Absorption and Emission - Revision history

Cmditradmin: /* Transitions and vibrational levels */

2010-07-07T17:33:13Z

Transitions and vibrational levels

← Older revision		Revision as of 10:33, 7 July 2010
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	[[Image:Potentialenergy_surfacechang.png\|thumb\|400px\|The potential energy surface of the ground state and of the excited state.The potential energy surface of the ground state varies over about 2 eV.]]		[[Image:Potentialenergy_surfacechang.png\|thumb\|400px\|The potential energy surface of the ground state and of the excited state.The potential energy surface of the ground state varies over about 2 eV.]]

	The abscissa of this graph is the deformation coordinates, which is how the system deforms; the modifications in the coordinates of the system. The lower figure is the optimal geometry of the ground state, and it is different from the optimal geometry of the S<sub>1</sub> state that is shown above. The two potential energy surfaces are displaced with respect to one another. The larger the relaxation in the excited state, the larger the geometry of the modification in the excited state, and thus, the larger the displacement would be. If the geometry in the excited state were to be exactly the same as in the ground state, then the two potential energy curves would sit on top of one another. The vibrational levels corresponding to those C-C stretching modes are connected to the geometry relaxation in the excited state and therefore, they are connected to the electronic transition. The dashed curves show the zero vibrational level, the first vibrational level, the 2nd vibrational level and so on. At room temperature, the vibrational mode has energy of on the order of 0.15 to 0.2 electron volts. The energy difference between the zeroth vibrational level and the first vibrational excitation is higher than the kinetic energy available at room temperature(room temperature Kt is 0.025eV). In other words, in the ground state, basically all of the oligomers or polymers are in the zeroth vibrational level.		The abscissa of this graph is the deformation coordinates, which is how the system deforms; the modifications in the coordinates of the system. The lower figure is the optimal geometry of the ground state, and it is different from the optimal geometry of the S<sub>1</sub> state that is shown above. The two potential energy surfaces are displaced with respect to one another. The larger the relaxation in the excited state, the larger the geometry of the modification in the excited state, and thus, the larger the displacement would be. If the geometry in the excited state were to be exactly the same as in the ground state, then the two potential energy curves would sit on top of one another. The vibrational levels corresponding to those C-C stretching modes are connected to the geometry relaxation in the excited state and therefore, they are connected to the electronic transition. The dashed curves show the zero vibrational level, the first vibrational level, the 2nd vibrational level and so on. At room temperature, the vibrational mode has energy of on the order of 0.15 to 0.2 electron volts. The energy difference between the zeroth vibrational level and the first vibrational excitation is higher than the kinetic energy available at room temperature(room temperature kT is 0.025eV). In other words, in the ground state, basically all of the oligomers or polymers are in the zeroth vibrational level.

	The curve of the dotted lines is the vibrational wave function. In the vibrational ground state, there is no node. In the first excitation state there is one node, and in the 2nd vibrational excited state there are 2 nodes, and so on. The same thing is what you would have if you were to simply look at a particle in the box. In the vibrational ground state, the largest probabilities to find the molecule or the polymer is in the middle. That is the state when the photons strike. The transition takes place faster than the geometry relaxation and thus, there is a vertical transition. Since the potential energy curves are displaced, if you start from the most probable situation in the ground state, and go up, you can have the largest overlap of the vibrational wave functions with the first or the second vibrational level. When there is a coupling of the electronic transition with vibrational modes, the intensity of your electronic transition is modulated by the overlap of the vibrational wave functions as you go up the excited state potential energy surface.		The curve of the dotted lines is the vibrational wave function. In the vibrational ground state, there is no node. In the first excitation state there is one node, and in the 2nd vibrational excited state there are 2 nodes, and so on. The same thing is what you would have if you were to simply look at a particle in the box. In the vibrational ground state, the largest probabilities to find the molecule or the polymer is in the middle. That is the state when the photons strike. The transition takes place faster than the geometry relaxation and thus, there is a vertical transition. Since the potential energy curves are displaced, if you start from the most probable situation in the ground state, and go up, you can have the largest overlap of the vibrational wave functions with the first or the second vibrational level. When there is a coupling of the electronic transition with vibrational modes, the intensity of your electronic transition is modulated by the overlap of the vibrational wave functions as you go up the excited state potential energy surface.

