Pr Absorption Research Articles

Effects of static magnetic field, driving laser strength and polarization on the coherent properties of a microwave mediated four-level tripod-type atomic system

In this theoretical work, we study the optical behaviour of a microwave driven four-level tripod-type atomic system, configured by Zeeman sub-levels in D 1 line of 87 Rb atom. The non-optical microwave field (L) reasonably assists the optical pumping by a linearly polarized (π) laser field (P1) and a right-handed circularly polarized (σ +) laser field (P2), in presence as well as absence of a static magnetic field (MF). The optical responses of the system to the left-handed circularly polarized (σ −) optical probe laser field (Pr) under three specific P1-P2 strength conditions depict substantial variations in the Doppler-free and Doppler-broadened absorption peaks, accompanied with single EIT or double EIT windows. The origin of Doppler-free Pr absorption peaks are explained by analyzing the resonant poles for the scanning Pr which attribute to the decaying-dressed-states. Perceptible changes of resonant pole positions on the complex planes of the poles w. r. t. the applied MF and L signify that one can externally alter the optical responses of the medium. The related Pr dispersion and its controllability are discussed as well. It is found that the interaction length of the Doppler-free medium has a prominent effect on the Pr absorption and transmission when both MF and L are present in the medium. Furthermore, we have shown the modifications in the Doppler-free Pr absorption profiles in presence of MF and L by considering P2 as an elliptically polarized laser field. Interestingly, Pr absorption turns into Pr gain at suitable polarization rotation angles of the elliptically polarized P2 field for different P1-P2 strength ratios.

Structure and luminescence investigation of Gd3+-sensitized perovskite CaLa4Ti4O15:Eu3+: A novel red-emitting phosphor for high-performance white light-emitting diodes and plants lighting

A novel perovskite CaLa4Ti4O15:Eu3+ red-emitting phosphor was synthesized via a sol-combustion method, and Gd3+ was further co-doped into structure to improve the luminescence performance. The effects of Eu3+ doping and Gd3+ co-doping concentrations on the microstructure and luminescence properties were investigated. The red emission peaks of as-prepared phosphors originate from the 5D0→7Fj electron transitions of Eu3+ ions. Under 273 nm excitation, the luminescence intensity of Eu3+ was significantly enhanced through the energy transfer between Gd3+ and Eu3+ in CaLa4Ti4O15, and the luminescence intensity was also improved even under the excitation of 394 nm. By combining red-emitting CaLa4Ti4O15:Eu3+, Gd3+ phosphor with commercial blue and green phosphors on n-UV chip (λ = 395 nm), an eye-friendly w-LEDs with appropriate correlated color temperature (4761 K) and high color rendering index (Ra = 93.1) has been realized. The electroluminescence spectrum of the packaged red LED have an excellent match with the PR absorption of plants. In addition, when introducing CaLa4Ti4O15:Eu3+, Gd3+ phosphor into a commercial w-LED with YAG:Ce3+, the adjustable chromaticity parameters like CCT and CRI values can be obtained. These results demonstrated that the as-prepared CaLa4Ti4O15:Eu3+, Gd3+ phosphor is an outstanding candidate as the red component for the application of w-LEDs and plants lighting.

Differing biophysical properties underpin the unique signaling potentials within the plant phytochrome photoreceptor families

Many aspects of photoperception by plants and microorganisms are initiated by the phytochrome (Phy) family of photoreceptors that detect light through interconversion between red light- (Pr) and far-red light-absorbing (Pfr) states. Plants synthesize a small family of Phy isoforms (PhyA to PhyE) that collectively regulate photomorphogenesis and temperature perception through redundant and unique actions. While the selective roles of these isoforms have been partially attributed to their differing abundances, expression patterns, affinities for downstream partners, and turnover rates, we show here from analysis of recombinant Arabidopsis chromoproteins that the Phy isoforms also display distinct biophysical properties. Included are a hypsochromic shift in the Pr absorption for PhyC and varying rates of Pfr to Pr thermal reversion, part of which can be attributed to the core photosensory module in each. Most strikingly, PhyB combines strong temperature dependence of thermal reversion with an order-of-magnitude faster rate to likely serve as the main physiological thermosensor, whereby thermal reversion competes with photoconversion. In addition, comparisons of Pfr occupancies for PhyA and PhyB under a range of red- and white-light fluence rates imply that low-light environments are effectively sensed by PhyA, while high-light environments, such as full sun, are effectively sensed by PhyB. Parallel analyses of the Phy isoforms from potato and maize showed that the unique features within the Arabidopsis family are conserved, thus indicating that the distinct biophysical properties among plant Phy isoforms emerged early in Phy evolution, likely to enable full interrogation of their light and temperature environments.

