Flourescence & Phosphorescence


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Flourescence & Phosphorescence

  2. 2. Prepared & Presented by: Sidra Safdar Durrani M.Sc. Final year Presented to: Ms. Dr. Abida Parveen For the Course of: Photochemistry & Radiation Chemistry
  3. 3. 4 WHAT IS MOLECULAR LUMINESCENCE ?  Chemiluminescence  Phosphorescence  Molecular Fluorescence excitation resulting from a chemical reaction excitation by absorption of photons: PHOTOLUMINESCENCE  BASIC PRINCIPLE: 1st: molecules are excited (outer shell electrons like in absorbance phenomenon) 2nd: excited species give an emission spectrum that provides information for quantitation and qualification Fluorescence is short-lived, with luminescence ceasing almost immediately (<10-5 sec) ,while phosphorescence features luminescence from 10-4 to several seconds.
  4. 4. 5 HISTORY
  5. 5. 6 SINGLET AND TRIPLET STATES excited singlet state Excited triplet state is of less energy than excited singlet state. Singlet to triplet transitions are far less probable than singlet/singlet transitions. excited triplet state ground state PAULI EXCLUSION PRINCIPLE: ―no two electrons in an atom can have the same set of 4 quantum numbers‖, in other words: two electrons in the same orbital must have opposite spins (we say: they are "paired": no net magnetic field = the molecule will be "diamagnetic"), molecule with unpaired electrons (e.g. triplet state) possess magnetic moment, are attracted by magnetic field, are called "paramagnetic" Physicochemical properties of molecules in triplet state can differ significantly from those of singlet state molecules.
  6. 6. 7 E L E C T R ON IC A N D V IB R A T ION A L LEVELS  S0: ground state of a molecule at ambient temperature, all of the molecules in a solution  S1 and S2: excited singlet states  T1: lowest energetic triplet state, usually of less energy than lowest energetic excited singlet state S1. Same E S1 Each of these states features various vibrational levels – this permits energetic T1 similarity (and even equivalence) of different electronic spin states of a molecule. Because Singlet / triplet transitions are less probable than singlet / singlet transition (because spin conversion is necessary) , thus the average lifetime of an excited triplet state is 10-4 sec and more, while excited singlet state lifetime is 10-8 to 10-5 s.
  7. 7. 8 ELECTRON TRANSITIONS INTERSYSTEM CROSSING S2 S1 High E, Short λ Low E, Long λ Energy T1 S0 VIBRATIONAL RELAXATION due to collisions between the molecules of the excited species and those of the solvent vibrational levels λ1 absorption λ2 λ3 INTERNAL CONVERSION when 2 levels are sufficiently close energetically. (reversal of spin), common in molecules containing heavy atoms or when paramagnetic species are present (O2 in solution)  fluorescence is decreased. FLUORESCENCE always from lowest vibrational level of an excited electronic state PHOSPHORESCENCE Deactivation from an ‘triplet” electronic state to the ground state producing a photon
  8. 8. 9 VIBRATIONAL RELAXATION I  1st Observation : Upon excitation different vibrational levels can be achieved, in solution any excess vibrational energy is lost as consequence of collisions between the molecules of the excited species and solvent molecules  Result: Energy transfer to solvent and minuscule warming, lifetime of vibrational excited species: 10-12 sec and less.  Consequence: Fluorescence (and Phosphorescence) of an analyte in solution always occurs due to electron transition from a vibrational ground state.
  9. 9. 10 VIBRATIONAL RELAXATION II 2 n d O b s e r v a t i o n : Upon luminescence different vibrational levels can be achieved, in solution any excess vibrational energy is lost as consequence of collisions between the molecules of the excited species and solvent molecules  Consequence I: fluorescence (and phosphorescence) of an analyte do not give sharp signals but diffuse bands. C o n s e q u e n c e I I : T h e fluorescence spectrum of an analyte often is more or less similar to its absorbance spectrum.
  10. 10. Fluorescence – ground state to singlet state & back Phosphorescence -ground state to triplet state & back Fluorescence 10-5 to 10-8 s Phosphorescence 10-4 to 10 s Example of Phosphorescence 0 sec 1 sec 11
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  12. 12. 13 PHOSPHORESCENCE After intersystem crossing from singlet to triplet state, deactivation can occur by internal or external conversion or by phosphorescence. Since triplet-to-singlet conversions are comparatively improbable events, the average lifetime of an excited triplet state is 10-4 to 10 sec and more. Thus, emission from such transition may persist for some time after irradiation has been discontinued. The other deactivation transitions compete strongly with phosphorescence, so this phenomenon is usually observed at low temperatures, in highly viscous media or at molecules being adsorbed on surfaces. T1 S0
  13. 13. 14 THE SHAPE OF LUMINESCENCE SPECTRA 1. Phosphorescence and Fluorescence (emission) Spectrum both come at longer wavelengths compared to absorbance spectrum of the same molecule (Stokes shift). 2. Phosphorescence comes at lower energy = at longer wavelengths than fluorescence from the same molecule. 3. Fluorescence (emission) Spectrum of a molecule is more or less similar to its absorbance spectrum.