Cmditradmin at 20:05, 29 December 2009

2009-12-29T20:05:05Z

← Older revision		Revision as of 13:05, 29 December 2009
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			[[category:absorption]]
			[[category:luminescence]]
	<table id="toc" style="width: 100%">		<table id="toc" style="width: 100%">
	<tr>		<tr>

Cmditradmin: /* Stokes Shifts */

2009-09-15T21:00:39Z

Stokes Shifts

← Older revision		Revision as of 14:00, 15 September 2009
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	=== Stokes Shifts ===		=== Stokes Shifts ===

	[[Image:Abs_Emis_stokes.png\|thumb\|300px\|~~Emission~~ an absorption are offset from each other]]		[[Image:Abs_Emis_stokes.png\|thumb\|300px\|With a Stokes shift emission an absorption are offset from each other]]

	Absorption starts at 0-0 and then 0-1, 0-2, 0-3, 0-4, and so on. The 0-2 absorption is the most intense. If the energy of the vibrational mode is 0.2 eV, or if 0-2 is the most intense, there is a relaxation of about 0.4 eV in the excited state because the transition from the zeroth vibrational level of the ground state to the 2nd vibrational level of the electronic excited state is most dominant. From that 2nd vibrational level, the system will trickle down to the zeroth vibrational level for a total of change of 0.4 eV.		Absorption starts at 0-0 and then 0-1, 0-2, 0-3, 0-4, and so on. The 0-2 absorption is the most intense. If the energy of the vibrational mode is 0.2 eV, or if 0-2 is the most intense, there is a relaxation of about 0.4 eV in the excited state because the transition from the zeroth vibrational level of the ground state to the 2nd vibrational level of the electronic excited state is most dominant. From that 2nd vibrational level, the system will trickle down to the zeroth vibrational level for a total of change of 0.4 eV.

Cmditradmin: /* Vibronic Progression */

2009-09-15T20:46:15Z

Vibronic Progression

← Older revision		Revision as of 13:46, 15 September 2009
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	Vibronic progression can be seen in the absorption and emission spectra. Vibronic progression means that there is a coupling to vibrational modes in a polymer or oligomer resulting in excitation from the ground state to the excited state, or emission from the excited state down to the ground state.		Vibronic progression can be seen in the absorption and emission spectra. Vibronic progression means that there is a coupling to vibrational modes in a polymer or oligomer resulting in excitation from the ground state to the excited state, or emission from the excited state down to the ground state.
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	=== Change in excited state geometry ===		=== Change in excited state geometry ===

Cmditradmin: /* Vibronic Progression */

2009-09-15T20:46:00Z

Vibronic Progression

← Older revision		Revision as of 13:46, 15 September 2009
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	=== Vibronic Progression ===		=== Vibronic Progression ===
	[[Image:Abs_Emis_stokes.png\|thumb\|~~300px~~\|Emission and absorption spectra showing vibronic structure]]		[[Image:Abs_Emis_stokes.png\|thumb\|200px\|Emission and absorption spectra showing vibronic structure]]

	Vibronic progression can be seen in the absorption and emission spectra. Vibronic progression means that there is a coupling to vibrational modes in a polymer or oligomer resulting in excitation from the ground state to the excited state, or emission from the excited state down to the ground state.		Vibronic progression can be seen in the absorption and emission spectra. Vibronic progression means that there is a coupling to vibrational modes in a polymer or oligomer resulting in excitation from the ground state to the excited state, or emission from the excited state down to the ground state.

Cmditradmin: /* Vibronic Progression */

2009-09-15T20:45:52Z

Vibronic Progression

← Older revision		Revision as of 13:45, 15 September 2009
Line 10:		Line 10:

	=== Vibronic Progression ===		=== Vibronic Progression ===
			[[Image:Abs_Emis_stokes.png\|thumb\|300px\|Emission and absorption spectra showing vibronic structure]]

	Vibronic progression can be seen in the absorption and emission spectra. Vibronic progression means that there is a coupling to vibrational modes in a polymer or oligomer resulting in excitation from the ground state to the excited state, or emission from the excited state down to the ground state.		Vibronic progression can be seen in the absorption and emission spectra. Vibronic progression means that there is a coupling to vibrational modes in a polymer or oligomer resulting in excitation from the ground state to the excited state, or emission from the excited state down to the ground state.

