DOCSLIB.ORG

University Microfilms, Inc., Ann Arbor, Michigan PAST SPECTKOPHOSEHÜRIMETER

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
University Microfilms, Inc., Ann Arbor, Michigan PAST SPECTKOPHOSEHÜRIMETER MASTER'S THESIS M-642 HECKER, Irwin. FAST SPECTROPHOSPHORIMETER. The American University, M.S., 1963 Physics, general University Microfilms, Inc., Ann Arbor, Michigan PAST SPECTKOPHOSEHÜRIMETER Irwin Hecker Submitted to the Faculty of the College of Arts and Sciences of the American University in Partial Fulfillment of the Requirements for the Degree of Master of Science Signatures of Committee )eair o e College Date : Date; /^i3 A:izmcm umversit 1^55 LIBRARY The American University SEP 3 01964 Washington, D .G. WASHINGTON. D £ i:) ACKNOWLED GEMENTS I wish to thank the faculty and fellow students of the American University Physics Department for their stimulating discussions and suggestions during the development of the phosphorimeter, Dennis Robin­ son, an undergraduate research assistant at the univer­ sity, was very helpful in the construction and testing of the phosphorimeter. I am particularly indebted to Professorial Lecturer Samuel Moss for his direction and valuable criticisms. This research was sponsored by the American Instrument Go. Inc. of Silver Spring, Md. Finally, I wish to thank my wife, Barbara Hecker, for typing all of the manuscripts and for help with the proofs. CONTENTS LIST OF ILLUSTRATIONS........................ 1 1. INTRODUCTION............................. 2 1.1 Phosphorescence.................. 2 1.2 Present Phosphorimeters........... 4 1.5 Need For Fast Phosphorimeter...... 5 2. GENERAL DESCRIPTION..................... 7 2.1 Design Of System................... 7 2.2 System Operation................... 7 3. LIGHT SOURCE SUBSYSTEM.................. 10 5.1 Function Of Light Source........... 10 5.2 Explanation Of Circuit............. 10 4. PHOTOMULTIPLIER DETECTION SUBSYSTEM 16 4.1 Requirements On Detection Subsystem........................ 16 4.2 Theory Of Photomultiplier Tubes,... 16 4.3 Explanation Of Circuit............. 17 5. SWITCH SUBSYSTEM......................... 25 5.1 Timing ....................... 25 5.2 Delay Line........... 25 5.5 Monostable Multivibrator And Amplifier........................ 25 5.4 Shockley 4-Layer Diodes............ 27 5.5 High-Speed Switch.................. 50 6. CONCLUSION............................... 55 BIBLIOGRAHIY................................. 34 ILLUSTRATIONS 1. Block Diagram Of System.................. 8 2. Flash Tube Firing Circuit................ 11 3. Exciting Light Source Subsystem Schematic......... 12 4. Successive Light Pulse From Plash Source..... «................... 14 5. Gate Pulse Caused By Flash............... 14 6. Picture Of Flash Light Source.,.......... 15 7. Operation Of Secondary-Emission Multiplier Tubes....................... 17 8. Schematic Of Photomultiplier Detection System................................. 19 9. Voltage Across Phototube ........... 21 10. Pictures Of Detection System Components............. 22 11. Timing................................... 24 12. Delay Line, Multivibrator And Amplifier................. 26 1 3 . Characteristic V-1 Curve Of Shockley Diodes................................. 28 14. Construction Of Shockley Diode........... 28 1 5 . Picture Of Shockley Diode String......... 32 INTRODUCTION 1.1 PHOSPHORESCENCE When a substance absorbs energy a fraction of the absorbed energy may be re-emitted as electromagnetic radiation in the visible or near visible region of the spectrum. This phenomenon is called luminescence^. Luminescence involves at least two steps: the exci­ tation of the electronic system of the sample and the subsequent emission of photons. The initial excita­ tion may be caused by light, electron or ion bombard­ ment, mechanical strain, chemical reaction, or direct heating. Fluorescence is luminescence in which the light is emitted during excitation. Luminescence in which the light emission occurs after the excitation has ceased is referred to as phosphorescence or afterglow. The afterglow period may be from microseconds to hours in duration. A decay time of 10"^ seconds is frequent­ ly taken as the demarcation