‐transfer band and 1A1?1 T1/1 T2 transitions in VO43?. The as‐synthesized phosphors exhibited a highly efficient red luminescence at 613 nm due to the Eu3+ 5D0?7 F2 electric dipole transition. With the increase in the V5+/P5+ ratio, the luminescence intensity of the red phosphor under UV excitation was greatly improved due to enhanced VO43? → Eu3+ energy transfer. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
19.
A green chemical precipitation route was used to yield a hydrated basic sulfate precursor upon calcination at 1000°C into a series of (Y,Gd)2O2SO4:Dy particles. The phosphors exhibited characteristic Dy3+ emissions from 4F9/2→6HJ (J = 15/2, 13/2, 11/2) transitions under ultraviolet light excitation; the quenching concentration of Dy3+ was determined to be 2.5 at.%. Substitution of Gd3+ for Y3+ led to an additional strong sharp band at ~277 nm (8S7/2→6IJ transition of Gd3+) in the photoluminescence excitation spectra, upon which the (Gd0.975Dy0.025)2O2SO4 phosphor achieved a ~2.8-fold higher photoluminescence intensity via an effective energy transfer from Gd3+ to Dy3+ compared with the 354 nm excitation of Dy3+. Both the photoluminescence and photoluminescence excitation intensities of (Y,Gd)2O2SO4:Dy phosphors increased with rising Gd3+ concentration and calcination temperature in the range 750–1000°C. A higher Gd3+ concentration slightly prolonged the effective fluorescence lifetime. 相似文献
20.
The photoexcited triplet states of bacteriochlorophyll a, 3BChl a, and of the primary donor in reaction centers of Rhodobacter sphaeroides R-26, 3P865, are investigated by pulsed EPR and ENDOR spectroscopy. In 3P865 a splitting of ENDOR lines and reduction of corresponding positive and negative hyperfine couplings as compared with the monomeric 3BChl a is observed. This indicates an asymmetric distribution of the triplet excitation over the two BChl a moieties, PL and PM, forming 3P865. Based on the signs of the hyperfine couplings and on a comparison with the cation and anion radical of BChl a an assignment to nuclei in the different dimer halves is proposed. This yields an estimate for the extent of delocalization of the triplet excitation over PL and PM and for the charge transfer contribution of 3P865. 相似文献