<< Chapter < Page Chapter >> Page >
This is the continuation of Chapter 1_Part 7 where we describe the resonant transition , fluorescence, phosphorescence and we bring out the distinction between spontaneous and stimulated emission.

SSPD_Chapter1_Part7continued_ ATOMIC ENERGY EXCHANGES AND PHYSICS OF GAS DISCHARGE TUBES.

Atomic Energy Exchanges are governed by resonance phenomena. If the incident photon energy is approximately equal to the transition energy then photon is said to resonate with transition and the excitation of the electron at the given transition is favored.

For 1 electron atom:

P(transition)= (SinӨ/Ө)^ 2 = Sinc^ 2 (Ө) = Sin^ 2 [π(ν ko -ν)t]/[ π(ν ko -ν)t]^ 2 1.40

Where P(transition) is the probability of transition from ground state to the excited state k.

( Zambuto, Mauro: Handbook of Electrical and Computer Engineering (ed. Sheldon S.L. Chang) , Vol.1, pp. 597- 623, John Wiley&Sons, Inc, New York, 1994;

Leighton, Robert A. Principles of Modern Physics, McGraw Hill, New York, 1954 )

Transition Energy from ground state to excited state = h ν ko = (E n – E 0 );

Incident Photon Energy = h ν;

t = duration of interaction;

For reasonable interaction duration, only incident photon with frequency ν = ν ko will induce excitation. Therefore only resonant photons are absorbed. To the rest of the photons, the atom appears to be transparent.

Probability of Absorption is sharply peaked at resonance as shown in Fig.(1.18)

Fig.(1.18) Probability of Absorption is given by (SincӨ) 2 where Ө= π(ν ko -ν)t

Spontaneous Emission Phenomena .:

When an excited atom returns to ground state in the natural course of events and in the process emits a photon equal to the transition energy , we say spontaneous emission has taken place. This process of spontaneous emission is also known as relaxation.

When relaxation is in nanosecond, we have fluorescence effect. In fluorescence the excited atom relaxes by emitting a lower frequency photon as compared to the higher frequency absorbed. The difference between absorbed and emitted is lost due to collisions with other molecules. The energy absorbed resides in the molecule as rotational energy, vibrational energy and as excited electron energy. The lowering of emitted photon takes place due to the loss of a part of the vibrational energy. We will have a detailed discussion on this topic in the last section, specific heat section, of this Chapter.

When relaxation is in micro and millisecond, we have phosphorescence effect. The photo emission is delayed and prolonged. Here the absorption of photon causes the transition from ground singlet state to excited singlet state. In singlet state total spin quantum number is S =0. Due to collisions with other molecules, the excited singlet state loses a part of vibrational energy and suffers a radiationless transition to excited triplet state (S=1) . The energy difference between the vibrational energy states is lost as the thermal energy of the gas molecules. Now a radiative transition from excited triplet state to ground singlet state is forbidden by SELECTION RULE [ Appendix XXXI A]. Though forbidden nevertheless after some time the excited triplet molecule does relax to the ground singlet state thus giving rise to a delayed and prolonged emission. This is termed as Phosphorescence. The delayed emission may occur after minutes or even after hours depending upon the composition of phosphorescence screen.

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Solid state physics and devices-the harbinger of third wave of civilization. OpenStax CNX. Sep 15, 2014 Download for free at http://legacy.cnx.org/content/col11170/1.89
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Solid state physics and devices-the harbinger of third wave of civilization' conversation and receive update notifications?

Ask