line between fluorescence and phosphorescence. This period is the approximate p lifetime for dipole radiation from an excited atom. 1 This term does not include the emission of block-body radiation, which obeys the laws of Kirchbbff and Wien. 2 Adrianus J. Dekker, Solid State Physics. (Englewood Cliffs, N.J., Prentice-Hall, Inc., 1961). Luminescent solids are usually referred to as phos­ phors . Several models have been successfully applied to the study of phosphorescence. The property of lu­ minescence is known to be due to the presence of small amounts of impurities, called activators, in the com­ pound. The phosphor chemists have been able to syn­ thesize, under carefully controlled conditions, much A. more efficient phosphors than those found in nature^. Photoluminescent phosphors are substances which absorb electromagnetic energy, usually ultraviolet light, subsequently re-emitting this energy in the form of visible light. The specific properties of a phosphor (e.g., the color of the light it emits, the wavelength of light it must absorb to be excited to fluorescence, the brightness of the emitted light, the duration of the phosphorescence, or afterglow) are a function of the physical nature of the material and the activator it contains. The decay characteristics of a phosphorescence substance are of great importance in the study of luminescence. According to the models, fluorescence and phosphorescence are both first-order 3 J.S. Prener, D.B. Sullenger, "Phosphors", Scientific American, (Oct. 1954). processes and follow exponential laws of decay. The identification of the luminescence centers and their energy levels is simplified if the decay characteris­ tics are knownt 1 .2 PRESENT PÏÏÜSPHÜRIMETERS Some important types of apparatus designed for investigation of photoluminescence are the phosphori- meters (phosphoroscopes) and fluorimeters. These serve for measuring the duration of short decaying e- mission process. These instruments are based on the principle of permitting the observation of the phos­ phorescence for a short, and if desired, a variable time after the end of the excitation-^. Although there is a wealth of equipment now avai­ lable for measurement of decay times, there is a need for a phosphoroscope v/hich is accurate, inexpensive, flexible, and capable of measuring decay times as short as 1 microsecond. Most phosphoroscopes now avai­ lable are limited by the speed of their mechanical components^. These instruments cannot measure decay 4 Dekker, op. cit. 5 For a detailed history and description of these devi­ ces see Peter Pringsheim, Fluorescence and Phospho­ rescence , (Interscience Idblishers, Inc., N.Y., 1949) ■ times of less than 10~^ seconds. For the measurement of shorter decay periods (down to 10 ^ seconds) fluo- rimeters are used. These devices are not limited in speed but have other disadvantages 7 . For example, fluorimeters which make use of Kerr cells have the li­ mitation that Kerr cells absorb certain wavelengths of light. Other fluorimeters require the incident light beam to be diffracted periodically by means of supersonic waves. These "supersonic-cell" 8 fluorime­ ters are very space consuming. Both types of fluo­ rimeters mentioned above are difficult to operate and expensive. 1.3 NEED FOR FAST PHOSPHORIMETER To more fully understand the structure a lumines­ cent compound, it is desirable to measure precisely the decay of both the fluorescence and the phosphores­ cence radiation. Since the fluorescence decay time for some substances is as long as 1 0 ”^ seconds, a fast, accurate phosphorimeter is required to be able to dis­ tinguish the phosphorescence radiation from the radia­ tion of fluorescence. 6 Such as the rotating discs used by Becquerel or the revolving mirrors used by Vavilov and Levshin. Ibid. 7 Ibid. 8 Ibid. Phosphors are widely used in fluorescent lamps, cathode ray oscilloscopes, radar and television pre­ sentation, and nucleon and radiation detectors. Better understanding of the nature of phosphors may lead to improvements of these devices. In addition, phosphorimeters have been applied to a number of problems involving both identification and quantita­ tive assay of many organic compounds. It was felt that it is within the state of the art to build a phosphoroscope which could measure decay times as short as lO"^ seconds and which would be inexpensive, easily operated, flexible, and accu­ rate. This device was designed to be used in conjunc­ tion with a system of two grating monochromators^ for selecting excitation and phosphorescence wave­ lengths. This paper describes the design and opera­ tion of the electronically switched phosphoroscope which resulted. 