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http://bp.snu.ac.kr 1
Byungwoo Park
Department of Materials Science and EngineeringSeoul National University
http://bp.snu.ac.kr
White LEDWhite LEDWhite LEDWhite LED
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White LED Dae-Ryong
First Report on Electroluminescence (First LED)
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1907 First report on LED
1955 GaAs LED (infrared emission)
1962 First practical visible-spectrum LED (General Electric)
1993 Blue LED based on InGaN (Shuji Nakamura, Nichia)
1996 First commercial white LED (Nichia)
The development of LED technology has caused the efficiency and light outputto increase exponentially, with a doubling approximately every 36 monthssince the 1960s, in a way similar to Moore's law.
White LED Jongmin
History of LED
3http://bp.snu.ac.kr
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White LED Dae-Ryong
History of LED (Applications)
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Applications of LED
LCD BacklightLCD Backlight
Samsung ElectronicsSamsung Electronics
IlluminationIllumination
ElectimesElectimes
White LEDWhite LED
LEDshopLEDshop
IlluminationIllumination
Lucevista 2007 in SeoulLucevista 2007 in Seoul
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White LED Jongmin 6http://bp.snu.ac.kr
2007. 02
Applications of LED
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2007. 02
White LED Jongmin
Growth Rates
7http://bp.snu.ac.kr
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www.research.ibm.com
White LED Jongmin
Progress in Luminous Efficiency of LEDs
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Electron-Hole Recombination of p-n Junction
C. KittelIntroduction toSolid State Physics
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Double Heterostructure Injection Laser
C. KittelIntroduction toSolid State Physics
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White LED Dae-Ryong
Homojunction and Double Heterojunction
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è Confinement of carriers in the active region of double heterostructure (DH).
è High carrier concentration in the active region of DH.
White LED Dae-Ryong
Double Heterostructure
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White LED Dae-Ryong
Multi Quantum Well Structure
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White LED Jongmin
Structures of InGaN LED
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è However, these structures are not practical. - High cost!!
White LED Dae-Ryong
Trapped Light Problem
15http://bp.snu.ac.kr
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White LED Dae-Ryong
Truncated Inverted Pyramid (TIP) LED
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Ecole Polytechnique
White LED Jongmin
Structures of OLED
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White LED Devices
- Nichia High-Power LED- UV LED & RGB Phosphor
White Light
InGaN LED
RGB Light
UV Light
Downconversion(Phosphor)
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Color Wavelength Wavenumber Energy
Ultraviolet < 390 nm > 1.61×10-2 nm-1 > 3.18 eV
Violet 390 – 455 nm 1.61 - 1.38×10-2 nm-1 3.18 - 2.73 eV
Blue 455 – 490 nm 1.38 - 1.28×10-2 nm-1 2.73 - 2.53 eV
Cyan 490 – 510 nm 1.28 - 1.23×10-2 nm-1 2.53 - 2.43 eV
Green 515 – 570 nm 1.23 - 1.10×10-2 nm-1 2.43 - 2.18 eV
Color Wavelength Wavenumber Energy
Yellow 570 – 600 nm 1.10 - 1.05×10-2 nm-1 2.18 - 2.07 eV
Amber 590 – 600 nm 1.06 - 1.05×10-2 nm-1 2.10 - 2.07 eV
Orange 600 – 625 nm 1.05 - 1.01×10-2 nm-1 2.07 - 1.98 eV
Red 625 – 720 nm 1.01×10-2 - 8.73×10-3 nm-1 1.98 - 1.72 eV
Infrared > 720 nm < 8.73×10-3 nm-1 < 1.72 eV
Color Wavelength Wavenumber Energy
Blue ~460 nm ~1.37×10-2 nm-1 ~2.70 eV
Green ~525 nm ~1.20×10-2 nm-1 ~2.36 eV
Red ~670 nm ~9.38×10-3 nm-1 ~1.83 eV
White LED Jongmin
Color and Energy
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Cones: provide color sensitivity
Rods: color insensitive
White LED Dae-Ryong
Human Vision
20http://bp.snu.ac.kr
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• Definition of Lumen: Green light (555 nm) with power of 1 W has luminous flux 683 lm
• Among LEDs with same output power, green LEDs are brightest
White LED Jongmin
Eye Sensitivity Function and Luminous Efficiency
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CIE = COMMISSION INTERNATIONALE DE L'ECLAIRAGE = INTERNATIONAL COMMISSION ON ILLUMINATION
White LED Dae-Ryong
CIE Color Triangle
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E. F. ShubertLight Emitting Diodes
White LED Jongmin
Color Gamut and Color Mixing
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Temperature of Sun: ∼6000 K
White LED Jongmin
Black-Body Radiation
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White LED Dae-Ryong
White LEDs
25http://bp.snu.ac.kr
Phosphor based approaches: color stability
LED-Based Approaches
Phosphor-Based Approaches
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White LED Dae-Ryong
Dichromatic LED
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micro.magnet.fsu.edu
InGaN LED (blue) + YAG Phosphor (yellow)
White LED Jongmin
Phosphor-Based White LED
27http://bp.snu.ac.kr
- 2009-11-17
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è The thickness of the phosphor-containing epoxy and the concentration of the phosphor
suspended in the epoxy determine the relative strengths of the two emission bands.
