Collaborations -...
Transcript of Collaborations -...
Selective control of blinking and polarization of single photon emission in colloidal nanocrystals
Alberto Bramati
Collaborations
M. DeVittorio
J.P. Hermier
Outline
IntroductionSingle Photon EmissionSuppression of blinkingPolarized single photonsPerspectives: coupling with
nanocavities
Quantum emitters for single photon generation
Single atomKimble et al. PRL (1977)Hennrich et al New Journal of Physics (2004)
Single nitrogen vacancy in diamondH. Weinfurter et al. PRL (2000)P. Grangier et al. Optics Letters (2000)
Single Molecule at room temperatureB. Lounis and W.E. Moerner, Nature (2000)
Single Quantum DotArakawa et al. Nature Materials 5, 887 (2006)
Single Quantum Dot in PhC cavitiesImamoglu et al. Nature 445, 896 (2007)
Colloidal semiconductor nanocrystals
Wet- chemistry synthesis bright, stable, well controlled with tunable wavelength
optoelectronics (LEDs, lasers, solar cells…)biology (fluorescent markers)quantum optics (single emitters)
Core (~1000 atoms)
Passivation Shell (some nm)
Strong confinement: Photon antibunching observed at room temperature
3 nm1 nm
Nanocrystals drawbacks
Blinking Spectral Diffusion Not polarized emission
Wav
elen
gth
Time window (8 sec)
R. G. Neuhause et al., Phys. Rev. Lett. 85, 3301 (2000).X Brokmann et al., New journal of physics 6, 99 (2004).
Shell
Core
Nanocrystals drawbacks: solutions
Blinking suppression with giant shells
Loss of the antibunching behavior
Polarized emission with rods
Jiangtao Hu et al. Science 292, 2060 (2001)
B. N. Pal et al. Nano Lett., 2012, 12 (1)
B. Malher et al., Nature Mat. 7, 659 (2008).
Colloidal dot in rod
Carbone et al., Nano Letters 7, 2942 (2007).
CdSe
CdS
TEM images of a typical synthesis output
Pulsed excitation
50ps@404nm
BG ~600nm
Efficient Auger Recombination
)()(
)()(),()2(
ττ
τ+
+=
tItI
tItItg
Electronic structures
Type I NCs Type II NCs
core coreshell shell
CdSe/CdS
CdSe CdS
CdSe/ZnS
CdSe ZnS
Electronic structures of different types of spherical NCs. What about Dots-in-Rod ?
Localization/delocalization of electrons: large core
Big cores : the electrons are localized inside
Localisation/delocalization of electrons: small core
Small cores : the electrons are delocalized in the shell
Localization/delocalization of electrons
Type I NCsQuasi-Type II NCs
Core diameter
Electron Localization
Auger Effect
Big cores : localized electrons
Small cores : delocalized electrons
Single photon behavior vs rod length
Quasi-Typ
e II
Single photon behavior vs rod length
Quasi-Typ
e II
Single photon behavior vs rod length
Quasi-Typ
e II
Shell length and neutral Auger effect
Multiphoton Emission Probability
Shell length
Efficiency of the neutral Auger effect
l=22nm l= 58 nm
g(2)<0,2 g(2)≤0,5
Blinking (spherical NCs)
Standard NCs CdSe/ZnS
Giant NCs CdSe/CdS
P≈1/τμ
Off Times Probability : Poff(t>toff) ?
μ=0.73<1
μ=2.3>2
Spherical nanocrystals
Heavy Tailed Law
Off Times Probability Distribution: thin shell
Above saturation :
100
101
10-4
10-3
10-2
10-1
100
Poff
(τoff
>τ )
τ (ms)
Dark noise
μ=2.65
τ (ms)τ (ms)100 101
μ=2.65
10-1
10-2
10-3
10-4
10-0
τ (ms)
Above saturation :
Dark noise
Off Times Probability Distribution: thick shell
OFF States Probability Distribution
Blinking, Grey States and Trion
Strong reduction of blinking
What about the Quantum Efficiency of the grey state?
Grey state
OFF state
Quantum efficiency of ionized dots-in rods is comparable to that of neutral ones
P Spinicelli et al. PRL. 102, 136801 (2009)
Spherical NCs CdSe/CdS
Blinking, Grey States and Trion
Blinking vs thickness
Shell thickness
t=4nm
t=7nm
Blinking
µ≈1
µ>2
Efficiency of Trion Auger recombination
Rod Geometry and emission properties
s=(t-d)/2
Constant length l=22nm Constant thickness t=7nm
F. Pisanello et al., Advanced Materials (2013)
Linearly polarized single photon emission
Core diameter d=2.7nmShell thickness t=7nm
Rod length l=22nm
d=2.7nmt=7nml=35nm
d=2.7nmt=4.5nml=50nm
Degree of linear polarization:
δ=35%
δ=55% δ=80%
Polarization Degree > 50%
1D Dipole
Defocused microscopy: Radiation diagramm
Focused imageDefocused image for dipole
like emitter
X. Brokmann et al., Chem. Phys. Lett. 406, 210 (2005).
F. Pisanello et al., Appl. Phys. Lett. 96, 033101 (2010) L. Carbone et al., Nano Lett. 7, 2942 (2007)
Back
Sca
tter
ing
Phot
olum
ines
cenc
e
Defocused microscopy: Radiation diagram
c
500 550 600 650 700 750
0
20
40
60
80
100
Ref
lect
ance
(%
)
Wavelength (nm)
PL
inte
nsity
(A.U
.)
FWHM ~13nm
Nanocrystal in DBR cavity
Nanocrystal in DBR cavity
PL spectrum: line narrowing
PL decay of free-space
nanocrystals τ fs ~ 23 ns
PL decay of curve of single
nanocrystal in cavity: τcav ~ 9 ns
A. Qualtieri et al., New J. Phys 11, 033025 (2009).
Antibunching
Colloidal nanocrystals in a PhC cavity
Q~600
A. Qualtieri, F. Pisanello et al., Microel. Eng. 87, 1435 (2010)
Coupling NC with a parabolic mirror
-Parabolic mirror-Already used for single
atoms, to be extended to nanocrystals
Efficient collection of photons radiated by NC and efficient coupling of NC and light field
First steps taken: mounting of nanocrystals in the structure
Collaboration MPL/LKB
Conclusions
Dot-in-rod nanocrystals: efficient single photon sources
Strongly reduced blinking with thick shells; strong antibunching preserved
Strong polarized emission and dipole-like radiation pattern
Spontaneous emission rate enhanced by coupling with 2D photonic crystal nanocavities
PhD Students: R. Hivet V.G. Sala T. BoulierM. ManceauS. Vezzoli
The team
Post-Doc E.Cancellieri
Permanent Staff: Elisabeth Giacobino, Alberto Bramati
Former members: M. RomanelliC. Leyder J. Lefrère C. AdradosF. PisanelloG. Leménager
A. Amo