9 Such as the Aminco-Keirs Spectrophosphorimeter described in Instruction Book No. 816. (American Instrument Co. Inc., Silver Spring, Md., I960). 2 GENERAL DESCRIPTION 2.1 DESIGN OP SYSTEM The system can be logically divided into three subsystems: a source of light to excite the sample, an electronic switch to handle the delicate timing problem, and a unit which detects the phosphorescent radiation of the sample. Pig. 1 is a block design of the general features of the system. The exciting light source (A) was a Xenon flash tube. This tube produced a flash of high intensity and short dura­ tion. The electronic switch (B) was designed to switch very high voltages on to a load in less than one microsecond. The detection system (C) was de­ signed so that it could be sensitized a short time after sample excitation. 2.2 SYSTEM OPERATION The system functioned in the following manner:
Load more

Recommended publications
  • Glossary Physics (I-Introduction)
    1 Glossary Physics (I-introduction) - Efficiency: The percent of the work put into a machine that is converted into useful work output; = work done / energy used [-]. = eta In machines: The work output of any machine cannot exceed the work input (<=100%); in an ideal machine, where no energy is transformed into heat: work(input) = work(output), =100%. Energy: The property of a system that enables it to do work. Conservation o. E.: Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes. Equilibrium: The state of an object when not acted upon by a net force or net torque; an object in equilibrium may be at rest or moving at uniform velocity - not accelerating. Mechanical E.: The state of an object or system of objects for which any impressed forces cancels to zero and no acceleration occurs. Dynamic E.: Object is moving without experiencing acceleration. Static E.: Object is at rest.F Force: The influence that can cause an object to be accelerated or retarded; is always in the direction of the net force, hence a vector quantity; the four elementary forces are: Electromagnetic F.: Is an attraction or repulsion G, gravit. const.6.672E-11[Nm2/kg2] between electric charges: d, distance [m] 2 2 2 2 F = 1/(40) (q1q2/d ) [(CC/m )(Nm /C )] = [N] m,M, mass [kg] Gravitational F.: Is a mutual attraction between all masses: q, charge [As] [C] 2 2 2 2 F = GmM/d [Nm /kg kg 1/m ] = [N] 0, dielectric constant Strong F.: (nuclear force) Acts within the nuclei of atoms: 8.854E-12 [C2/Nm2] [F/m] 2 2 2 2 2 F = 1/(40) (e /d ) [(CC/m )(Nm /C )] = [N] , 3.14 [-] Weak F.: Manifests itself in special reactions among elementary e, 1.60210 E-19 [As] [C] particles, such as the reaction that occur in radioactive decay.
    [Show full text]
  • PHYSICS Glossary
    Glossary High School Level PHYSICS Glossary English/Haitian TRANSLATION OF PHYSICS TERMS BASED ON THE COURSEWORK FOR REGENTS EXAMINATIONS IN PHYSICS WORD-FOR-WORD GLOSSARIES ARE USED FOR INSTRUCTION AND TESTING ACCOMMODATIONS FOR ELL/LEP STUDENTS THE STATE EDUCATION DEPARTMENT / THE UNIVERSITY OF THE STATE OF NEW YORK, ALBANY, NY 12234 NYS Language RBERN | English - Haitian PHYSICS Glossary | 2016 1 This Glossary belongs to (Student’s Name) High School / Class / Year __________________________________________________________ __________________________________________________________ __________________________________________________________ NYS Language RBERN | English - Haitian PHYSICS Glossary | 2016 2 Physics Glossary High School Level English / Haitian English Haitian A A aberration aberasyon ability kapasite absence absans absolute scale echèl absoli absolute zero zewo absoli absorption absòpsyon absorption spectrum espèk absòpsyon accelerate akselere acceleration akselerasyon acceleration of gravity akselerasyon pezantè accentuate aksantye, mete aksan sou accompany akonpaye accomplish akonpli, reyalize accordance akòdans, konkòdans account jistifye, eksplike accumulate akimile accuracy egzatitid accurate egzat, presi, fidèl achieve akonpli, reyalize acoustics akoustik action aksyon activity aktivite actual reyèl, vre addition adisyon adhesive adezif adjacent adjasan advantage avantaj NYS Language RBERN | English - Haitian PHYSICS Glossary | 2016 3 English Haitian aerodynamics ayewodinamik air pollution polisyon lè air resistance