White LED Dae-Ryong
Phosphor-Based White LED
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White LED Dae-Ryong
Photon-Recycling Semiconductor LED
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The phenomenon in which electronic states of solids are excited by some energy from an external source, and the excitation energy is released as light.
Luminescence is light not generated by high temperatures alone. It is different from incandescence, in that it usually occurs at low temperatures.
White LED Dae-Ryong
Luminescence
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Thomas Jüstel’s Group, Philips Research Laboratories Angew. Chem. Int. Ed. (1998).
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ØAbsorption (Excitation)
Ø Energy Transfer (Relaxation)
Ø Emission
Photon (UV, Blue Light)
Activator
Host
Quantum Efficiency η =number of emitted photons
number of absorbed photons
krad
krad + knonrad
=
White LED Dae-Ryong
Photoluminescence
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White LED Dae-Ryong 32http://bp.snu.ac.kr
Thomas Jüstel’s Group, Philips Research Laboratories Angew. Chem. Int. Ed. (1998).
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Thomas Jüstel’s Group, Philips Research Laboratories Angew. Chem. Int. Ed. (1998).
White LED Dae-Ryong 33http://bp.snu.ac.kr
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White LED Dae-Ryong
Radiative Recombination and Nonradiative Recombination
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Bandgap Energy for Semiconductors
MRS Bulletin (1999)
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Direct Band Gap and Indirect Band Gap
C. KittelIntroduction toSolid State Physics
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N = NΩ(4π/ Ω)è Integrating sphere
MEH-PPV thin film
Friend’s Group, Cambridge University Adv. Mater. (1997).
White LED Dae-Ryong
Measurement of Absolute Quantum Efficiency
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Lb = La(1 - μ)Lc = La(1 - A)(1 - μ)èA = (1 – Lc / La)
Lc + La = (1 - A)(Lb + Pb ) + ηLaAè η = {Pc - (1 - A)Pb} / LaA
L : # of photons in laser regionP : # of photons in PL regionμ : sample absorption of scattered light from sphereA : sample absorption of incident light
Friend’s Group, Cambridge University Adv. Mater. (1997).
