1
PHYS 6715 - Lecture VI
1
Lecture VI
Fluorescence
1.
Introduction
2.
Spectroscopy measurements
3.
Time-domain measurements
PHYS 6715 - Lecture VI
2
VI-1
Introduction
energy
1
4
3
2
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
⋅
=
Δ
2
2
2
0
4
1
1
8
f
i
n
n
h
me
E
ε
13.7 eV = 91 nm
outer shell: n>1
Electronic transitions
PHYS 6715 - Lecture VI
3
VI-1
Introduction
energy
ω
=
=
Δ
+
→
:
levels
oscillator
1
n
n
E
r
0
r
r
A
5
.
0
0
±
≈
−
r
r
eV
5
≈
U
14
2.5
10
rad/sec
k m
ω
→
=
=
×
Representative values:
2
2
J/m
10
6
~
×
→
k
(
)
2
0
2
1
r
r
k
U
−
≈
m
6
μ
λ
=
6 amu (2 carbon nuclei)
m
=
mid-IR
Vibrational transitions
PHYS 6715 - Lecture VI
4
VI-1
Introduction
2
1
2
J
J
E
J
mr
→
+
Δ
=
⋅
=
0.1
r
nm
=
eV
10
2
3
−
×
≈
6 amu
m
=
microwave regime
Representative values:
mm
5
.
0
1
0
≈
→
λ
Rotational transitions
(J: quantum # of
angular momentum)
PHYS 6715 - Lecture VI
5
VI-1
Introduction
Absorption spectrum
DNA
electronic
vibrational
rotational
PHYS 6715 - Lecture VI
6
VI-1
Introduction
Fluorescence
•
Luminescence is defined as light emission from systems at electronically
excited states due to optical excitation with shorter wavelength.
•
Luminescence can be classified as either fluorescence or
phosphorescence.
•
Fluorescence = luminescence due to electronic transition from singlet
excited states. The relaxation times are short, 1~10ns, because large
probability of transition to the singlet ground state.
•
Phosphorescence = luminescence due to electronic transition from triplet
excited states. The relaxation times are long, >~1ms, because small
probability of transition to the singlet ground state.

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