    [Show full text]
  • Introduction 1
    1 1 Introduction . ex arte calcinati, et illuminato aeri [ . properly calcinated, and illuminated seu solis radiis, seu fl ammae either by sunlight or fl ames, they conceive fulgoribus expositi, lucem inde sine light from themselves without heat; . ] calore concipiunt in sese; . Licetus, 1640 (about the Bologna stone) 1.1 What Is Luminescence? The word luminescence, which comes from the Latin (lumen = light) was fi rst introduced as luminescenz by the physicist and science historian Eilhardt Wiede- mann in 1888, to describe “ all those phenomena of light which are not solely conditioned by the rise in temperature,” as opposed to incandescence. Lumines- cence is often considered as cold light whereas incandescence is hot light. Luminescence is more precisely defi ned as follows: spontaneous emission of radia- tion from an electronically excited species or from a vibrationally excited species not in thermal equilibrium with its environment. 1) The various types of lumines- cence are classifi ed according to the mode of excitation (see Table 1.1 ). Luminescent compounds can be of very different kinds: • Organic compounds : aromatic hydrocarbons (naphthalene, anthracene, phenan- threne, pyrene, perylene, porphyrins, phtalocyanins, etc.) and derivatives, dyes (fl uorescein, rhodamines, coumarins, oxazines), polyenes, diphenylpolyenes, some amino acids (tryptophan, tyrosine, phenylalanine), etc. + 3 + 3 + • Inorganic compounds : uranyl ion (UO 2 ), lanthanide ions (e.g., Eu , Tb ), doped glasses (e.g., with Nd, Mn, Ce, Sn, Cu, Ag), crystals (ZnS, CdS, ZnSe, CdSe, 3 + GaS, GaP, Al 2 O3 /Cr (ruby)), semiconductor nanocrystals (e.g., CdSe), metal clusters, carbon nanotubes and some fullerenes, etc. 1) Braslavsky , S. et al . ( 2007 ) Glossary of terms used in photochemistry , Pure Appl.
    [Show full text]
  • Download Neon Lesson Plan (.Pdf)
    EXPLORING NEON At a Glance TARGET GRADES: 6–12 NEXT GENERATION SCIENCE STANDARDS (NGSS) nextgenscience.org MS-PS1-1 Matter and its HS-PS1-8 Matter and its HS-PS1-1 Matter and its Interactions Interactions Interactions Develop models to describe the Develop models to illustrate the changes Use the periodic table as a model atomic composition of simple in the composition of the nucleus of the to predict the relative properties of molecules and extended structures. atom and the energy released during elements based on the patterns of WKHSURFHVVHVRIoVVLRQIXVLRQDQG electrons in the outermost energy level MS-PS1-4 Matter and its radioactive decay. of atoms. Interactions Develop a model that predicts and HS-PS3-3 Energy HS-PS1-4 Matter and its 'HVLJQEXLOGDQGUHoQHDGHYLFHWKDW describes changes in particle motion, works within given constraints to Interactions temperature, and state of a pure convert one form of energy into another Develop a model to illustrate that the substance when thermal energy is form of energy. release or absorption of energy from a added or removed. chemical reaction system depends upon the changes in total bond energy. HS-PS1-5 Matter and its Interactions $SSO\VFLHQWLoFSULQFLSOHVDQG evidence to provide an explanation LEARNING OBJECTIVES about the effects of changing the temperature or concentration of Students will understand the structure of neon the reacting particles on the rate at atoms and how it can be used to produce neon which a reaction occurs. lights. Students will also explore other forms of luminescence and understand how materials can glow by different processes. Funding for this exhibition was provided by The Pittsburgh Foundation and Advancing Black Arts in Pittsburgh, a joint program of The Pittsburgh Foundation and The Heinz Endowments.