White LED Dae-Ryong
Measurement of Absolute Quantum Efficiency
38http://bp.snu.ac.kr
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2S+1LJ
S : total spin quantum number (spin-up : s = +1/2, spin-down : s = –1/2)
L : total orbital quantum number (L = 0,1,2,3,4,5,…. è S,P,D,F,G,H,…)
J : total angular momentum quantum number (J = L +S)
ex) F : 1s22s22p5
S = +1/2
L = 1
J = 3/2, 1/2
∴ F의 Ground State에서의 Term Symbol은 2P3/2
ml
+1 0 -1
ms
White LED Dae-Ryong
Term Symbol
39http://bp.snu.ac.kr
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ml
+3 +2 +1 0 -1 -2 -3
ms
Ex) Eu : [Xe]4f75d06s2
Eu3+ : [Xe]4f6
Eu3+
L=3, S=3
∴ 7F0, 7F1,
7F2, 7F3,
7F4, 7F5,
7F6
ml
+3 +2 +1 0 -1 -2 -3
ms
Eu3+
L=2, S=2
∴ 5D0, 5D1,
5D2, 5D3,
5D4
White LED Dae-Ryong
Term Symbol
40http://bp.snu.ac.kr
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White LED Jongmin
Energy Level Diagrams for Rare-Earth Elements
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4T1t2
e
Mn2+
6A1
t2
eMn2+
Ene
rgy
4G
6S
Crystal-FieldSplitting
4T1
4T2
4A14E
6A1
• Characteristic emission of Mn2+ ions: 4T1 (excited) – 6A1 (ground)
White LED Jongmin
Energy Diagram of Mn2+ Ion (4T1 -6A1 Transition)
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Emission of CePO4
~3.6 eV
Absorption of CePO4
G. Blasse and A. Bril, Philips Research LaboratoriesJ. Chem. Phys. (1969)
254 nm excitation
Electronic Structure of CePO4
White LED Yejun 43http://bp.snu.ac.kr 43http://bp.snu.ac.kr
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White LED Yejun 44http://bp.snu.ac.kr 44http://bp.snu.ac.kr
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Even if the quantum efficiency of a phosphor is over 100%, the energy conversion efficiency is lower than 100%!
Meijerink’s Group, Utrecht University, Netherlands Science (1999).
White LED Dae-Ryong 45http://bp.snu.ac.kr
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Proposed Mechanisms of Quantum Cutting
Meijerink’s Group, Utrecht University, Netherlands Science (1999).
White LED Dae-Ryong
Quantum Cutting (LiGdF4:Eu3+)
46http://bp.snu.ac.kr
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Meijerink’s Group, Utrecht University, Netherlands Science (1999).
White LED Dae-Ryong
Quantum Cutting (LiGdF4:Eu3+)
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Gadolinium -> Europium
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PL Spectra PLE Spectra
Meijerink’s Group, Utrecht University, Netherlands Science (1999).
White LED Dae-Ryong
Quantum Cutting (LiGdF4:Eu3+)
48http://bp.snu.ac.kr
_____________
___________________
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Hyun M. Jang’s Group, Postech Adv. Funct. Mater. (2007).
White LED Dae-Ryong 49http://bp.snu.ac.kr
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Quantum Efficiency
è 104 ~ 117%
è Compared to YBO3:Tb3+
Hyun M. Jang’s Group, Postech Adv. Funct. Mater. (2007).
White LED Dae-Ryong
Quantum Cutting (CaSO4:Tb,Na)
50http://bp.snu.ac.kr
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Hyun M. Jang’s Group, Postech Adv. Funct. Mater. (2007).
White LED Dae-Ryong
Quantum Cutting (CaSO4:Tb,Na)
51http://bp.snu.ac.kr
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C. R. Ronda, Caltech, Interface (2003)Praseodymium
White LED Jongmin
Quantum Splitting Phosphors
52http://bp.snu.ac.kr
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V. I. Klimov, Los Alamos National LaboratoryNature (2004)
White LED Jongmin
Energy-Transfer Pumping of Semiconductor Nanocrystals
53http://bp.snu.ac.kr
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E. Jang, SAIT, Adv. Mater. (2007)
White LED Jongmin
Nanocrystal Applications to LEDs
54http://bp.snu.ac.kr
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K. Nishizuka, Kyoto University Appl. Phys. Lett. (2007)
White LED Jongmin
Indium Composition Variations
55http://bp.snu.ac.kr
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___________
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- Electron-hole pairs excited within the QW couple to electron vibrations at the metal/semiconductor interface when the energies of electron–hole pairs and of the metal SP are similar
A. Scherer, Caltech, Nat. Mater. (2004)
White LED Jongmin
PL Enhancement and Surface Plasmon Dispersion
56http://bp.snu.ac.kr
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A. Scherer, Caltech, Appl. Phys. Lett. (2005)
White LED Jongmin
PL Enhancement and Surface Plasmon Dispersion
57http://bp.snu.ac.kr
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58
Nanophosphors
http://bp.snu.ac.kr
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59
Phosphor
Applications
Electron BeamUV Light
Luminescence
Activator
Host
Luminescent material (phosphor):
A solid which converts certain types of energy into electromagnetic radiation.