A novel Sm3+-activated Li3BaSrLn3(MO4)8 [Ln = La, Gd, and Y; M = Mo and W] deep red-emitting phosphors for plant cultivation and white LEDs

Deep red phosphor-based LEDs play a crucial role in plant growth applications, where the LED emission covers the phytochrome (Pr) absorption. In this context, a series of Sm3+-activated Li3BaSrLn3(MO4)8:Sm3+ [Ln = La Gd and Y; M = Mo and W] deep red phosphors were synthesized using the solid-state method. The outcome of the PXRD patterns suggests that the synthesized phosphors were crystallized in a monoclinic structure with the space group C2/c. SEM analysis was executed to study the morphology of the phosphors, and an FT-IR study was performed to study the stretching frequency of the MO/W-O bond in the (Mo/W)O4 groups. All the Sm3+-activated phosphors showed intense emission at 646 nm due to their 4G5/2→6H9/2 transition and exhibited excellent thermal stability (> 72% at 423K). The selected phosphors showed internal quantum efficiency at around 30%. The pc-LEDs were fabricated with the combination of near-UV LED and the synthesized deep-red phosphors. Besides, the emission spectrum of the fabricated LED was compared with the phytochrome Pr absorption spectrum for de plant growth application. These results suggest that the synthesized phosphor can be useful in the white LED fabrication to improve the CRI and can also be beneficial in the plant growth field.

Electronic transitions and heterogeneity of the bacteriophytochrome Pr absorption band: An angle balanced polarization resolved femtosecond VIS pump–IR probe study

Photoisomerization of biliverdin (BV) chromophore triggers the photoresponse in native Agp1 bacteriophytochrome. We discuss heterogeneity in phytochrome Pr form to account for the shape of the absorption profile. We investigated different regions of the absorption profile by angle balanced polarization resolved femtosecond VIS pump–IR probe spectroscopy. We studied the Pr form of Agp1 with its natural chromophore and with a sterically locked 18Et-BV (locked Agp1). We followed the dynamics and orientations of the carbonyl stretching vibrations of ring D and ring A in their ground and electronically excited states. Photoisomerization of ring D is reflected by strong signals of the ring D carbonyl vibration. In contrast, orientational data on ring A show no rotation of ring A upon photoexcitation. Orientational data allow excluding a ZZZasa geometry and corroborates a nontwisted ZZZssa geometry of the chromophore. We found no proof for heterogeneity but identified a new, to our knowledge, electronic transition in the absorption profile at 644 nm (S0→S2). Excitation of the S0→S2 transition will introduce a more complex photodynamics compared with S0→S1 transition. Our approach provides fundamental information on disentanglement of absorption profiles, identification of chromophore structures, and determination of molecular groups involved in the photoisomerization process of photoreceptors.

A bacteriophytochrome regulates the synthesis of LH4 complexesin Rhodopseudomonas palustris

The non-sulphur purple bacterium Rhodopseudomonas palustris contains five pucAB genes for peripheral light-harvesting complexes. Bacteria grown under high-light conditions absorb at 800 and 850 nm but in low-light the 850 nm peak is almost absent and LH2 complexes are replaced by LH4. The genome contains six bacteriophytochromes (Bph). Bphs sense light in the red/far-red through a reversible Pr to Pfr transformation that controls gene expression. Bph3 (RPA1537) controls the expression of a cluster of photosynthetic genes, however most of the peripheral light harvesting complex genes are outside of this region. The pucAB-d genes encode LH4 peptides and are near two Bphs (RPA3015, RPA3016). We have characterised three Bphs and show that Bph4 RPA3015 and Bph3 RPA1537 have different dark stable states. It is known that Bph3 is active in its red absorbing Pr form and suggests a working hypothesis that Bph4 is active in the Pfr state. We show that LH4 expression can be induced with red light at the Pr absorption maximum (708 nm) of Bph4. The property of light transmission of water maybe an important factor in understanding this adaptation. Bph4 can sense the reduction in light intensity indirectly through an increase in ratio of transmitted red/far-red light. The red right activated Bph4 regulates the synthesis of LH4 which concentrates bacteriochlorophyll a pigment absorption at 800 nm to exploit a recovery in water light transmission in this region.