    [Show full text]
  • Chapter 19/ Optical Properties
    Chapter 19 /Optical Properties The four notched and transpar- ent rods shown in this photograph demonstrate the phenomenon of photoelasticity. When elastically deformed, the optical properties (e.g., index of refraction) of a photoelastic specimen become anisotropic. Using a special optical system and polarized light, the stress distribution within the speci- men may be deduced from inter- ference fringes that are produced. These fringes within the four photoelastic specimens shown in the photograph indicate how the stress concentration and distribu- tion change with notch geometry for an axial tensile stress. (Photo- graph courtesy of Measurements Group, Inc., Raleigh, North Carolina.) Why Study the Optical Properties of Materials? When materials are exposed to electromagnetic radia- materials, we note that the performance of optical tion, it is sometimes important to be able to predict fibers is increased by introducing a gradual variation and alter their responses. This is possible when we are of the index of refraction (i.e., a graded index) at the familiar with their optical properties, and understand outer surface of the fiber. This is accomplished by the mechanisms responsible for their optical behaviors. the addition of specific impurities in controlled For example, in Section 19.14 on optical fiber concentrations. 766 Learning Objectives After careful study of this chapter you should be able to do the following: 1. Compute the energy of a photon given its fre- 5. Describe the mechanism of photon absorption quency and the value of Planck’s constant. for (a) high-purity insulators and semiconduc- 2. Briefly describe electronic polarization that re- tors, and (b) insulators and semiconductors that sults from electromagnetic radiation-atomic in- contain electrically active defects.
    [Show full text]
  • Jresv76an6p579 A1b.Pdf
    JOURNAL OF RESEARCH of the National Bureau of Standards-A. Physics and Chemistry Val. 76A, No.6, November- December 1972 Phosphori metry * J. D. Winefordner Department of Chemistry, University of Florida, Gainesville, Florida 32601 (July 26, 1972) Phosphorimetry in the past has received limited use because the precision of re producibility was inadequate, there were solvent limitations, and pre paration of test specimens was difficult and time consuming. Detection limits have now been lowered by more than two orders of magnitude by using a rotating capillary sample cell , a more stable excitation·source power s upply, and aqueous solvents. These steps have also inc reased precision by more than an order of magnitude. Considerable reduction in time and effort of sampling and measurement has been effected compared to phosphorimetric measurements made with standard procedures and comme rcial equipment. Twe nty microliters of aqueous solution is all that is required to fill a quartz capillary cell by capillary action. Capillary cells filled with aq ueous solutions do not crack when cooled to 77 K or when returned to room temperature. Rotation of the sample cell minimizes effects due to cell orientation and thus improves precision. Reduction of background phosphorescence results in improved accuracy of analysis. A study was made of the influence of methanol· water mixtures and of sodium·halide aqueous solutions on the magnitude of phosphorescence signals from several substances and of the e ffe ct on signal·to-noise ratios. The optimum solve nt system for many phosphorimetric measurements is discussed. Analytical results are given for several organic substances measured by phosphorimetry at 77 K.
    [Show full text]
  • Fluorescence and Phosphorescence
    . , . U. S. DEPARTMENT OF COMMERCE -Letter NATIONAL BUREAU OP STANDARDS Circular The Nati information on work- it has done in the field of fluorescence and phosphorescence, or for" information on fluorescent and phosuhor- escent materials or -oti equipment for demonstrating fluorescence and phosphorescence. This letter circular has been prepared in -answer to such requests. It contains information which has been accumulated in answering these letters but it does not represent an exhaustive study of fluorescence (li nor an attempt to make the (1) The term,, fluorescence, will from here on be used to desig- nate both fluorescence and phosphorescence. In common usage the distinction is mainly one of time. Phosphorescent materials con- tinue to emit light after the ekciting radiant energy is turned off, the intensity of this emitted light decreasing continuously with time. In the case of fluorescent materials, the decay is too rapid to be perceptible; hence no light is emitted after the exciting energy ceases. Furthermore, it should be noted that this letter circular considers primarily only that type of luminescence excited by ultraviolet radiant energy, although some of the refer- ences given in sections 1 and 6, below, treat also of other types of luminescence. in case. a information complete any Th references given will , how- ever, serve as a basis for those wishing to pursue the subject further 1. Work of the National Bur eau of Standards i n Fluore scenes No systematic study of the theory or application of fluores- cence has been made at this Bureau, although the following publica tions relating to the subject have been issued: H.