Introduction
Nanophosphor Jongmin http://bp.snu.ac.kr
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q Nanophosphor
• Higher packing density
• Lower scattering of light
• Quantum size effect
• Low quantum efficiency, probably due to the
surface adsorbates and defects in nanocrystals.
• PL properties will largely depend on the
thermal histories of nanoparticles.
• However, characterizations of phosphor itself have been rare.
Need to systematically characterize the luminescence properties for developing high-efficiency nanophosphors
q Problems
(S. J. Chua’s group, APL, 1998)
518 nm
460 nm
507 nm
400 450 500 550 600 650 700 750
Wavelength (nm)
PL
inte
nsit
y (a
.u.)
ZnS:Cu
ZnS:Mn
ZnS:Eu
T = 300 K
lex = 325 nm
ZnS nanoparticles (3 nm)
590 nm
Introduction
Nanophosphor Jongmin 60http://bp.snu.ac.kr
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NanocrystalSize
Crystallinity
Capping
Concentration
Modification of Surface state
Nonradiative recombination center
Surface-to-volume ratio
Radiative recombination center
The Factors of PL Enhancement/Retardation
Nanophosphor Jongmin 61http://bp.snu.ac.kr
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62
Non-Uniform Local Strain
Point Defects, Off-Stoichiometry,Stacking Faults, Dislocations, etc.
Distortion of
Lattice
NO STRAIN
Lattice Mismatch between Substance and Thin Films
UNIFORM STRAIN
NON-UNIFORM LOCAL STRAIN
Defect-FreeSingle Crystal
Non-Uniform Distribution of Local Strain
Nanophosphor Jongmin http://bp.snu.ac.kr
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Synthesis and Photoluminescence of MnSynthesis and Photoluminescence of Mn--Doped Doped
Zinc Sulfide NanoparticlesZinc Sulfide Nanoparticles
Synthesis and Photoluminescence of MnSynthesis and Photoluminescence of Mn--Doped Doped
Zinc Sulfide NanoparticlesZinc Sulfide Nanoparticles
Dongyeon Son, Dae-Ryong Jung, Jongmin Kim, Taeho Moon, Chunjoong Kim, and Byungwoo Park*
APL (2007)
63http://bp.snu.ac.kr
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64
How to improve the luminescence properties?What is the optimum condition?
The Goals:
ü Synthesis of nearly monodisperse ZnS:Mn nanoparticleswith a simple method
ü Doping-concentration effectsüAnnealing-temperature effects for
both the water/organic quenching and the local strain
• Nanoparticles with monodispersity:Technical challenge for luminescence applications
• Temperature dependence of ZnS:Mn nanocrystals: In aspect of water/organic quenching and local strain
Motivation
Nanophosphor Dongyeon http://bp.snu.ac.kr
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65
Heating (90°C for 10 h)Cleaning and Drying (60°C for 5 h)
Nearly Uniform-SizedZnS:Mn Nanoparticles (7.3 ± 0.7 nm)
Zn(CH3COO)2 Mn(NO3)2
Mn NitrateZn Acetate
Ethanol
D. I. Water
Sodium Linoleate
Yadong Li’s group, Nature (2005).
(Liquid-Solid-Solution)
CH3CSNH2
Thioacetamide
(C17H31)COONa
Zn2+
S2-
Cubic Zinc Blende (F43m)
ZnS Structure
Synthesis of ZnS:Mn Nanoparticles by LSS Method
Nanophosphor Dongyeon http://bp.snu.ac.kr
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66
• XRD patterns with different Mn concentrations
• Cubic zinc-blende structure, no secondary phases
10 20 30 40 50 60 70
(8%)
(10%)
(2%)
(1%)
(0%)
0.6%
0.5%
0.3%
0.2%
0%
(5%)
cubic zinc blende
1.0%
(20
0) (22
0)
(31
1)
Inte
nsi
ty (
arb
. u
nit
)
Scattering Angle 2q (degree)
(11
1)
* The values in the parentheses are Mn precursor concentration during syntheses.
