The crystal field effect and vibronic coupling
Structure of the free ions into fine structure
terms defined by the quantum numbers L,
The energy levels of the dopant ion can be
S, J (denoted in spectroscopic notation as
shifted by
2S+1LJ). The crystal fie
e additional energy correction:
E g ep LO ,
This means a reduction in the band gap
by the amount.
The radius, rp, which 1specifies how far the
2
extends. If ep is small:
rp
lattice distortionm .
2
LO
10.5.1 General principles of inelastic
light scatteri
9
Phonons
9.1Infraredactivephonons
9.2Infraredreflectivityandabsorption
inpolarsolids
9.3Polaritons
9.4Polarons
9.5Inelasticlightscattering
9.6Phononlifetimes
10.1 Infrared active phonons
The resonant frequencies of the
phonons occur in the infrared
spect
Phase matching
P
( 2)
0 E (t )
2
Optical frequency conversion
(Second Harmonic generation)
Energy conservation
Momentum conservation
= 2 - 21=
0
k = k2 -2k 1 = 0
Birefringence Phase Match (BPM)
k
Z
Lp
Ln
Y
Lp+Ln
X
dij
X
d ( x ) d 33 K m e iGm x
m
Gm
2
10
NonlinearOptics
Nonlinear susceptibility tensor
D 0 E P 0 r E
P 0 E
r 1
non
(1)
( 2) 2
( 3) 3
P 0 ( E E E .) P (1) P ( 2) P (3) .
non
r
(1)
( 2)
( 3)
2
1 E E .
Pi ( 2 ) 0
(2
ijk) E j Ek
j , k x , y , z
Pi ( 3) 0
( 3)
ijkl E j Ek El
j , k ,l x , y
1 Free carrier reflectivity and absorption
Assume the system is lightly damped,
0, 0, 1, zero reflectivity
r
opt
2
2
occurs ata
frequency given by:
p
processes with a single frequencyindependent scattering time deduced
from the DC conductivity.
opt 1
B
9
Luminescence
centres
9.1Vibronicabsorptionandemission
9.2Colourcentres
7.3Paramagnetricimpuritiesinioniccrystals
7.4Solidstatelaserandopticalamplifiers
7.5Phosphors
9.1 vibronic absorption and emission
Continuous vibronic bands: the
electronic states ar
7
Free electrons
7.1Plasmareflectivity
7.2Freecarrierconductivity
7.3Metals
7.4Dopedsemiconductor
7.5Plasmons
2
p
Plasma: A neutral gas of heavy ions
r () 1
,
2
( i
)
and light electrons. Metals and doped
1
semiconductors can be treated as
2
Ne 2
where
5
5.1
5.2
5.3
5.4
Luminescence
Light emission in solids
Interband luminescence
Photoluminescence
Electroluminescence
5.1 Light emission in solids
The
he reverse process of absorption emission spontaneous emission rate for a two level:
mission in solids is
3.4 Photoluminescence spectroscopy
Photoluminescence (PL) spectra:
The sample is excited with a laser or lamp with
photon energy greater than the band gap. The
spectrum is obtained by recording the emission as a
function of wavelength.
Photoluminescence e
6.5 Optical emission
The use of quantum well structure in
EL devices is their main
commercial application:
1. A greater range of emission
wavelength;
I ( h ) M g ( h )
2. An enhancement of device
h E
.
( h E ) exp
efficiency.
k T
Zn0.8Cd0.2Se/ZnSe is a
3.3.4 The frequency dependence of the band edge absorption
2
2
( ) Wi f
M g ( h).
h
g ( ) 0
for E g ,
3
2
1
1 2
g ( ) 2 ( E g ) 2
2
for E g .
For E g , ( ) 0.
1
2
For E g , ( ) ( E g ) .
Frequency dependence approximately obeyed
The coulomb attraction
4.4 Free excitons at high densities
The laser can create excitons in the sample with a density that is proportional to laser power.
Mott density at which exciton wave function
overlap occurs:
N Mott
1
4
rn3
3
NMott=1.11023m-3 for GaAs, n=1. This is
easil
4
4.1
4.2
4.3
4.4
4.5
Excitons
The concept of excitons
Free excitons
Free excitons in external fields
Free excitons at high densities
Frenkel excitons
4.1 The concept of excitons
Exciton: bound electron hole pair
Two basic types:
Wannier Matt excitons (fr
2.2 The dipole oscillator model
2.2.4 Local field correction
The actually atomic dipoles respond not
only to the external field, but also to the
field generated by all the other dipoles
Elocal E Eother
Eother
dipoles
dipoles
,
P
,
3 0
P
Elocal E
3 0
P N
3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
Interband
absorption
Interband transitions
The transition rate for direct absorption
Band edge absorption in direct gap semiconductors
Band edge absorption in indirect gap semiconductors
Interband absorption above the band ed
2
2.1
2.2
2.3
3.4
Classical propagation
Propagation of light in a dense optical medium
The dipole oscillator model
Dispersion
Optical anisotropy: birefringence
Chapter 2 Classical propagation
E ( z , t ) E0 e i ( k z t ) ,
k (n i) / c
E0 e z e i ( nz / c
1.4 Optical materials
1.4.2 Glass
Most types of glasses are made of silica (SiO2) with other chemicals. Insulator, all the
characteristic features crystalline insulators, the trans range from around 200 nm to
beyond 2000 nm;
Small absorption and scatterin