    [Show full text]
  • Introduction to Photochemistry and Light Upconversion
    Introduction to Photochemistry and Light Upconversion CT Japan Photochemistry Workshop Tomoyasu Mani Department of Chemistry University of Connecticut 10/29/2019 1 Department of Chemistry at the University of Connecticut • @ Storrs, CT • 26 tenure‐track or tenured professors • Located in the Chemistry Building • 65 cutting‐edge research and teaching labs 2 From Low to High Upconversion Based on Triplet-Triplet Annihilation https://mani.chem.uconn.edu/photochem-workshop/ 3 Energy Flows High to Low Potential Energy © Science Media Group. ©The McGraw‐Hill 4 Energy Flows Low to High ?? Potential Energy ©The McGraw‐Hill 5 What is Photochemistry? The chemistry concerned with the chemical effects of light. Generally, a chemical reaction is caused by using UV, visible, infrared light. 700 nm 600 nm 500 nm 400 nm 6 Why Important? Photosynthesis is Driven by Light! We can see “inside” by Light! 7 Converting Light to Something Else. Making Molecules with Light. Making Electricity from Light. 8 What is Going On? General Jablonski Diagram Singlet Manifold S3 S2 IC S1 Energy Photon Fluorescence Absorption Ground State IC = internal conversion 9 Photoexcitation = Excess Energy Singlet Manifold Excited S3 S2 IC S1 Energy Photon Fluorescence Absorption Ground Ground State State IC = internal conversion 10 Fluorescence Emission BLUE Light https://cen.acs.org/biological-chemistry/biotechnology/Chemistry-Pictures-Laser-activated/97/web/2019/08 11 What is Going On? General Jablonski Diagram Singlet Manifold Triplet Manifold S3 T3 S2 T2 IC Triplet-triplet absorption
    [Show full text]
  • 5. Fluorescence Applications
    POWER LIGHTS FOR MACHINE VISION 5. Fluorescence applications UV lighting is always used in cases where materials require excitation in order to ‘glow’. While the excitation Influence of the wavelength will depend on the fluorescent medium used, it may be found anywhere within the complete spectrum lighting angle – from ultraviolet to near infrared. Since industrial processes primarily involve the use of ultraviolet radiation, this part of our Knowledge Base focuses on applications using ultraviolet irradiation. Fluorescence applications are needed in a wide variety of industries. Wavelengths A brief overview of typical applications: ■ Inspection of adhesives, paints, sealants and lubri- cants ■ Inspection of safety features and markings as pro- tection against fake and counterfeit goods Optical filters ■ Product labelling ■ Track & Trace ■ Analysis of residues/residual soiling ■ Crack, cavity and defect inspection ■ Forensic analyses Flash vs. continuous Track & Trace in the pharmaceutical industry The ‘glowing’ described above is luminescence, the generation of light from matter. Luminescence is the optical radiation that occurs during the transition from a stimulated state to the basic state. A key distinction is made between fluorescence and phosphorescence. Fluorescence applications ■ With fluorescence, a material emits light while being stimulated, i.e. it starts to glow on exposure to radiation at a certain wavelength. However, this glowing fades as soon as the irradiation ceases. ■ Phosphorescence describes a similar effect, although
    [Show full text]
  • The Power of Light! Light and Luminescence Science
    The Power of Light! Light and Luminescence Science Friday Funday Laboratory Notebook Name: Team: Experiment #1: Chemiluminescence – Building a Glowstick Guess how glow sticks work before beginning the experiment. Background: During chemical reactions between substances energy may be released. In most cases, energy will be released in the form of heat. However, in some reactions, energy can instead be released in the form of light. In this experiment we’ll examine the phenomena known as chemiluminescence, wherein a reaction will release light but not heat. Procedure (Check off the circles as you complete): o Acquire 5 centrifuge tubes (10 mL) with caps. Label them A-E. o Acquire a small graduated cylinder. o Acquire the four dye packets, labeled: Eosin Y (Orange Dye) Rhodamine B (Red Dye) 9,10-bis(phenlethynl)anthracene (Green Dye) Fluorescein (Yellow Dye) o Measure 5 mL of Luminol into each of your 5 centrifuge tubes. o Pour the four dyes into individual centrifuge tubes; leave one centrifuge tube without dye. o Add 5 mL of 30% Hydrogen Peroxide into each centrifuge tube. o Cap the tubes tightly and shake. Safety Alert: Hydrogen Peroxide is toxic! Do not open the tube! Observations: Observe the different colors and intensities (bright, slightly bright, mostly dim, dim): Write your observations below in the tubes labeled A-E. A B C D E Compare the colors to the visible spectrum: What do the different wavelengths mean? Why are some of the reactions brighter than others? Do the tubes feel warm? Is there still energy being released? What kind of energy? Experiment #2: Fluorescence, Black Lights, and Sunscreen: Background: In the previous reaction, energy held in chemical bonds was converted to energy in the form of light.