X-Ray Diffraction for Various Doping Concentrations
Nanophosphor Dongyeon http://bp.snu.ac.kr
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67
• TEM images show nearly monodisperse (7.3 ± 0.7 nm) ZnS:Mn nanoparticles.
• The inset represents diffraction patterns confirming crystalline ZnS.
ZnS (111)
ZnS (111)
(111)
(220)(311)
5 nm5 nm
ZnS
ZnS
Nearly Monodisperse Nanoparticles
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68
300 350 400 450 500
3.60 3.65 3.70 3.75 3.80 3.85
Wavelength (nm)
Ab
sorb
ance
(ar
b.
un
it)
(a
hn)2
(a
rb.
un
it)
Photon Energy (eV)
Fitted Eg: ~3.8 eV(~7 nm ZnS)
• The fitted Eg (~3.8 eV) is larger than that of bulk ZnS (3.7 eV).
• The calculated Eg value by Brus equation: 3.79 eV.
Band Gap Estimation of Nanoparticles
Nanophosphor Dongyeon http://bp.snu.ac.kr
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69
vWith the increasing annealing temperature, the local strain was reduced.
The slope of Dk vs. krepresenting the local strain (Δd/d)
500 550 600
2.4 2.3 2.2 2.1 2.0
lex = 325 nm
600°C
300°C
450°C
150°C
Inte
nsi
ty (
arb
. un
it)
Wavelength (nm)
Photon Energy (eV)
Annealing Temp.(Actual Mn Concent.
@ 1 at. %)Local Strain
NanoparticleSize
Room Temp. 1.18 ± 0.42% 5.7 ± 0.5 nm
150°C 0.91 ± 0.34% 6.3 ± 0.4 nm
300°C 0.76 ± 0.29% 6.9 ± 0.5 nm
450°C 0.53 ± 0.22% 7.2 ± 0.4 nm
600°C Phase Transition Phase Transition
The Effect of Annealing Temperature on PL Properties
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70
Linoleic Acid: (C17H31)COOH Sodium Linoleate: (C17H31)COONa
• TGA result for the ZnS:Mn nanoparticles:evaporation of water (Region A) + decomposition of organics (Region B).
• CHNS results show the presence of carbon and hydrogen quantitatively.
0 100 200 300 400 50088
92
96
100
Region B
Wei
gh
t (%
)
Temperature (°C)
Region ART
450°C
300°C
150°C
150°C
4.6
1.9
4.9
6.64.5
3.0
0.6
14.5
H (at. %)C (at. %)
450°C
300°C
RT
Water
Organic
Reduction of Water/Organics
Nanophosphor Dongyeon http://bp.snu.ac.kr
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71
• The peak shift of Zn 2p peaks:After 450°C annealing, the peaks are close to the values for pure ZnS.
• Broad shoulder peak (~165.5 eV) of S 2p
1048 1044 1024 1020 168 164 160 156
Binding Energy (eV)
Inte
nsi
ty (
arb
. u
nit
)
Zn 2p3/2
Zn 2p1/2
450°C
RT
150°C
300°C
S 2p
450°C
RT
150°C
300°C
Zn2+ Zn2+ S2-
Peak Shift to the Pure ZnS Values
Nanophosphor Dongyeon http://bp.snu.ac.kr
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72
300°C 450°C150°C
Removal of Water + Organic Capping
Improvement of PL Intensity
Enhanced Crystallinity
• Density estimation from TGA at RT 0.82 organics per nm2
7.32 water molecules per nm2C
CC C
CC
C CC == CC C
C CO
O
H
~2.2 nm
CC C
C
Linoleic Acid: (C17H31)COOH
Schematic Figure for the Annealing-Temperature Effect
Nanophosphor Dongyeon http://bp.snu.ac.kr
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HighlyHighly--Luminescent SurfaceLuminescent Surface--Passivated ZnS:Mn Passivated ZnS:Mn
Nanoparticles by a Simple OneNanoparticles by a Simple One--Step SynthesisStep Synthesis
HighlyHighly--Luminescent SurfaceLuminescent Surface--Passivated ZnS:Mn Passivated ZnS:Mn
Nanoparticles by a Simple OneNanoparticles by a Simple One--Step SynthesisStep Synthesis
Dae-Ryong Jung, Dongyeon Son, Jongmin Kim, Chunjoong Kim, and Byungwoo Park*
APL (2008)
73http://bp.snu.ac.kr
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Heating (90°C for 10 h)Cleaning and Drying (60°C for 5 h)
Annealing (450°C for 3 h)
Nearly Uniform-SizedZnS:Mn Nanoparticles (7.5 ± 0.5 nm)
Zn(CH3COO)2 Mn(NO3)2
Mn NitrateZn Acetate
Ethanol
D. I. Water
Sodium Linoleate
Yadong Li’s group, Nature (2005).
