Physics of Excited States in Solids

-----ultrafast laser studies

and numerical modeling-----

Olin 209-------

Qi Li – Ph.D. studentJoel Grim – postdoc (WFU ‘12)Yan Wang – Shanghai visitingKeerthi Senevirathne - CEESBurak Ucer – Research Prof.Richard Williams – Prof.

National Lab PartnersLawrence Berkeley National LaboratoryLawrence Livermore National LaboratoryPacific Northwest National LaboratoryOak Ridge National Laboratory

National Nuclear Security Administration, 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

6.1 eV laser

Laser experiment

? r

2Δ r

~ µm

- m

m

1/e

1/e

for α = 4 x 105 cm-1 (NaI)

equate e-h densities that produce the same quenching in both cases

nm

6

Z-scan nonlinear quenching set-up

uv laser

PMT

integrating sphere

translating lens

Measuring 2nd and 3rd order quenching:

ii

NLQ

nKdtdn

𝑛0=𝐹0𝛼h𝑣

K2 = 1 x 10-9 cm3s-1

5.8 0.3 0.07 0.030.30.07excitation density (e-h/cm3) x 1020

Quenching is 2nd order in BGO. Excitons during NLQ.

K3 = 8 x 10-31 cm6s-1

3.3 0.2 0.06 0.030.20.06excitation density (e-h/cm3) x 1020

Quenching is pure 3rd order in SrI2. Free carriers during NLQ.

Wake Forest data

Pacific Northwest National LabKinetic Monte CarloAugust 2012

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).

  Value used Measured Method Reference0.47 0.47

0.35 LY≤1-k1 Saint-Gobain

Dorenbos rev.K2(t)

(cm3t-1/2s-1/2)0.73 x 10-15 0.73 x 10-15 z-scan

5.9 eVpresent work

K3

(cm6s-1)0 0 z-scan

5.9 eVpresent work

(cm-1)

4 x 105 4 x 105 thin film Martienssen

r0

(nm)3 3 expt. z-scan/K-dip

calc. NWEGRIMWFU, Delft

PNNL

(cm2/Vs)10 10 photocondivity

e-pulse Kubota, Brown 

Aduev

(cm2/Vs)10-4 10-4 (STH) STH hopping Popp & Murray

k1 = 0.04LY ≤ (1 - k1) = 0.96 80,000 ph/MeV

Cherepy et al

Alekhin et al, SCINT

LLY of Li et al JAP 2011with K3 from z-scan

Can we measure the radius of an electron track?

. . . phone conversation with Fei Gao (PNNL), Feb. 2012

Track radius deduced from experiment

0.01 0.1 1 10 1000

102030405060708090

100110120130

Non

-pro

porti

onal

resp

onse

, %

Electron energy, keV

50%

1.6 x 1020 e-h/cm3

𝑛0=𝐹0𝛼h𝑣𝑛0=

𝑑𝐸𝑑𝑥

𝛽𝐸𝑔𝑎𝑝𝜋 𝑟𝑁𝐿𝑄2

0.4 mJ/cm2

4 x 105 cm-1

6.1 eV

NaI:Tl K-dipKhodyuk et al

NaI:Tl z-scan

Equating e-h densities, find radius

𝐹0𝛼h𝑣 =𝑛0=

𝑑𝐸𝑑𝑥

𝛽𝐸𝑔𝑎𝑝𝜋𝑟𝑁𝐿𝑄2

in NaI near track end

z-scan K-dip

(Vasil’ev, 2009) 3 nm

(PNNL, 2011) 2.6 nm

Calculated immobile STH distribution = 2.8 nm[NWEGRIM, (PNNL) Fei Gao 2012]

CsI:Tl (0.3%) Induced Absorption

time (ps)0 5 10 15

(

d)

0.0

0.1

0.2

0.3

0.4

0.5

0.96 eV0.5 eV

energy (eV)0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

(

d)

0.0

0.2

0.4

0.6

0.8 (d) @ ~ 0 ps (d) @ 17 ps

-0.2

0.0

0.2

0.4

0.6

0.8

-2 0 2 4 6 8 10 12 14 160.5

0.60.7

0.80.9

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