PHOTOPHYSICS OF MOLECULAR MATERIALSAND SEMICONDUCTOR NANOSTRUCTURES · 2019-03-22 · METAL ORGANIC...
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PHOTOPHYSICS OF
MOLECULAR MATERIALS AND
SEMICONDUCTOR NANOSTRUCTURES
UNIVERSITÀ DEGLI STUDI MILANO-BICOCCA
OPEN DAY 28 NOVEMBRE 2018 - CORSO DI LAUREA IN SCIENZA DEI MATERIALI
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RESEARCH TOPICS: PHYSICS OF LUMINESCENT NANOMATERIALS
Semiconductor Nanostructures
Organic and Hybrid Nanoparticles and Nanotubes
Metal Quantum Clusters
Prof. F. Meinardi Prof. S. Brovelli Dr. A. Monguzzi
DIPARTIMENTO DI SCIENZA DEI MATERIALI U5
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Photon managing for Solar Technologies (DOWN and UP photon
conversion)
Luminescent Materials for Photonics and Imaging Applications
(LED, Scintillationg, Bioimaging)
RESEARCH TOPICS: APPLICATIONS
LUMINESCENT SOLAR
CONCENTRATORS
PHOTONS UPCONVERTERS
LED, OLED MATERIALS FOR PHOTONICS
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SEMICONDUCTOR NANOCRYSTALS
Cd10Se4(SePh)12(PPr3)4
Bulk CdSe
Quantum Dot
Regime
Cluster Molecule
100,000 atoms
20 nm
100 atoms
2 nm
10 nm
Nanocrystal Quantum Dots Epitaxial Quantum Dots
<10 nm
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SEMICONDUCTOR NANOCRYSTALS
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SEMICONDUCTOR NANOCRYSTALS
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SEMICONDUCTOR NANOCRYSTALS
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SEMICONDUCTOR NANOCRYSTALS
TUNABLE OPTICAL, LUMINESCENCE and MAGNETIC PROPERTIES
vs composition, size, shape and doping
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SMART WINDOWS
OPEN DAY 28 NOVEMBRE 2018 - CORSO DI LAUREA IN SCIENZA DEI MATERIALI
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HYBRID NANOMATERIALS: FLUORESCENT
METAL ORGANIC FRAMEWORKS
Optically inert MOFs = modulable porous systems• Gas storage• Molecular sensors• Chemical catalysis
Luminescent MOFs:• From ions• From Ligands
inorganic node(metal ion or metal
cluster)
organic ligand
Metal-Organic Framework
O.M. Yaghi, H.L. Li, J. Am. Chem. Soc. 1995, 117, 104010
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RECOMBINATION MECHANISMS OF
MOLECULAR EXCITONS IN MOFS
Molecular excitons migrate within the
framework reaching energetic traps
metal ion
fluo. ligand
excitation
emission
MOF
Symmetry Monoclinic
a (Å) 16.7
b (Å) 6.9
c (Å) 28.3
β 90.6
Volume (Å3) 3252
Molecules per
unit cell4
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Absorption/Photoluminescence Properties
1
𝜏𝑟𝑎𝑑= 2.88 ∙ 10−9 𝑛2
𝑃𝐿 ν 𝑑ν
𝑃𝐿(ν)ν3
𝑑νන𝜀 ν
ν𝑑ν
𝑄𝑌 =𝜏𝑒𝑥𝑝
𝜏𝑟𝑎𝑑
Stickler-Bergrelationship
Einstein Coefficients
RECOMBINATION MECHANISMS OF
MOLECULAR EXCITONS IN MOFS
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Axis R (Å) Θ2 R0 (nm) khop (THz)D (cm2s-
1)L (nm)
x 9.2 4 6.0 3.5∙101 0.30 252
y 9.0 1 4.7 9.9 8.1∙10-2 131
z' 6.0 1 4.7 1.1∙102 0.41 296
𝐷𝑖 = 𝑘ℎ𝑜𝑝𝑅2
𝑖
XRD analysis
𝑘ℎ𝑜𝑝 = 𝑘𝐹𝑠 =1
𝜏𝐷
𝑅0𝑅
6
𝑅0 = 0.211 𝜃2 ∙ 𝑛−4 ∙ 𝑄𝑌 ∙ 𝐽 λൗ1 6
𝐽 λ = න0
∞
𝑃𝐿 λ ∙ 𝜀𝐴 λ ∙ λ4 𝑑λ
Förster Rate
Förster Radius
Spectral Overlap
spectroscopy
𝐼
𝐼0= 10−𝐴 = 𝑒−𝜀𝑀𝑥
x (nm) d (nm)
MOF 924 ~100
MOF-bpy 629 ~50
MOF-dabco 564 ~200
Lambert-Beer
1. Excitation light penetration length (x)
Li = (Dit)0.5
2. Singlet diffusion length (L)
L/d >> 1
x/d >> 1
RECOMBINATION MECHANISMS OF
MOLECULAR EXCITONS IN MOFS
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ENGINEERED MOFS FOR LOW POWER
PHOTON UPCONVERSION
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METAL QUANTUM CLUSTERSBRIDGING THE GAP BETWEEN ATOMS AND COLLOIDAL NANOPARTICLES
Mn clusters combine molecule-like electronic structure with quantum confinement effects
• unmatched flexibility for tailoring their
physical properties
“magic” sizes and electro/magnetic properties are dictated by the s valence electrons of metal constituents
spherical jellium model for s electrons
𝐻 = 𝐻𝑒𝑙 + 𝐻𝑏𝑎𝑐𝑘 + 𝐻𝑒𝑙−𝑏𝑎𝑐𝑘
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ENERGY
DELOCALIZATION EXCITED AGGREGATE
FORMATION
R
Rex
Excimers exhibit the absorption spectrum of their molecular constituents and long-lived non-resonant PL
IDEAL large Stokes Shift Emitters
Molecular excimers are typically formed upon collisional interaction between monomers in concentrated solutions
In principle not realizable as stable self-standing particles, unless…
EXCIMER: Excited State Aggregate
METAL QUANTUM CLUSTERSEXCITED STATES INTERACTIONS
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• fPL = 12%, t =1.6 ns
trad =13.3 ns
[trad (SB) =12 ns]
• Mirror symmetry PL, distinct
vibronic replica
• No LM-CT emission @ 2 eV
• fPL = 4.5%, ultra-slow decay
• No LM-CT @ 2 eV
Au8 absorption/PLE
Largely Stokes Shifted PL
• Au8 absorption/PLE
D
o
u
b
l
e
encapsulated single clusters
[Molecular photophysics]
Au8-pX
Stokes shift 0.93 eV
Ab
s/P
LE
Ab
s/P
LE
METAL QUANTUM CLUSTERSEXCITED STATES INTERACTIONS
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METAL QUANTUM CLUSTERSMANIPULATING SECONDARY INTERACITONS FOR BIOIMAGING
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SPECTROSCPY LAB
CW and TR ultrafast photoluminescence spectroscopy
Close cycle cryostat T ~ 1.5 K
Magnetic Field Response ( fino a 5.5 T )
Confocal imaging micro-photoluminescence