(Liquid-Solid-Solution)
CH3CSNH2
Thioacetamide
(C17H31)COONa
LiOH • H2O
Li Hydroxide Monohydrate
My group, Appl. Phys. Lett. (2007).
74
Synthesis of ZnS:Mn Nanoparticles by LSS Method
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Ene
rgy
4G
6S
Crystal-FieldSplitting
6A1
4T1
t2
e
t2
e
Mn2+
Mn2+
4T1
4T2
4A14E
6A1
• Characteristic emission of Mn2+ ions: 4T1 (excited) – 6A1 (ground)
75
Energy Diagram of Mn2+ Ion (4T1 -6A1 Transition)
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• XRD patterns with different Li concentrations (Mn concent. @ 1 at. %)
• Cubic zinc-blende structure, no secondary phases
Zn2+
S2-
Cubic Zinc Blende (F43m)
ZnS Structure
10 20 30 40 50 60 70
0.35% (20%)
0.34% (15%)
0.34% (10%)
0.18% (5%)
0.08% (2%)
0.04% (1%)
0.00% (0%)
Inte
nsi
ty (
arb
. u
nit
)
Scattering Angle 2q (degree)
(20
0)
(22
0)
(31
1)(1
11)
76
X-Ray Diffraction
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Li Concent.(Li-Precursor Concent.)
450°C AnnealingMn Concent. @ 1 at. %
Local StrainNanoparticle
Size
0 at. %(0 at. %)
0.55 ± 0.12% 7.2 ± 0.4 nm
0.04 at. %(1 at. %)
0.66 ± 0.13% 7.4 ± 0.5 nm
0.08 at. %(2 at. %)
0.67 ± 0.19% 7.5 ± 0.5 nm
0.18 at. %(5 at. %)
0.62 ± 0.15% 7.5 ± 0.4 nm
0.34 at. %(10 at. %)
0.62 ± 0.18% 7.6 ± 0.5 nm
0.34 at. %(15 at. %)
0.68 ± 0.19% 7.8 ± 0.6 nm
0.35 at. %(20 at. %)
0.67 ± 0.19% 7.9 ± 0.6 nm
Δk = + kdD
Δd2π
v Scherrer formula
77
Local Strain and Nanoparticle Size
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NanocrystalSize
Crystallinity
Capping
Concentration
Passivation Layer induced by Li
Capping Effects on PL Properties
Nanophosphor Dae-Ryong 78http://bp.snu.ac.kr
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500 550 600
2.4 2.3 2.2 2.1 2.0
0.08%
0.04%
0%
0.18%
0.35%
0.34%
Photon Energy (eV)In
ten
sity
(ar
b. u
nit
)
Wavelength (nm)
0.34%
(2%)
(1%)
(0%)
(5%)
(20%)
(15%)
(10%)
Issue:How to Confirm the Effect ofPassivation Layer?
0.0 0.1 0.2 0.3 0.40
10
20
30
40
h
(%)
Li Concent.
Quantum Efficiency
Li Concent.
η(%
)
79
The Effect of Li Concentration for PL Properties
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• Peak shift in the Li-added samples is attributed to the surface passivation.
(from ZnS to ZnSO4)
• XPS results indicate the formation of zinc-sulfate layer.
• The thickness of passivation layer (ZnSO4) can be estimated from XPS data.
