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
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
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
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
SEMICONDUCTOR NANOCRYSTALS
SEMICONDUCTOR NANOCRYSTALS
SEMICONDUCTOR NANOCRYSTALS
SEMICONDUCTOR NANOCRYSTALS
TUNABLE OPTICAL, LUMINESCENCE and MAGNETIC PROPERTIES
vs composition, size, shape and doping
SMART WINDOWS
OPEN DAY 28 NOVEMBRE 2018 - CORSO DI LAUREA IN SCIENZA DEI MATERIALI
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
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
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
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
ENGINEERED MOFS FOR LOW POWER
PHOTON UPCONVERSION
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
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
• 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
METAL QUANTUM CLUSTERSMANIPULATING SECONDARY INTERACITONS FOR BIOIMAGING
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