scholarly journals Temperature Effects in Rhodamine B Dyes and Improvement in CW Dye Laser Performance

1991 ◽  
Vol 11 (1) ◽  
pp. 31-38 ◽  
Author(s):  
M. A. Ali ◽  
J. Moghaddasi ◽  
S. A. Ahmed
Keyword(s):  
Rhodamine B ◽  
Room Temperature ◽  
Argon Laser ◽  
Dye Laser ◽  
Laser Medium ◽  
Quantum Yields ◽  
Threshold Power ◽  
Relaxation Processes ◽  
Negative Effects ◽  
Intermolecular Relaxation

The effect of cooling the laser medium on the lasing characteristics of an organic cw dye laser, Rhodamine B in ethylene glycol, pumped by an Argon laser was examined. Significant improvements in the performance of this dye laser were achieved as the solvent temperature was reduced below room temperature, namely: a significant reduction in the threshold power requirements and a considerable increase in the attainable output power. The results obtained may be understood in terms of increased quantum yield of the RhB dye as the temperature is reduced. This effect overrides possible negative effects that are normally expected due to intermolecular relaxation processes and which are normally observed for other dye lasers which already have high quantum yields at room temperature.

scholarly journals The behaviour of visual purple at low temperature

1941 ◽  
Vol 179 (977) ◽  
pp. 151-159 ◽  
Keyword(s):  
Aqueous Solution ◽  
Low Temperature ◽  
Low Temperatures ◽  
Room Temperature ◽  
Absorption Curve ◽  
Quantum Yields

Visual purple is soluble and stable in a mixture of glycerol and water (3:1). At room temperature the spectrum of such a solution is identical with that of the aqueous solution. At — 73° C the peak of the absorption curve is higher and narrower than at room temperature, and it is shifted towards longer waves. The product of photodecomposition at — 73° C has a spectrum in ­ dependent of pH and is at low temperatures thermostable and photostable, but at room temperature it decomposes therm ally to indicator yellow. The primary product appears to be identical with transient orange. The quantum yields of the photoreaction at low and at room temperature are of the same order.

Alteration of argon laser–induced scars by the pulsed dye laser

1993 ◽  
Vol 13 (3) ◽  
pp. 368-373 ◽  
Author(s):  
Tina S. Alster ◽  
Amal K. Kurban ◽  
Gary L. Grove ◽  
Mary J. Grove ◽  
Oon Tian Tan
Keyword(s):  
Argon Laser ◽  
Dye Laser ◽  
Pulsed Dye Laser

Structural and electrical properties of KCa2Nb5O15 ceramics

Open Physics ◽  
2008 ◽  
Vol 6 (2) ◽  
Author(s):  
Banarji Behera ◽  
Pratibindhya Nayak ◽  
Ram Choudhary
Keyword(s):  
Electrical Properties ◽  
Temperature Variation ◽  
Electrical Transport ◽  
Room Temperature ◽  
Complex Impedance ◽  
Tungsten Bronze ◽  
Transport Processes ◽  
Relaxation Processes ◽  
Orthorhombic Crystal Structure ◽  
Grain Distribution

AbstractA polycrystalline sample of KCa2Nb5O15 with tungsten bronze structure was prepared by a mixed oxide method at high temperature. A preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound shows a uniform grain distribution throughout the surface of the sample. Studies of temperature variation on dielectric response at various frequencies show that the compound has a transition temperature well above the room temperature (i.e., 105°C), which was confirmed by the polarization measurement. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (31–500°C) and frequency (102–106 Hz) range that showed only bulk contribution and non-Debye type relaxation processes in the material. The activation energy of the compound (calculated from both the loss and modulus spectrum) is same, and hence the relaxation process may be attributed to the same type of charge carriers. A possible ‘hopping’ mechanism for electrical transport processes in the system is evident from the modulus analysis. A plot of dc conductivity (bulk) with temperature variation demonstrates that the compound exhibits Arrhenius type of electrical conductivity.

scholarly journals Regioisomeric Effect on the Excited-State Fate Leading to Room-Temperature Phosphorescence or Thermally Activated Delayed Fluorescence in a Dibenzophenazine-Cored Donor–Acceptor–Donor System

2021 ◽  
Author(s):  
Takumi Hosono ◽  
Nicolas Oliveira Decarli ◽  
Paola Zimmermann Crocomo ◽  
Tsuyoshi Goya ◽  
Leonardo Evaristo de Sousa ◽  
...  
Keyword(s):  
Excited State ◽  
Room Temperature ◽  
Delayed Fluorescence ◽  
Quantum Yields ◽  
Room Temperature Phosphorescence ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Donor Acceptor ◽  
Emission Behavior