η @ 43%
η @ 33%
η @ 19%1045 1025 1020 172 168 164 160 534 532 530 528 526
1080 1084 1088 1092 718 720 722 724 726205 210 230 235
Kinetic Energy (eV)
ZnSO4
0%
0.34%
0.18%
Binding Energy (eV)
XP
S I
nte
nsi
ty (
arb
. un
it) (a)
Zn 2p
ZnS
ZnSO4
ZnS
0.18%
0.34%
0%
(b) S 2p
ZnO
ZnSO4 0.18%
0.34%
ZnO
0%
O 1s(c)
80
X-Ray Photoemission Spectra
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Without Liη @ 19%
With Li (0.34%)η @ 43%
Amorphous-Layer CoatedZnS:Mn Nanoparticle
ZnS (111)
ZnS (111)
81
TEM Images
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Without Liη @ 19%
With Li (0.34%)η @ 43%
As-synthesized Annealed
H2O (C17H31)COOH
H2O (C17H31)COOH
Li-linoleate(C17H31)COOLi
Passivation accelerated by Li
ZnS
450°C
450°C
ZnSO4
(~1 nm)
ZnS
ZnS ZnS
(7.2 ± 0.4 nm)
(7.6 ± 0.5 nm)
82
Schematic Figure for Li-Addition Effects
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• Clear difference in the PL decay spectra.
• Ratio of the radiative/nonradiative recombination rates.
0 5 10
t = 2.2 ns
t = 3.3 ns
without Li
with Li (0.34%)
PL
In
ten
sity
(a
rb. u
nit
)
Decay Time (ns)
Decay Curves (Time-Resolved PL)
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Without LiWith 0.34 at. % Li
(10 at. % Li precursor)
Quantum efficiency ~19% ~43%
ktotal 4.5 ́ 108 s-1 3.0 ́ 108 s-1
krad 0.9 ́ 108 s-1 1.3 ́ 108 s-1
knonrad 3.6 ́ 108 s-1 1.7 ́ 108 s-1
Single exponential fitting for decay time (t = ktotal
-1)
ktotal = krad + knonrad
η = = krad tkrad + knonrad
krad
• Li-added samples
- Radiative recombination rate
- Nonradiative recombination rate
• ZnSO4 capping layer
- Restriction of nonradiative loss
- The passivation layer activates surface Mn2+ ions.
´
84
Contribution of Radiative/Nonradiative Recombination Rates
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HydroxylHydroxyl--Quenching Effects on the Quenching Effects on the
Photoluminescence Properties of SnOPhotoluminescence Properties of SnO22:Eu:Eu3+ 3+
NanoparticlesNanoparticles
HydroxylHydroxyl--Quenching Effects on the Quenching Effects on the
Photoluminescence Properties of SnOPhotoluminescence Properties of SnO22:Eu:Eu3+ 3+
NanoparticlesNanoparticles
Taeho Moon, Sun-Tae Hwang, Dae-Ryong Jung, Dongyeon Son, Chunjoong Kim, Jongmin Kim,
Myunggoo Kang, and Byungwoo Park*
J. Phys. Chem. C (2007)
85http://bp.snu.ac.kr
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§ Strong drop of PLE intensities for
nanoparticles with water
§ Nonradiative energy transfer to the
O-H vibration states
(Schmechel’s group, JAP, 2001) (Horrocks’ group, Acc. Chem. Res., 1981)
5Dj
7Fj
Eu3+ (O-H)
~1.5 eV~0.4 eV
wh
3=v
2=v
1=v
0=v
)2
1( += vE whħω
8 nm Y2O3:Eu3+
after 3 months with 50% humidity
in water
ħω
Hydroxyl Quenching
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v Synthesis
- Photoluminescence (lex = 325 nm)
- UV Absorption
- XPS
- XRD, FT-IR, TGA
- SnCl4 & EuCl3 (10 mol. %)
in ethylene glycol at 180°C, for 12 h
- Calcination: 700°C - 1000°C, for 3 h, air SnCl4 EuCl3
180°C, 12hAutoclave
Ethylene
Glycol
(C2H6O2)
SnO2:Eu3+ NanoparticlesCalcination
v Characterizations
Experimental Procedure
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• Reddish orange emission increased with the calcination temperature.