Synthesis and characterization of praseodymium-doped ceria powders by a microwave-assisted hydrothermal (MH) route

Nanocrystalline Pr-doped ceria powders were prepared for the first time by a microwave-assisted hydrothermal route. The effect of the microwave treatment in relation to the conventional hydrothermal technique was evaluated. The samples prepared were characterized in terms of composition, crystalline structure, particle shape and size distribution by X-ray diffraction, transmission electron microscopy (TEM) and specific surface area analysis (BET). The color properties of these solid solutions were also evaluated as a function of synthesis conditions and composition. Finally the oxidation state of the Pr cations and the relative quantities of Pr(IV) and Pr(III) were investigated by X-ray absorption at the M4,5 Pr absorption edge.

Effects of calcium concentration, acetate, and propionate on calcium absorption in the human distal colon

Previous studies have shown that the short-chain fatty acids acetate (Ac) and propionate (Pr) enhance the absorption of calcium (Ca) in the rectum and distal colon of humans, with Pr being more effective than Ac. To investigate the effect of Ac and Pr on the kinetics of Ca absorption from the human rectum and distal colon, six healthy subjects were studied. Solutions containing various concentrations of CaCl 2 · H 2O with 56.3 mmol/L Ac, Pr, or NaCl were rectally infused to each subject. Rectal fluid was sampled at the end of the infusion (0 min), and 30 min later colonic contents were collected. Ca absorption for all treatments increased linearly with Ca concentration. For Ca + NaCl, the slope of regression line was 62 μmol · mmol −1 · L Ca. With Ac + Ca, the slope of Ca absorption increased significantly to 113 μmol · mmol −1 · L Ca, and with Pr + Ca, the slope increased to 159 μmol · mmol −1 · L ( P = 0.043 versus Ac + Ca). Ac and Pr absorption were increased by Ca. The data suggest that, over a physiologic range of Ca concentration, in the absence or presence of Ac and Pr, Ca is absorbed in the human rectum and distal colon by a non-saturable diffusion process, and that Ca absorption is enhanced by Ac and Pr. The data also suggest that both Ac and Pr absorption is stimulated by Ca.

Resonant valence-to-core x-ray fluorescence spectroscopy on

The results of x-ray fluorescence measurements, performed with monochromatic-photon excitation at Pr absorption edges of , are presented and discussed in the framework of an Anderson impurity model. The dependence of the fluorescence structures on varying excitation energies is found to be in agreement with the localized, many-body description of the fluorescence process. Experimental spectra are reproduced by model calculations using values for the model parameters in the ground state of the system which are somewhat different from those obtained earlier in an analysis of core-level photoemission and absorption. Referring to this difference, the importance of resonant x-ray fluorescence data for the spectroscopic analysis of strongly correlated systems and for deriving a unique set of model parameters is stressed.

Comparison of photoacoustic spectroscopy, conventional absorption spectroscopy, and potentiometry as probes of lanthanide speciation

The authors measured the stability constants of praseodymium acetate and oxydiacetate complexes by laser-induced photoacoustic spectroscopy, conventional UV-visible absorption spectroscopy, and pH titration. For the spectroscopic studies, changes in the free Pr absorption peaks at 468 and 481 nm were monitored at varying ligand concentrations. The total Pr concentration was 1 {times} 10{sup {minus}4} M in solutions used for the photoacoustic studies and 0.02 M for conventional spectroscopy. For the pH titrations, we used solutions whose Pr concentrations varied from 5 {times} 10{sup {minus}3} to 5 {times} 10{sup {minus}2} M, with total ligand-to-metal ratios ranging from 1 to 10. A comparison of the results obtained by the three techniques demonstrates that photoacoustic spectroscopy can give the same information about metal-ligand speciation as more conventional methods. It is particularly suited to those situations where the other techniques are insensitive because of limited metal concentrations.

