320
10 Recombination
(a)
2.0
2.2
2.4
2.6
600
650
550
500
450
ZnO
2.8
-1
-2
-3
-4
-5
-6
-7
-8
-9
(b)
Fig. 10.20 a Luminescence spectrum of ZnO in the visible. The arrow denotes the zero-phonon line at 2.8590 eV. The
numbers of the phonon replica are labeled. Adapted from [996]. b Luminescence spectra (solid lines) of a ZnO bulk
crystal before (‘untreated’) and after annealing in O 2 atmosphere at T = 1073 K. After annealing in Zn atmosphere at
the same temperature, the green band disappears again (dashed line). From [997]
S =
C δq
2
2 ph
,
(10.36)
where C is the ‘spring constant’ of the parabola, C = d
2 E/dq
2 .
For small S 1, we are in the weak coupling regime and the zero-phonon line is the strongest. In
the strong coupling regime, S > 1, the maximum is (red-) shifted from the zero-phonon line. We note
that in absorption, phonon replica occur on the high-energy side of the zero-phonon absorption. For
large S the peak intensities are close to a Gaussian. The correspondence of emission and absorption is
nicely seen for excitons on isoelectronic oxygen traps in ZnTe [1001]. The oxygen is on substitutional
Te site. Up to seven phonon replica are visible in Fig. 10.22 around the zero-phonon or A-line with a
(a)
q 0 q 1
E 0
q
E
E 1
h
h
S
E
(b)
ZPL
absorption
S=
0
E
2
1
4
8
emission
Fig. 10.21 a Configuration diagram of two states that differ in their configuration coordinate by δq = q 1 − q 0 . Both
are coupled to phonons of energy The absorption maximum (solid vertical line) and emission maximum (dashed
vertical line) are shifted with respect to the zero-phonon line (dotted vertical line) with energy E 1 − E 0 . The Huang–Rhys
parameter is S ∼ 4. (b) Intensity of zero-phonon line (‘ZPL’) and phonon replica (10.35) for emission and absorption
processes with different values of the Huang–Rhys parameter S as labeled
10 Recombination
(a)
2.0
2.2
2.4
2.6
600
650
550
500
450
ZnO
2.8
-1
-2
-3
-4
-5
-6
-7
-8
-9
(b)
Fig. 10.20 a Luminescence spectrum of ZnO in the visible. The arrow denotes the zero-phonon line at 2.8590 eV. The
numbers of the phonon replica are labeled. Adapted from [996]. b Luminescence spectra (solid lines) of a ZnO bulk
crystal before (‘untreated’) and after annealing in O 2 atmosphere at T = 1073 K. After annealing in Zn atmosphere at
the same temperature, the green band disappears again (dashed line). From [997]
S =
C δq
2
2 ph
,
(10.36)
where C is the ‘spring constant’ of the parabola, C = d
2 E/dq
2 .
For small S 1, we are in the weak coupling regime and the zero-phonon line is the strongest. In
the strong coupling regime, S > 1, the maximum is (red-) shifted from the zero-phonon line. We note
that in absorption, phonon replica occur on the high-energy side of the zero-phonon absorption. For
large S the peak intensities are close to a Gaussian. The correspondence of emission and absorption is
nicely seen for excitons on isoelectronic oxygen traps in ZnTe [1001]. The oxygen is on substitutional
Te site. Up to seven phonon replica are visible in Fig. 10.22 around the zero-phonon or A-line with a
(a)
q 0 q 1
E 0
q
E
E 1
h
h
S
E
(b)
ZPL
absorption
S=
0
E
2
1
4
8
emission
Fig. 10.21 a Configuration diagram of two states that differ in their configuration coordinate by δq = q 1 − q 0 . Both
are coupled to phonons of energy The absorption maximum (solid vertical line) and emission maximum (dashed
vertical line) are shifted with respect to the zero-phonon line (dotted vertical line) with energy E 1 − E 0 . The Huang–Rhys
parameter is S ∼ 4. (b) Intensity of zero-phonon line (‘ZPL’) and phonon replica (10.35) for emission and absorption
processes with different values of the Huang–Rhys parameter S as labeled