Collaborations - members.femto-st.frmembers.femto-st.fr/sites/femto-st.fr.laurent_larger/files/content/Homepage_ll... · Collaborations M. DeVittorio J.P. Hermier. Outline Introduction

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