This document discusses the principle and applications of phosphorescence. Phosphorescence occurs when a material absorbs light and enters an excited state, then slowly emits light as it transitions from a triplet excited state to a ground singlet state. Common phosphors use transition metal compounds or rare earth elements as the host material doped with an activator. Phosphors have various applications including in lighting such as fluorescent lamps, glow-in-the-dark toys which use calcium or strontium sulphide phosphors, white LEDs which combine blue LEDs with yellow phosphors, and electroluminescent displays.

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2. CONTENTS
 Introduction
 Principle of Phosphorescence
 Mechanism
 Applications of Phosphorescence-
-Lightning -Phosphor Thermometry
-Glow in dark toys -Luminescence
-White LEDs -Electroluminescence
 Conclusion
 References
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3. Introduction
 A phosphor, most generally is a substance that exhibits
the phenomenon of luminescence.
 Phosphors are commonly transition metal compounds
or rare earths.
 But the element Phosphorus named for its light
emitting behaviour due to chemiluminescence not due
to phosphorescence.
 Common pigments used in phosphorescent materials
include Zinc Sulphide and Strontium aluminate.
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4.  Objects coated with phosphors that absorb UV light
resulting in the emission of visible light over an
extended period of time.
 Phosphors keep some of the energy and release some
of the lower energy as visible light.
 E.g. Glow in the dark
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5. Principle of phosphorescence
 Any material absorbs light and enter in exited state,
then the emission of energy from triplet state to
ground singlet state is phosphorescence.
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6. Applications
 Lightening
 Phosphor thermometry
 Glow in dark toys
 White LEDs
 Electroluminescence
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7. .Lightening
 Phosphor layers provide most of the light produced by
fluorescent lamps.
 Various Neon signs use phosphor layers to produce
different colours of light.
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8. Phosphor Thermometry
 It is a temperature measurement approach that uses
the temperature dependence of certain phosphors.
 A phosphor coating is applied to a surface of interest
and usually the decay time is the emission parameter
that indicates temperature.
 The method may be used for moving surfaces such as
high speed motor surfaces
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9. Glow in dark toys
 Calcium sulphide with Strontium sulphide with
Bismuth as activator (Ca,Sr)S:Bi yields blue light (glow
times upto 12 hours).
 Red colour can be obtained from Strontium sulphide.
 Mix of Zinc sulphide and Cadmium sulphide emit
colour depending on their ratio.
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10. White LEDs
 White Light Emitting Diodes are usually blue InGaN
LEDs with a coating of suitable material.
 This coated material absorbs the light from blue LED
and emits in a broad range from greenish to reddish.
 Mostly output is yellow.
 This yellow emission combined with the remaining
blue emission gives the “white” light.
 This white light can be adjusted to colour temperature
as warm(yellowish) or cold(bluish) white.
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11. Electroluminescence
 Luminescence in light sources is known as
Electroluminescence.
 The excitation of the phosphor is usually achieved by
application of by application of electric field with
suitable frequency.
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12. Conclusion
 A phosphor- the substance that exhibits the process of
luminescence.
 Phosphors are usually made from a suitable host
material with an added activator. The best known type
is Copper activated Zinc sulphide.
 These are widely used in LEDs.
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13. References
 1. Cuba, V., Pavelkova, T., Barta, J., Jarý, V., Nikl, M.,
Jakubec, I. Photo- and radiation induced preparation of
Y2O3 and Y2O3:Ce(Eu) nanocrystals. J. Nanoparticle
Research, 2012, 14, 794-801.
 2. Yen W.M., Raukas M., Basun S. A., van Schaik W.,
Happek U., Optical and photoconductive properties of
cerium doped crystalline solids. J Lumin. 1996, 69, 287–294
 3. Cuba, V., Indrei, J., Mucka, Nikl, M., Beitlerova, A.,
Pospisil, M., Jakubec, I.. Radiation induced synthesis of
powder yttrium aluminium garnet. Radiation Physics and
Chemistry, 2011, 80, 957-62.
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