• Symmetry of octahedral oxygen sites is not significantly distorted
from 5D0 - 7F2 / 5D0 - 7F1 ratio.
520 540 560 580 600 620
Energy (eV)
lex
= 325 nm
700°C
800°C
900°C
5D
0-7F
2
5D
0-7F
1
Inte
nsi
ty (
arb
. un
it)
Wavelength (nm)
1000°C
2.3 2.2 2.1 2.0
Energy (eV)
900°C
800°C
700°C
1000°C
5D
0-
7F
1
5D
0-
7F
2
PL Spectra vs. Calcination Temperature
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Water Residual solvent + organic
Removal of chemically-bonded OH groups
-Sn-O-Sn-OC2H4OH -Sn-O-Sn-OH -Sn-O-Sn-O
TGA profile
The first derivative of weight
0 200 400 600 800 1000
88
90
92
94
96
98
100
Temperature (°C)
D
eriv
. W
eigh
t (%
/ °C) (b)
(a)
Wei
gh
t (%
)10°C/min
TGA Profile of As-Synthesized SnO2:Eu3+ Nanoparticles
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90
45.9 ± 6.0 nm
33.0 ± 1.7 nm
34.4 ± 3.3 nm
21.4 ± 1.7 nm
• Rutile structures without any second phase.
• Particle sizes and local strains were analyzed from the peak widths.
20 30 40 50 60
700°C
800°C
900°C
1000°C
(002
)
(220
)
(211
)
(210
)
(111
)
(101
)
(110
)
(200
)
Inte
nsi
ty (
arb
. u
nit
)
Scattering Angle 2q (degree)
Crystallinity and Particle Size from XRD Peak Widths
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91
kd
d
Dk
D+=D
p2
20 25 30 35 400.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
900°C
1000°C
800°C
(00
2)
(22
0)
(21
1)
(20
0)
(10
1)
(11
0)
700°C
Dk
(n
m-1)
k (nm-1)
• The variation of non-uniform distribution of local strain with
the calcination temperature is negligible.
- Slope (Δd/d):
non-uniform distribution
of local strain
Local Strain vs. Calcination Temperature
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92
§ Sn peaks are not significantly changed.
§ From O peaks,correlation between OH-/O2- intensity ratiosand PL intensities.
700 800 900 10000.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
OH
- /O2
- In
terg
rate
d I
nte
nsi
ty R
atio
Calcination Temperature (°C)
480 485 490 495 500 526 528 530 532 534 536
O 1s
3d3/2
3d5/2
Sn 3d
1000°C
900°C
800°C
700°C
Inte
nsi
ty (
arb
. un
it)
Binding Energy (eV)
526 528 530 532 534 536
O 1s
OH-
O2-
Inte
nsi
ty (
arb
. u
nit
)
Binding Energy (eV)
Variation of Hydroxyl Groups vs. Calcination Temperature
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93
• Hydroxyl groups still remain, even in samples calcined at 1000°C.
500 1000 1500 2000 2500 3000 3500 4000
Energy (eV)
SnO2
1000°C
water deformation
OH bendingOH stretchingIn
ten
sity
(a
rb. u
nit
)
Wavenumber (cm-1)
0.1 0.2 0.3 0.4
FT-IR Spectrum Showing Existence of Hydroxyl Groups
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94
520 540 560 580 600 620
hydrothermaltreatment 5
D0-
7F
2
5D
0-
7F
1
after
reheatedbefore
Inte
nsi
ty (
arb
. u
nit
)
Wavelength (nm)
480 485 490 495 500 526 528 530 532 534 536
Energy (eV)
before
after
O 1s
reheated3d3/2
3d5/2
Sn 3d
Inte
nsi
ty (
arb
. u
nit
)
Binding Energy (eV)
2.3 2.2 2.1 2.0
Calcination at 1000°C
Hydrothermal treatmentat 140°C
Reheatingat 700°C
PL Measurement
• PL spectra shows ~20% decrease after the hydrothermal treatment
and full recovery after reheating.
• This behavior with XPS confirms the hydroxyl-quenching effect.
XPS
PL
Hydrothermal Treatment
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