The document discusses luminescence, a phenomenon where materials emit light after absorbing energy, with a focus on photoluminescence which includes fluorescence and phosphorescence. Fluorescence occurs almost instantaneously after excitation, while phosphorescence can result in light emission over minutes to days. Applications include fluorescent lamps and display devices that harness these luminescent properties for improved visual output.

1. LUMINESCENCE
 BY MANEESH
TIWAREE
 (NIT
NAGALAND)


2. INTRODUCTION
An electron absorbs a photon from the incident beam
and it jumps from valance band to the conduction
band. Thus ,this electron is in exited state or higher
state ,but it no longer be in the higher state and
eventually get back into lower energy state by
emitting radiation.
This phenomenon of emission of light by
a material after absorbing such type of energy ,is
known as luminescence.
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3. CONTENTS
Photoluminescence
Fluorescence
Phosphorescence
Application of luminescence
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4. PHOTOLUMINESCENCE
Photoluminescence is a type of
luminescence.
The process in which the emitting
radiation arises due to the absorption of
photon from the source such as
infrared,visible,ultravoilet or x-rays.
Photoluminescence is divided into two parts
namely,fluroscence and phosphorescence.
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5. FLUORESCENCE
If a material absorbs light by any one of the
above intorduced source ,it radiates or emit
light within 10-8 sec. after the excitation is
removed. This luminescence is known as
fluorescence or fast photoluminescence.
It is a temperature independent phenomenon.
Substance like fluorspar,fluorescein,quinine
sulphate,uranium oxide,calcite,uranium glass
exhibit the phenomena of fluorescence.
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6.  Characterstic luminescent materials
 Activator ion
 Stokes effect- The same energy levels are involved for both
absorption and emission and hence,the wavelengths are
identical . The only difference between the two wavelegnths is a
shift in the emission spectrum towards the red end of the
absorption spectrum . This phenomenon is known as stokes
effect .
Reason: when the activator gets exited state ,gives up heat
energy to surrounding by means of vibration,this loss of energy
is the reason behind stokes shift.
Application : fluorescent lamps.
Therefore ,in Characterstic luminescent materials,the excitation
and emission ofolumi light takes place very rapidly in less than
10-8 s and hence called as fast photoluminescence.
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7. 6

8. PHOSPHORESCENCE
Certain materials emit light after the incident
radiaton is cut off. This process is known as
phosphorescence. The time delay between
the excitation of electron and emission of
light ranges from 10-8 s to several min.or
Hrs. Or even days.
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9.  Non-Characterstic luminescent materials
 Activator
 Coactivators
 Hole trap(acceptor energy level)
 Electron trap(donor energy level)
 Electron -hole generation and recombination
process
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10. Electron- hole generation
Ec
Ed
Ea
Ev
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11. Holes trapped into acceptor sites
Ec
Ed
Ea
Ev
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12. Trapping of electron occur at donor site
Ec before
recombination
Ed
Ea
Ev 11

13. Electron recombined with hole and hence
Ec release a
luminescent
radiation.
Ea
Ev
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14.  The time taken by the electron in a trap depend
on the depth of the trap below conduction band
Ec- Ed
 The emission of electron slow due to the
electron hole recombination through impurity
levels.
Therefore ,this process is known as slow
photoluminescence.
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15. PHOSPHORS
Materials are used to produce luminescence.
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BASE MATERIALS ACTIVATORS LIGHT
COLOURS
Zinc sulfide Silver Blue
Yttrium silicate cerium Purple blue
Zinc sulfide copper green
Gadolium oxysulfide terbium Yellowish
green
Zinc orthosilicate Manganese Yellowish
green
Zinc cadmium
sulfide
Silver Green
Yttrium oxysulfide Europium Red

16. APPLICATIONS
 Fluorescent materials are used in display devices
such as LED,LCD,CRT etc.
 A Fluorescent lamp consist of a thin coating of
Fluorescent materials like cadmium borate zinc
silicateetc. When uv radiation fall on it ,and they
absorbs incident radiation and re-emit the light having
the wavelength in visible region ,and hence,
increases luminous flux.
 When x-rays are made to fall on glass coated with
such materials produces fluorescent light. Therefore it
is used as a x-ray detector.
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17. REFERENCES
 https://en.wikipedia.org/wiki/Stokes_shift
 Materials science (v rajendran)
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18. PHOTOLUMINESCENCE
Presntation given by-
MANEESH
TIWAREE
(2014466003)
Under the supervision of –
DR.DEBRUN DHAR
PURKYASTHA
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