Presentation related to Photochemistry & Radiation chemistr

2. PHOSPHORESCENCE
SPECTROSCOPY
Quinine
2

3. Prepared & Presented by:
Sidra Safdar Durrani
M.Sc. Final year
Presented to:
Ms. Dr. Abida Parveen
For the Course of:
Photochemistry &
Radiation Chemistry

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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.

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HISTORY

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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.

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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.

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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

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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.

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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.

11. 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
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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

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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.

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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.

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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.

17. 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

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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

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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

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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.

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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

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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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