white led · 2018. 1. 30. · 1907 first report on led 1955 gaas led (infrared emission) 1962 first...

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Byungwoo Park

Department of Materials Science and EngineeringSeoul National University

http://bp.snu.ac.kr

White LEDWhite LEDWhite LEDWhite LED

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First Report on Electroluminescence (First LED)

2http://bp.snu.ac.kr

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.

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History of LED


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History of LED (Applications)


Applications of LED

LCD BacklightLCD Backlight

Samsung ElectronicsSamsung Electronics

IlluminationIllumination

ElectimesElectimes

White LEDWhite LED

LEDshopLEDshop

IlluminationIllumination

Lucevista 2007 in SeoulLucevista 2007 in Seoul

5http://bp.snu.ac.krWhite LED BP

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2007. 02

Applications of LED

2007. 02

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Growth Rates


www.research.ibm.com

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Progress in Luminous Efficiency of LEDs


Electron-Hole Recombination of p-n Junction

C. KittelIntroduction toSolid State Physics


Double Heterostructure Injection Laser



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Homojunction and Double Heterojunction


è Confinement of carriers in the active region of double heterostructure (DH).

è High carrier concentration in the active region of DH.

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Double Heterostructure


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Multi Quantum Well Structure


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Structures of InGaN LED


è However, these structures are not practical. - High cost!!

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Trapped Light Problem


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Truncated Inverted Pyramid (TIP) LED


Ecole Polytechnique

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Structures of OLED


White LED Devices

- Nichia High-Power LED- UV LED & RGB Phosphor

White Light

InGaN LED

RGB Light

UV Light

Downconversion(Phosphor)


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


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


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

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Color and Energy


Cones: provide color sensitivity

Rods: color insensitive

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Human Vision


• 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

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Eye Sensitivity Function and Luminous Efficiency


CIE = COMMISSION INTERNATIONALE DE L'ECLAIRAGE = INTERNATIONAL COMMISSION ON ILLUMINATION

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CIE Color Triangle


E. F. ShubertLight Emitting Diodes

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Color Gamut and Color Mixing


Temperature of Sun: ∼6000 K

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Black-Body Radiation


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White LEDs


Phosphor based approaches: color stability

LED-Based Approaches

Phosphor-Based Approaches

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Dichromatic LED


micro.magnet.fsu.edu

InGaN LED (blue) + YAG Phosphor (yellow)

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Phosphor-Based White LED


- 2009-11-17

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.

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Phosphor-Based White LED


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Photon-Recycling Semiconductor LED


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.

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Luminescence


Thomas Jüstel’s Group, Philips Research Laboratories Angew. Chem. Int. Ed. (1998).

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

=

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Photoluminescence


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_________________

___________________________

________________________________________________

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Radiative Recombination and Nonradiative Recombination


Bandgap Energy for Semiconductors

MRS Bulletin (1999)


Direct Band Gap and Indirect Band Gap



N = NΩ(4π/ Ω)è Integrating sphere

MEH-PPV thin film

Friend’s Group, Cambridge University Adv. Mater. (1997).

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Measurement of Absolute Quantum Efficiency


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).

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Measurement of Absolute Quantum Efficiency


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

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Term Symbol


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

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Term Symbol


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Energy Level Diagrams for Rare-Earth Elements


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)

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Energy Diagram of Mn2+ Ion (4T1 -6A1 Transition)


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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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).


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Proposed Mechanisms of Quantum Cutting


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Quantum Cutting (LiGdF4:Eu3+)



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Gadolinium -> Europium

PL Spectra PLE Spectra


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Hyun M. Jang’s Group, Postech Adv. Funct. Mater. (2007).


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Quantum Efficiency

è 104 ~ 117%

è Compared to YBO3:Tb3+


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Quantum Cutting (CaSO4:Tb,Na)



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Quantum Cutting (CaSO4:Tb,Na)


C. R. Ronda, Caltech, Interface (2003)Praseodymium

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Quantum Splitting Phosphors


V. I. Klimov, Los Alamos National LaboratoryNature (2004)

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Energy-Transfer Pumping of Semiconductor Nanocrystals


E. Jang, SAIT, Adv. Mater. (2007)

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Nanocrystal Applications to LEDs


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K. Nishizuka, Kyoto University Appl. Phys. Lett. (2007)

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Indium Composition Variations


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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)

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PL Enhancement and Surface Plasmon Dispersion


A. Scherer, Caltech, Appl. Phys. Lett. (2005)

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PL Enhancement and Surface Plasmon Dispersion


58

Nanophosphors

http://bp.snu.ac.kr

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

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

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

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

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)


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

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


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


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


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


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


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


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


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


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)


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

Nanophosphor Dae-Ryong http://bp.snu.ac.kr

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)


• 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

)


(20

0)

(22

0)

(31

1)(1

11)

76

X-Ray Diffraction


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


NanocrystalSize

Crystallinity

Capping

Concentration

Passivation Layer induced by Li

Capping Effects on PL Properties

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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


• 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


Without Liη @ 19%

With Li (0.34%)η @ 43%

Amorphous-Layer CoatedZnS:Mn Nanoparticle

ZnS (111)

ZnS (111)

81

TEM Images


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


• 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)

Nanophosphor Dae-Ryong 83http://bp.snu.ac.kr

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


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)


§ 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

Nanophosphor Taeho 86http://bp.snu.ac.kr

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


• 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


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


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

)


Crystallinity and Particle Size from XRD Peak Widths

Nanophosphor Taeho http://bp.snu.ac.kr

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


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


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


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


white led · 2018. 1. 30. · 1907 first report on led 1955 gaas led (infrared emission) 1962 first...

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