Exploring design principle for switching thermally activated dealyed fluorescecne (TADF) and room temperature phosphorescence (RTP) is a fundamentally imporant research in developing triplet-mediated photofunctional organic materials. Herein systematic studies on the regioisomeric and substituents effects in a twisted donor–acceptor–donor (D–A–D) scaffold (A = dibenzo[a,j]phenazine; D = dihydrophenazasiline) on the fate of the excited state have been performed. The study revealed that the regiosiomerism clearly affects the emission behavior of the D–A–D compounds. Distinct difference in TADF, dual TADF & RTP, and dual RTP were observed, depending on the host used. Furthermore, OLED organic light-emitting diodes (OLEDs) fabricated with the developed emitters achieved high external quantum yields for RTP-based OLEDS up to 7.4%.

Reactions of Thiyl Radicals. XI. Further Investigations of Thiol–Disulfide Photolyses in the Liquid Phase

1973 ◽  
Vol 51 (9) ◽  
pp. 1410-1415 ◽  
Author(s):  
Donna D. Carlson ◽  
Arthur R. Knight
Keyword(s):  
Liquid Phase ◽  
Room Temperature ◽  
Liquid Mixtures ◽  
Quantum Yields ◽  
Chain Reaction ◽  
Photochemical Process ◽  
High Quantum Efficiency ◽  
Thiyl Radicals ◽  
Exchange Processes ◽  
A Chain

The photolysis of C2H5SH liquid at 2537 Å has been shown to give H2 and C2H5SSC2H5 at equal rates with a quantum yield of 0.25. The photolysis of ethanethiol – methyl disulfide liquid mixtures leads, via a chain reaction involving propagation by attack of thiyl radicals on the disulfide S—S bond, to the formation with high quantum efficiency of CH3SH, C2H5SSC2H5 and, as an intermediate that is consumed after long exposures, CH3SSC2H5. The net result of the sequence of exchange processes is the essentially irreversible conversion of the methyl disulfide into methanethiol. The same overall reaction occurs thermally at room temperature, but the rate is appreciably less than that of the photochemical process. The quantum yields of formation of the unsymmetrical disulfides arising from the photochemically initiated exchange reaction in equimolar mixtures of CH3SSCH3 + n-C3H7SSC3H7 and C2H5SSC2H5 + n-C3H7SSC3H7 have been shown to be 6.9 and 4.4, compared to 355 for CH3-SSCH3 + C2H5SSC2H5 mixtures. In all three types of system examined in this investigation all thiyl radicals can be accounted for stoichiometrically on the basis of exchange and combination reactions alone, indicating negligible disproportionation of these species in condensed phase.

Vitrimer enhanced carbazole-based organic room-temperature phosphorescent materials

2021 ◽  
Author(s):  
Tianqi Xu ◽  
Peng Wu ◽  
Lingyun Lou ◽  
Yuzhan Li ◽  
Dong Wang ◽  
...  
Keyword(s):  
Room Temperature ◽  
Radiative Transition ◽  
Quantum Yields

Organic room-temperature phosphorescent(RTP) materials have promising applications, but due to the lack of inter-system scaling and susceptibility to non-radiative transition, they typically have low quantum yields (<2%) and short lifetimes...

Phytofluors: Phytochrome-Based Orange Fluorescent Protein Probes

1999 ◽  
Vol 5 (S2) ◽  
pp. 1050-1051
Author(s):  
J. Clark Lagarias ◽  
Beronda L. Montgomery ◽  
John T. Murphy ◽  
Shu-Hsing Wu
Keyword(s):  
Room Temperature ◽  
Fluorescent Protein ◽  
Protein Complexes ◽  
Quantum Yields ◽  
Color Intensity ◽  
Photosynthetic Organisms ◽  
Orange Fluorescent Protein ◽  
Pigment Protein Complexes ◽  
Covalently Linked ◽  
Light Color

Plants sense the light environment using pigment-protein complexes that discriminate light color, intensity, duration and direction. The most well-studied of these photoreceptors are the phytochromes, a family of soluble biliproteins found in plants, algae and cyanobacteria. Owing to the linear tetrapyrrole pigment phytochromobilin (PΦB) or phycocyanobilin (PCB) that is covalently linked to a large polypeptide via a thioether linkage, phytochromes perceive differences in the quality and quantity of light via their ability to photointerconvert between red (λmax660 nm) and far-red (λmax730 nm) light absorbing forms. Due to an efficient Z,E photoisomerization of the double bond between the C and D-ring pyrroles, phytochromes are nonfluorescent proteins with fluorescent quantum yields less than 10“3 at room temperature (Figure 1).Phytochrome genes have been cloned from a wide variety of photosynthetic organisms.

