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 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

1/e

Laser experiment

1/e

6.1 eV laser



r

 ?

Δ𝑧 ≈ 40 nm for α = 4 x 10 5 cm -1 (NaI)

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

Measuring 2 nd and 3 rd order quenching:

dn dt NLQ

Z-scan nonlinear quenching set-up

 

K i n i

𝑛 0 = 𝐹 0 𝛼 ℎ𝑣

uv laser translating lens

0.07

excitation density (e-h/cm 3 ) 0.3

5.8

0.3

0.07

0.03

x 10 20 K 2 = 1 x 10 -9 cm 3 s -1

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

0.06

excitation density (e-h/cm 3 ) 0.2

3.3

0.2

0.06

0.03

x 10 20 K 3 = 8 x 10 -31 cm 6 s -1

Quenching is pure 3 rd order in SrI 2 . Free carriers during NLQ.

Pacific Northwest National Lab Kinetic Monte Carlo August 2012 Wake Forest data

We calculate “electron yield” Y

e (E i

) to compare with SLYNCI and K-dip data, by the integral below. F

eh (E i ,n 0

) is the fraction of all excitations produced at local density n

0

energy E

i

by an electron of initial including all delta rays (GEANT4). LLY(n

0

) is the local light yield model of nonlinear quenching and diffusion in Li et al JAP 2011).

𝑲 𝟏

K 2 (t) (cm 3 t -1/2 s -1/2 ) K 3 (cm 6 s -1 )

α 𝜶

(cm -1 ) r 0 (nm)

𝝁 𝒆

(cm 2 /Vs)

𝝁 𝒉

(cm 2 /Vs) Value used

0.47

0.73 x 10 -15 0 4 x 10 5 3 10 10 -4

Measured

0.47

0.35

0.73 x 10 -15 0 4 x 10 5 3 10 10 -4 (STH)

Method

LY≤1-k 1 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 Aduev Popp & Murray

Cherepy et al Alekhin et al, SCINT LLY of Li et al JAP 2011 with K 3 from z-scan k1 = 0.04

LY ≤ (1 - k

1

) = 0.96 80,000 ph/MeV

Can we measure the radius of an electron track?

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

Track radius deduced from experiment

130 120 110 100 90 80 70 60 50 40 30 20 10 0 0.01

NaI:Tl K-dip

Khodyuk et al 100 50%

NaI:Tl z-scan

0.1

1 10 Electron energy, keV 𝑛 0 = 𝛽𝐸 𝑑𝐸 𝑔𝑎𝑝 𝑑𝑥 𝜋𝑟 2 𝑁𝐿𝑄 𝑛 0 = 𝐹 0 𝛼 ℎ𝑣 𝐹 0 = 0.4 mJ/cm 2 𝛼 = 4 x 10 5 cm -1 ℎ𝑣 = 6.1 eV 𝑛 0 = 1.6 x 10 20 e-h/cm 3

Equating e-h densities, find radius

z-scan K-dip 𝐹 0 𝛼 ℎ𝑣 = 𝑛 0 = 𝛽𝐸 𝑑𝐸 𝑔𝑎𝑝 𝑑𝑥 𝜋𝑟 2 𝑁𝐿𝑄 𝑟 2 𝑁𝐿𝑄 = 𝜋 𝑑𝐸 𝑑𝑥 𝐼 0 𝛼 ℎ𝑣 𝛽𝐸 𝑔𝑎𝑝 = 𝜋 0.16

𝑑𝐸 𝑑𝑥 eV/nm eh nm3 2.5 5.5 eV/eh 𝑑𝐸 𝑑𝑥 = 64 eV/nm (Vasil’ev, 2009) 𝒓 𝑵𝑳𝑸 =

3 nm

𝑑𝐸 𝑑𝑥 = 45 eV/nm (PNNL, 2011) 𝒓 𝑵𝑳𝑸 =

2.6 nm

Calculated immobile STH distribution [NWEGRIM, (PNNL) Fei Gao 2012] 𝒓 𝑺𝑻𝑯

= 2.8 nm

in NaI near track end

0.8

CsI:Tl (0.3%) Induced Absorption

0.8

 (  d) @ ~ 0 ps  (  d) @ 17 ps 0.6

0.4

0.6

0.2

0.4

0.2

0.0

ene -0.2

rgy 0.9

(e 0.8

0.7

V) 0.6

0.5

-2 0 2 4 6 8 10 12 14 16 time (ps) 0.0

0.5

0.4

0.3

0.2

0.1

0.0

0.4

0.5

0.6

0.7

0.8

energy (eV)

0.9

1.0

1.1

0.96 eV 0.5 eV 0 5

time (ps)

10 15

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 SrI 2