Interazione Radiazione Materia

1
SiO2 Advanced Dielectrics and Related Devices
Inhomogeneity of Oxygen Deficient Centers in
silica probed by nanosecond Time-Resolved
Luminescence measurements
Michele DAmico1,2, Fabrizio Messina1, Marco
Cannas1, Maurizio Leone1,2 and Roberto Boscaino1
1Dip. di Scienze Fisiche ed Astronomiche -
Università degli Studi di Palermo 2Istituto di
Biofisica - Consiglio Nazionale delle Ricerche
Palermo - Italy
S. Etienne, 1st July, 2008
2
Introduction
Glass
Crystal
Point defects in different environments
Identical Point defects
Homogeneous lineshape
Inhomogeneous broadening
Homogeneous lineshape

How to distinguish and estimate the two
contributions to total linewidth?
3
Materials
Glass
Crystal
Fused quartz silica (SiO2) Infrasil 301 (Heraeus)
Electron irradiated Lithium Fluoride (LiF)
Ge-ODC(II)
F3 centers
Two coordinated Germanium atom
3 anion vacancies with 2 electrons
with 1 ppm Ge atoms
4
Time resolved luminescence experimental setup
Pulse n
Pulse 3
Pulse 1
Pulse 2
Luminescence
Time (ns)
Pulsed tunable laser Vibrant OPOTEK
CCD air cooled detector PIMAX PI-Acton
5 ns temporal width 10 Hz Repetition Rate 0.3
mJ/cm2 per pulse
2 nm spectral width 1 ns temporal resolution -20
C working temperature
5
Time Resolved Luminescence of Ge-ODC(II)
S1 ? S0 Transition
a)
Contour Plot of normalized intensity
T25 K (Only radiative decay)
Eex5 eV
(S0 ? S1 Transition)
6
Time Resolved Luminescence of Ge-ODC(II)
and F3
Lineshape first moment
Single exponential decay lifetime
Analogous PL measurements were performed on
crystal sample
7
Experimental Results
Why?
8
Homogeneous ensemble of point defects in a crystal
Identical defects
Homogeneous PL band
Lifetimes measured at different emission energies
give the same value
9
Inhomogeneous system point defects in a glass
Inhomogeneous PL band
Different defects
Each sub-bands has a different lifetime
10
Homogeneous and inhomogeneous width comparable
t0
t
11
Point defects in a crystal Standard Background

• Configuration Coordinate Model
• Born-Oppenheimer Approximation
• Harmonic Approximation
• Franck-Condon Principle
• Electron-Phonon Coupling with a single
  vibrational mode of energy Ep

Homogeneous PL lineshape
12
Our hypothesis about Inhomogeneity effects in
Silica Gaussian distribution of Zero Phonon Line
E0
13

• Simultaneous fitting of
• PL lineshape
• Kinetics of first moment
• Lifetimes dispesion

Silica
Crystal
14
Fitting results
DAmico et al, Phys. Rev. B, In press (2008)
arXiv0805.4507v1
15
Time resolved PL of Ge-ODC(II) and F3 centers
16
Acknowledgements
Thanks to Dr. Rosa Maria Montereali for have
kindly supplied the LiF sample
Thanks to LAMP research group for very useful
discussions
Laboratory of Amorphous Material Physics
17
Thank you for the attention!!
_at_ damico_at_fisica.unipa.it
http// www.fisica.unipa.it/amorphous/
18
Poor dependence from Excitation energy
19
Comparison between Ge-doped and fused silica
20
Absorption Cross Section
Mirror simmetry
(Spectral side)
(Temporal side)
Forster equation
Poissonian shape