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W/Biophysics > 11.12 Luminescence and laser > Flashcards

11.12 Luminescence and laser Flashcards

1
Q

What is luminescence?

A

Spontaneous emission of a photon due to relaxation of an excited electron

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2
Q

Fluorescence lifetime

A

10^(-10) - 10^(-7) seconds

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3
Q

Phosphorescence lifetime

A

10^(-5) - 10s

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4
Q

What is molecular vibration?

A

change in shape, stretching, bending of a molecule

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5
Q

What does the Jablonski diagram illustrate?

A

transitions between electronic states of molecules

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6
Q

What is spin multiplicity?

A

number of possible orientations of the spin angular momentum

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7
Q

What is emitted / released in vibrational relaxation?

A

heat, NO PHOTON RELEASED

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8
Q

What is intersystem crossing?

A

transition between two electronic states : from singlet to triplet state. Radiation-less process

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9
Q

Which has more energy? Fluorescence or phosphorescence?

A

Fluorescence

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10
Q

What is Kasha’s rule?

A

The excited molecule first reaches the lowest vibrational level of S1 and photon emission always occurs from this state to any vibrational level of the ground S0 state

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11
Q

What is Stoke’s rule?

A

Wavelength of emitted light is almost always longer than that of the excitation photon due to loss of E via heat

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12
Q

What is the stoke-shift?

A

Difference in the luminescence spectrum between aborbed and emitted wavelengths due to loss of energy as heat

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13
Q

What is the quantum yield?

A

measure of efficiency of emission : number of photons emitted / number of photons absorbed

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14
Q

What is the lifetime of luminescence?

A

decay of emitted luminescence

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15
Q

How do you calculate lifetime of fluorescence?

A

τ = 1/(Kf+Knr)
τ : lifetime
Kf : rate of photon producing transitions
Knr : rate of non-radiating transitions

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16
Q

What is the function of a fluorescence spectrometer?

A

analyses fluorescence properties of a sample to determine the concentration of an analyte in solution

17
Q

What does FRET stand for?

A

Fluorescence resonance energy transfer

18
Q

What is FRET used for?

A

To measure distance and detect molecular interactions between organisms

19
Q

What is the process used in FRET?

A

energy transfer from donor to acceptor without emission, thanks to dipole-dipole interactions

20
Q

What does FRAP stand for?

A

fluorescence recovery after photobleaching

21
Q

What is photobleaching?

A

photochemical alteration of a dye or fluorescent molecule - permanently unable to emit fluorescence

22
Q

What is a dichroic mirror?

A

mirror that lets only a small range of light pass through and reflects the rest

23
Q

What is induced emission?

A

emission is induced by an incoming photon : incoming radiation is amplified (since they have same phase, constructive interference)

24
Q

What is a coherent process?

A

a process is coherent if the difference of their phase is constant or changes in a regular way

25
Q

What does LASER stand for?

A

light amplification by stimulated emission of radiation

26
Q

What does the optical resonator ensure?

A

ensures positive feedback and choice of frequency corresponding to the resonance

27
Q

What is the condition for laser resonance?

A

2L = m * lamda

m : integer

28
Q

What does the frequency of the laser depend on?

A

On the spectral properties of the mirror and the length between mirrors

29
Q

What are the 6 properties of laser light

A
  1. small divergence : parallel beam
  2. Large power
  3. Small spectral bandwidth (monochromatic)
  4. Often polarized
  5. Possibility of short pulses (ps, fs)
  6. Coherence
30
Q

What is coherent length?

A

largest distance at which interference can still be observed (large for lasers) bc close emission points

31
Q

What are 4 types of lasers?

A
  1. Solid state laser
  2. Gas laser (Co2)
  3. Dye laser (coumarine)
  4. semiconductor (diode) laser
32
Q

What is a solid state laser?

A

Laser that uses solid medium instead of a liquid or gas one. For example neodymium-YAG laser

33
Q

2 examples of gas lasers

A

CO2, HeNe

34
Q

2 examples of dye laser

A

coumarine, rhoatamine

W/Biophysics (24 decks)

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