  14. 14. 15 How does glow-in-the-dark stuff work? You see glow-in-the-dark stuff in all kinds of places, but it is most common in toys like a glow-in-the-dark yo-yo, a glow-in-the-dark ball, a glow-in-the-dark mobile. If you have ever seen any of these products, you know that they all have to be "charged". You hold them up to a light, and then take them to a dark place. In the dark they will glow for 10 minutes. Some of the newer glow-in-the-dark Light stick activation stuff will glow for several hours. occurs by simply cracking a A color TV screen actually contains light stick and allowing the thousands of tiny phosphor picture chemicals to mix. elements that emit three different colors (red, green and blue). In the case of a fluorescent light, there is normally a mixture of phosphors that together create light that looks white to us.
  15. 15. 16 Each of PTI's diverse and versatile fluorometer systems is designed with particular user needs in mind. The Quanta Master™ 30 is a bench-top fluorometer that utilizes a pulsed excitation source. The Quanta Master™ 30 is the most sensitive fluorescence system using a pulsed light source however if you ONLY require intensity based measurements PTI'sQuantaMaster™ 40 is recommended.
  16. 16. INSTRUMENTATION BASIC DESIGN • components similar to UV/Vis • spectrofluorometers: observe • both excitation & emission spectra. Extra features for phosphorescence • sample cell in cooled Dewar flask with liquid nitrogen • delay between excitation and emission
  17. 17. 18 LIGHT SOURCES OF FLUOROMETERS  IN SPECTROFLUORIMETER : CONTINUOUS RADIATION REQUIRED i) 75- to 450W high pressure xenon arc lamp, emitting 300 to 1300 nm large power supply needed (5 to 20 A at 15 to 30 V) ii) tunable dye LASERs – comparatively expensive; advantages: suitable for small samples ( L or less), if highly monochromatic excitation is required, or for remote sensing
  18. 18. 19 OTHER PARTS OF FLUOROMETERS  EXCITATION AND EMISSION MONOCHROMATOR:  interference and absorption filters for filter fluorometers  grating monochromators for spectrofluorimeter  SAMPLE CELL:  cylindrical and rectangular cells of glass or quartz  any fingerprints are even more disturbing than in absorbance spectroscopy
  19. 19. 20 OTHER PARTS OF FLUOROMETERS  DETECTOR:  the most common transducers are photomultiplier tubes (PMT) run in photon counting mode  the final detector output (fluorescence signal) is the ratio (division!) between the sample beam’s PMT signal intensity and the reference beam’s PMT signal photon counting mode (applied for low intensity radiation): analog signal is converted to a train of digital pulses  radiant power is proportional to the number of pulses per unit time.
  20. 20. 21 APPLICATIONS TELEVISION TUBES ALSO USE PHOSPHORESCENCE. The tube itself is coated with phosphor, and a narrow beam of electrons causes excitation in a small portion of the phosphor. The phosphor then emits red, green, or blue light—the primary colors of light—and continues to do so even after the electron beam has moved on to another region of phosphor on the tube. As it scans across the tube, the electron beam is turned rapidly on and off, creating an image made up of thousands of glowing, colored dots. Cutaway rendering of a color CRT: 1. Three Electron guns (for red, green, and blue phosphor dots) 2. Electron beams 3. Focusing coils 4. Deflection coils 5. Anode connection 6. Mask for separating beams for red, green, and blue part of displayed image 7. Phosphor layer with red, green, and blue zones 8. Close-up of the phosphor-coated inner side of the screen
  21. 21. 22 APPLICATIONS PHOSPHORESCENT PIGMENTS Our Phosphorescent pigments are a new type of long persistence phosphorescent pigment of alkaline earth aluminate activated by rare earth ions. The new type of pigment is used for many very different technical and artistic purposes due to its characteristics. It can be used in manufacturing paint; ink; plastic; rubber and films etc. It is completely safe for the application in consumer products such as clothing; shoes; caps; toys; stationery goods; watch; switch; novelties; fishing tools and sporting goods. It has good effects in the fields of building; decoration; traffic vehicle; military installations; fire emergency system. It is especially suitable for the production of long afterglow safety products such as warning; mandatory and escaperoute signs.
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