Photochemische 2+2-Cycloadditionen von Äthylen und Acetylen an 1.3-Cyclohexadien unter erhöhtem Druck / Photochemical 2+2-Cycloadditions of Ethylene and Acetylene to 1,3-Cyclohexadiene under High Pressure

1977 ◽  
Vol 32 (1) ◽  
pp. 47-52 ◽  
Author(s):  
Marlis F. Mirbach ◽  
Manfred J. Mirbach ◽  
Alfons Saus
Keyword(s):  
High Pressure ◽  
Quantum Yield ◽  
Room Temperature ◽  
Kinetic Scheme ◽  
Solvent Mixture ◽  
Experimental Results ◽  
Quantum Yields ◽  
Ethylene Pressure ◽  
Formal Kinetic

The photochemical cycloaddition of 1,3-cyclohexadiene (CHD) to ethylene and acetylene at pressures above 10 bar is described. Upon sensitized irradiation (2-acetylnaphthaline) CHD adds to ethylene at room temperature in dichloromethane to give cis-bicyclo[4,2,0]-oct-2-ene (1) along with dimers of cyclohexadiene. The yield of cross adduct increases with ethylene pressure (10-50 bar) whereas dimerisation decreases. Quantum yields of cross addition and dimerisation at 12 M ethylene were determined to be 0.31 and 0.35 respectively. At a pressure of 15 bar acetylene CHD reacts with acetylene to give bicyclo-[4,2,0]octa-2,7-diene (2) and bicyclo[2,2,2]octa-2,5-diene (3) as the major and minor products respectively. In a solvent mixture containing 60 vol-% CH2Cl2 and 40 vol-% acetone (2) is formed with a quantum yield of φ = 0.2. The experimental results are explained by a formal kinetic scheme.

scholarly journals Interaction of zinc and IAA alleviate aluminum-induced damage on photosystems via promoting proton motive force and reducing proton gradient in alfalfa

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Liantai Su ◽  
Jianping Xie ◽  
Wuwu Wen ◽  
Jiaojiao Li ◽  
Peng Zhou ◽  
...  
Keyword(s):  
Energy Production ◽  
Foliar Spray ◽  
Quantum Yields ◽  
Zn Deficiency ◽  
Negative Effects ◽  
Transfer Rates ◽  
Apical Buds ◽  
Zn Addition ◽  
Photosynthetic Machinery ◽  
Al Treatment

Abstract Background In acidic soils, aluminum (Al) competing with Zn results in Zn deficiency in plants. Zn is essential for auxin biosynthesis. Zn-mediated alleviation of Al toxicity has been rarely studied, the mechanism of Zn alleviation on Al-induced photoinhibition in photosystems remains unclear. The objective of this study was to investigate the effects of Zn and IAA on photosystems of Al-stressed alfalfa. Alfalfa seedlings with or without apical buds were exposed to 0 or100 μM AlCl3 combined with 0 or 50 μM ZnCl2, and then foliar spray with water or 6 mg L− 1 IAA. Results Our results showed that Al stress significantly decreased plant growth rate, net photosynthetic rate (Pn), quantum yields and electron transfer rates of PSI and PSII. Exogenous application of Zn and IAA significantly alleviated the Al-induced negative effects on photosynthetic machinery, and an interaction of Zn and IAA played an important role in the alleviative effects. After removing apical buds of Al-stressed alfalfa seedlings, the values of pmf, gH+ and Y(II) under exogenous spraying IAA were significantly higher, and ΔpHpmf was significantly lower in Zn addition than Al treatment alone, but the changes did not occur under none spraying IAA. The interaction of Zn and IAA directly increased Y(I), Y(II), ETRI and ETRII, and decreased O2− content of Al-stressed seedlings. In addition, the transcriptome analysis showed that fourteen functionally noted genes classified into functional category of energy production and conversion were differentially expressed in leaves of alfalfa seedlings with and without apical buds. Conclusion Our results suggest that the interaction of zinc and IAA alleviate aluminum-induced damage on photosystems via increasing pmf and decreasing ΔpHpmf between lumen and stroma.

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