### Slides - Department of Physics

```Physics of Excited
States in Solids
----ultrafast laser studies
and numerical modeling
----Olin 209
------Qi Li – Ph.D. student
Joel Grim – postdoc (WFU ‘12)
Yan Wang – Shanghai visiting
Keerthi Senevirathne - CEES
Burak Ucer – Research Prof.
Richard Williams – Prof.
National Lab Partners
Lawrence Berkeley National Laboratory
Lawrence Livermore National Laboratory
Pacific Northwest National Laboratory
Oak Ridge National Laboratory
Office of Defense Nuclear
Nonproliferation, Office of
Nonproliferation Research and
Development (NA-22) of the U. S.
Department of Energy under Contracts
DE-NA0001012 & DE-AC02-05CH11231.
. . . ~ 3 nm, ns duration, random location:
– not by imaging!
Particle track
Laser experiment
2Δ r ~ µm - mm
1/e
r  ?
1/e
6.1 eV
laser
Δ ≈ 40 nm
for α = 4 x 105 cm-1 (NaI)
equate e-h densities that produce the same quenching in both cases
Measuring 2nd and 3rd order quenching:
 dn 
i
 Ki n
 
 dt  NLQ
Z-scan nonlinear quenching set-up
0
0 =
ℎ
uv laser
translating lens
integrating sphere
6
0.07
excitation density (e-h/cm3)
0.3
5.8
0.3
0.07
x 1020
0.03
K2 = 1 x 10-9 cm3s-1
Quenching is 2nd order in BGO.
Excitons during NLQ.
0.06
excitation density (e-h/cm3)
0.2
3.3
0.2
0.06
x 1020
0.03
K3 = 8 x 10-31 cm6s-1
Quenching is pure 3rd order in SrI2.
Free carriers during NLQ.
Pacific Northwest
National Lab
Kinetic Monte Carlo
August 2012
Wake Forest data
We calculate “electron yield” Ye(Ei) to
compare with SLYNCI and K-dip data,
by the integral below. Feh(Ei,n0) is the
fraction of all excitations produced at
local density n0 by an electron of initial
energy Ei including all delta rays
(GEANT4). LLY(n0) is the local light
yield model of nonlinear quenching
and diffusion in Li et al JAP 2011).

K2(t)
(cm3t-1/2s-1/2)
K3
(cm6s-1)
α
(cm-1)
r0
(nm)

(cm2/Vs)

(cm2/Vs)
Value used
0.47
0.73 x 10-15
Measured
0.47
0.35
0.73 x 10-15
0
0
4 x 105
4 x 105
3
3
10
10
10-4
10-4 (STH)
Method
LY≤1-k1
z-scan
5.9 eV
z-scan
5.9 eV
thin film
expt. z-scan/K-dip
calc. NWEGRIM
photocondivity
e-pulse
STH hopping
Reference
Saint-Gobain
Dorenbos rev.
present work
present work
Martienssen
WFU, Delft
PNNL
Kubota, Brown
Popp & Murray
Cherepy et al
Alekhin et al, SCINT
LLY of Li et al JAP 2011
with K3 from z-scan
k1 = 0.04
LY ≤ (1 - k1) = 0.96
80,000 ph/MeV
Can we measure the radius of an electron track?
. . . phone conversation with Fei Gao (PNNL),
Feb. 2012
130
Non-proportional response, %
120
110
50%
100
90
80
70
60
50
40
30
NaI:Tl K-dip
20
10
0
0.01
NaI:Tl z-scan
Khodyuk et al
0.1
1
10
100
Electron energy, keV

0 =

2

0
0 =
ℎ
0 = 0.4 mJ/cm2
= 4 x 105 cm-1
ℎ = 6.1 eV
0 =1.6 x 1020 e-h/cm3
z-scan
K-dip

0

= 0 =
2
ℎ

2

=

0

ℎ

=
0.16 eh
= 64 eV/nm (Vasil’ev, 2009)
= 45 eV/nm (PNNL, 2011)
Calculated immobile STH distribution
[NWEGRIM, (PNNL) Fei Gao 2012]
eV/nm
nm3
2.5 5.5 eV/eh
= 3 nm
= 2.6 nm
= 2.8 nm
in NaI near
track end
CsI:Tl (0.3%) Induced Absorption
(d) @ ~ 0 ps
(d) @ 17 ps
0.8
0.6
(d)
0.8
0.6
0.4
(d)
0.2
0.4
0.0
0.4
0.5
0.6
0.2
0.7
0.8
0.9
1.0
energy (eV)
0.5
0.0
0.96 eV
0.5 eV
0.4
-0.2
0.9
0.8
0.7
0.6
0.5
0.3
(d)
gy
er
en
V)
(e
-2
0
2
4
6
8
time (ps)
16
10 12 14
0.2
0.1
0.0
0
5
time (ps)
10
15
1.1
Qi Li – Young Researcher Award –
International Conference on Defects in
Insulating Materials, Santa Fe, July 2012.
First principles calculations and experiment
predictions for iodine vacancy centers in SrI2
```