    [Show full text]
  • Interplay of Fluorescence and Phosphorescence in Organic
    Interplay of Fluorescence and Phosphorescence in Organic Biluminescent Emitters Caterin Salas Redondo,1,2 Paul Kleine,1 Karla Roszeitis,1 Tim Achenbach,1 Martin Kroll,1 Michael Thomschke,1 and Sebastian Reineke*1,2. 1 Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Nöthnitzer Straße 61, D-01187, Germany. 2 Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden, Würzburger Straße 46, D-01187 Dresden, Germany. AUTHOR INFORMATION Corresponding Author *Sebastian Reineke. E-mail: [email protected] 1 ABSTRACT Biluminescent organic emitters show simultaneous fluorescence and phosphorescence at room temperature. So far, the optimization of the room temperature phosphorescence (RTP) in these materials has drawn the attention of research. However, the continuous wave operation of these emitters will consequently turn them into systems with vastly imbalanced singlet and triplet populations, which is due to the respective excited state lifetimes. This study reports on the exciton dynamics of the biluminophore NPB (N,N’-di(1-naphthyl)-N,N’-diphenyl-(1,1-biphenyl)-4,4- diamine). In the extreme case, the singlet and triplet exciton lifetimes stretch from 3 ns to 300 ms, respectively. Through sample engineering and oxygen quenching experiments, the triplet exciton density can be controlled over several orders of magnitude allowing to studying exciton interactions between singlet and triplet manifolds. The results show, that singlet-triplet annihilation reduces the overall biluminescence efficiency already at moderate excitation levels. Additionally, the presented system represents an illustrative role model to study excitonic effects in organic materials. KEYWORDS: biluminescence, room temperature phosphorescence, dual state emission, organic semiconductors, organic emitters.
    [Show full text]
  • Photochemistry Is the Underlying Mechanism for All of Photobiology
    Photochemistry Photochemistry • Photochemistry is the underlying mechanism for all of photobiology. When a molecule absorbs a photon of light, its electronic structure changes, and it reacts differently with other molecules. The energy that is absorbed from light can result in photochemical changes in the absorbing molecule, or in an adjacent molecule (e.g., photosensitization). The energy can also be given off as heat, or as lower energy light, i.e., fluorescence or phosphorescence, in order to return the molecule to its ground state. Each type of molecule has a different preference for which of these different mechanisms it uses to get rid of absorbed photon energy, e.g., some prefer fluorescence over chemistry. The Basic Laws of Photochemistry • The First Law of Photochemistry The First Law of Photochemistry states that light must be absorbed for photochemistry to occur. This is a simple concept, but it is the basis for performing photochemical and photobiological experiments correctly. If light of a particular wavelength is not absorbed by a system, no photochemistry will occur, and no photobiological effects will be observed, no matter how long one irradiates with that wavelength of light. The Second Law of Photochemistry • The Second Law of Photochemistry states that for each photon of light absorbed by a chemical system, only one molecule is activated for a photochemical reaction. This law is true for ordinary light intensities, however, with high-powered lasers, two- photon reactions can occur, i.e., the molecule is raised to a higher energy state than produced by single-photon absorption. Laws of Photochemistry 1. Only light that is absorbed can produce photochemical change (Grotthus, Draper) 2.
    [Show full text]