Modifications of Sulfhydryl Groups on Phytochrome and Their Influence on Physicochemical Differences between the Red- and Far-Red-Absorbing Forms

Phytochrome extracted from shoots of dark-grown rye (Secale cereale cv Rymin) and oat (Avena sativa cv Garry) as the far-red-form (Pfr) and/or under conditions conducive to oxidation exhibited a blue shift in the visible absorption maximum of its red-light-absorbing form (Pr) relative to that measured in vivo. This spectral alteration could not be reversed but could be prevented by inclusion of 10 millimolar diethyldithiocarbamate and 140 millimolar 2-mercaptoethanol in homogenization buffers. Similar blue shifts were induced in purified rye phytochrome by addition of the sulfhydryl-modifying reagent, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB). In spectrally normal phytochrome (i.e., no detectable blue shift), Pfr had three to four more sulfhydryls available for rapid reaction with DTNB than did Pr. This difference was maintained over a 2.5-hour time course. Phytochrome purified under conditions resulting in a blue-shifted Pr absorption maximum exhibited a decreased short-term reactivity of Pfr to DTNB. Comparison of the binding and elution of altered and unaltered phytochrome from agarose-immobilized Cibacron blue 3GA confirmed that the Pfr form of spectrally normal phytochrome had a greater affinity for the dye than did the Pr form but that spectral alteration of phytochrome was accompanied by a loss of this difference as evidenced by an increased binding of Pr to the dye. It was concluded that phytochrome has highly reactive sulfhydryl residues located on the portion of the protein that undergoes conformational changes on interconversion of Pr and Pfr and that these residues require rigorous protection in order to extract the native form of the protein from plant tissue.

Single mode magneto-optic waveguide films

A novel triple layer film is described which provides single mode propagation in a magneto-optically active waveguide of convenient thickness. All three layers are modified yttrium iron garnet (YIG) films grown by liquid phase epitaxy on a gadolinium gallium garnet substrate. The top film is the active layer, several microns thick. The middle layer is similar but it has a slightly smaller refractive index to assure single mode operation of the top layer. The bottom layer has high optical absorption to eliminate all of the higher order modes which are propagated in the triple layer and a slightly higher refractive index to prevent the confinement of any modes to the top two low loss layers. Using a praseodymium YIG film as the absorbing layer, 17 TE modes were propagated at 1.51 μm where the Pr absorption is low but only the TE0 mode was observed at 1.48 and 1.54 μm where the Pr absorption is high. Such triple layer garnet films will be useful in all magneto-optic waveguide devices.

Phytochrome-controlled extension growth of Avena sativa L. seedlings

Fluence rate response curves for light-induced inhibition of mesocotyl growth and promotion of coleoptile growth in etiolated Avena sativa L. (cv. Victory) were developed. The irradiation time was 24 h. Fluence rates between 10(-6) and 10(5) nmol m(-2)s(-1) and 30 wavelengths between 563 and 1,093 nm were used. The main conclusions are as follows: 1. Both organs exhibit a low fluence rate response as well as a high fluence rate response. 2. The mesocotyl response is more sensitive to light than the coleoptile response. 3. The low fluence rate response of the mesocotyl shows a threshold of sensitivity at about 10(-7) nmol m(-2)s(-1) (i.e., total fluence of 5·10(-2) nmol m(-2) during the experiment) in the red and a saturation (about 70% inhibition of growth) at 10(-4) nmol m(-2)s(-1) (50 nmol m(-2)). 4. The action spectrum for the low fluence rate response parallels the Pr absorption spectrum. Alterations induced by screening are discussed. 5. The action spectrum demonstrates an exponential decrease in apparent photoconversion cross-section (Pr→Pfr) up to about 800 nm. Between 800 and 1,093 nm the photoconversion cross-section is only weakly dependent on wavelength. 6. The action spectrum for the high fluence rate response shows a broad peak in the red, a trough at 723 nm, and a sharp peak at 740-750 nm.