Cmditradmin at 21:12, 1 September 2009

2009-09-01T21:12:43Z

← Older revision		Revision as of 14:12, 1 September 2009
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	Absorption and emission are often used as characteristics that help identify substances. In photonics they are ~~actually~~ the core ~~phenomena that~~ molecules ~~are designed for~~. Materials can be designed that absorb light at one wavelength and emit it at another. Specific colors need to be matched to the application that the materials are intended for. Theory helps explain why molecules behave as they do and provide guidance for manipulating their design.		Absorption and emission are often used as characteristics that help identify substances. In photonics they are the core properties of molecules which make them useful. Materials can be designed that absorb light at one wavelength and emit it at another. Specific colors need to be matched to the application that the materials are intended for. Theory helps explain why molecules behave as they do and provide guidance for manipulating their design.

	=== Vibronic Progression ===		=== Vibronic Progression ===

Cmditradmin: /* Simulation of Emission */

2009-09-01T16:53:15Z

Simulation of Emission

← Older revision		Revision as of 09:53, 1 September 2009
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	As soon as the energy of the photon is large enough, any molecule in the thin film will be able to absorb. Remember that the excited state has a given life time on the order of nanoseconds. During that life time, the excited state on a slightly distorted molecule can jump on a less distorted molecule and therefore, have a smaller excited state energy. Since the system is more conjugated, the band gap is smaller and the excited state energy is smaller. Therefore, what will happen is that the excitation will move across the material and will get to the most perfectly conjugated molecules because these are the ones for which the energy of the excited state is smallest. Because they emit only from the most well conjugated molecules, the emission will be from a single species where as in absorption, you can have not only the most conjugated but also the slightly distorted molecules that will also absorb. Absorption will indicate disorder in the system much more than emission will.		As soon as the energy of the photon is large enough, any molecule in the thin film will be able to absorb. Remember that the excited state has a given life time on the order of nanoseconds. During that life time, the excited state on a slightly distorted molecule can jump on a less distorted molecule and therefore, have a smaller excited state energy. Since the system is more conjugated, the band gap is smaller and the excited state energy is smaller. Therefore, what will happen is that the excitation will move across the material and will get to the most perfectly conjugated molecules because these are the ones for which the energy of the excited state is smallest. Because they emit only from the most well conjugated molecules, the emission will be from a single species where as in absorption, you can have not only the most conjugated but also the slightly distorted molecules that will also absorb. Absorption will indicate disorder in the system much more than emission will.

	~~===~~ Simulation of Emission ~~===~~		'''Simulation of Emission'''
	[[Image:Emission_simulation_exp.png\|thumb\|300px\|Simulation of absorption. S1 relaxation energy decreases as the chain grows.]]		[[Image:Emission_simulation_exp.png\|thumb\|300px\|Simulation of absorption. S1 relaxation energy decreases as the chain grows.]]

	The theoretical data matches the experimental data.		The theoretical data matches the experimental data.
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	[[Image:Emission_simulation.png\|thumb\|400px\|Simulation of emission predicts various transition energies.]]		[[Image:Emission_simulation.png\|thumb\|400px\|Simulation of emission predicts various transition energies.]]
	In stilbene the relaxation energy is .27 eV. As ~~you increase~~ the length the relaxation comes down to .15eV. The relaxation energy as a function of 1/n shows a linear relationship. A relaxation energy of .15 eV for the S<sub>1</sub> excited state is typical for many polymers. The 0-1 is almost as large as the 0-1 transition in simulating the emission spectrum.		In stilbene the relaxation energy is .27 eV. As the length increases the relaxation comes down to .15eV. The relaxation energy as a function of 1/n shows a linear relationship. A relaxation energy of .15 eV for the S<sub>1</sub> excited state is typical for many polymers. The 0-1 is almost as large as the 0-1 transition in simulating the emission spectrum.

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Cmditradmin at 16:51, 1 September 2009

2009-09-01T16:51:14Z

Show changes

Cmditradmin: /* Vibronic Progression */

2009-09-01T16:32:13Z

Vibronic Progression

← Older revision		Revision as of 09:32, 1 September 2009
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	=== Vibronic Progression ===		=== Vibronic Progression ===

	Vibronic progression can be seen in the absorption and emission spectra. Vibronic progression means that there is a coupling to vibrational modes in ~~your~~ polymer or oligomer ~~as you have an~~ excitation from the ground state to the excited state, or emission from the excited state down to the ground state.		Vibronic progression can be seen in the absorption and emission spectra. Vibronic progression means that there is a coupling to vibrational modes in a polymer or oligomer including excitation from the ground state to the excited state, or emission from the excited state down to the ground state.

	=== Change in excited state geometry ===		=== Change in excited state geometry ===