Inorganic Phosphors For Solid State Inorganic Phosphors For Solid - - PowerPoint PPT Presentation

Inorganic Phosphors For Solid State Inorganic Phosphors For Solid State Lighting Lighting

Ka Wo Ho

Biochemistry Major Chabot College (August 2003 – May 2006) University of California, San Diego Mentor: Mentor: Dr.

• Dr. Gautam

Gautam Gundiah Gundiah Faculty Advisor: Faculty Advisor: Prof. Anthony K.

• Prof. Anthony K. Cheetham

Cheetham Funding Sources: National Science Foundation Funding Sources: National Science Foundation Mitsubishi Chemical Mitsubishi Chemical

Introduction Introduction

• Light emitting diode (LED) based lighting

Light emitting diode (LED) based lighting-

• efficient for white light.

efficient for white light.

• High luminous efficacy without consuming large amount of energy.

High luminous efficacy without consuming large amount of energy.

• White light is composed of blue, green and red colors.

White light is composed of blue, green and red colors.

Blue LED Yellow Phosphor White Light

Available Nowadays

Green Phosphor

Unavailable Nowadays

Blue LED Red Phosphor White Light yttrium yttrium aluminium aluminium garnet (YAG) garnet (YAG)

Strategies to obtain white light

Y3Al5O12: Ce

?????

Goals

• Investigate new red phosphor that could be excited using the blu

Investigate new red phosphor that could be excited using the blue LED e LED-

• Y

Y3

3Al

Al5

5O

O12

12:Ce+Cr

:Ce+Cr

http://www.answers.com

Experimental Procedure for YAG

Grinding Pellet Pelletize Tube Furnace Gas Gas Heating Solid state route: Mix compounds homogenously by grinding. Samples UV Lamp Powder Diffractometer Impure Samples Pure Samples

Photoluminescence Spectrometer

Photoluminescence Measurement

• -- Check the emission of radiation from

excitation by using specific wavelength. X-Ray Diffraction

• -- Check the purity of the samples.

Mortar & Pestle Pelletizer Tube Furnace Powder Diffractometer Photoluminescence Spectrometer

Powder X-Ray Diffraction

2 0 3 0 4 0 5 0 6 0 7 0 5 0 0 0 0 1 0 0 0 0 0 h o 4 (2 )

• The above matched the standard X-ray diffraction pattern of cubic-Y3Al5O12. Optimal

heating temperature was 1500oC for all reactions.

• Impurities of starting materials present when heating temperature was low.

2 theta Intensity

Y3Al5O12: Ce(2%), Cr(2%)- heated at 1500oC for 2 hours.

Experimental Data

Photoluminescence Measurements

Blue LED Blue LED

Ce Ce Ce Ce Ce Ce

No emission

Schematic

Cr Cr Cr Cr

• Int. Emission

Amount of Cr

• Int. Emission

Amount of Ce

The concentration of the Ce increased that caused quenching of the luminescence. (1 ) YAG : Ce (2) YAG: Ce, Cr

400 450 500 550 600 650 700 200 400 600 800 1000

λem=540nm

Intensity (au) Wavelength (nm) Y3Al5O12:Ce

λex=460nm

Graphs for Photoluminescence Measurement Luminescence of YAG doped with Ce

• Optimal excitation of Ce at 460nm
• Emission centered at 540nm
• Matches with standard spectrum

Luminescence studies on YAG doped with different amounts of Ce and Cr

• Ce % ↑, yellow emission ↓
• Cr % ↑, red emission ↑ (upto

10% Cr )

• Ce absorbs blue excitation

and transfers part to Cr

450 500 550 600 650 700 750 800 10 20 30 40 50 60 70

660 680 700 720 740

Intensity (au) Wavelength (nm) 20%, 5% 10%, 2% 2%, 2% Ce, Cr

λex= 460nm

Intensity (au) Wavelength (nm)

Cr emission

• When Ce>20%, no pure

phase obtained.

• When Cr=10%, quenching

Observed.

Summary

• Synthesized pure samples of YAG:Ce+Cr
• Determined that energy transfer occurs between Ce and Cr
• Reduced the Ce emission (540nm) by luminescence quenching
• Increased Cr emission (700nm)

Further work…

• Improve the efficiency of energy transfer (intensity of Cr peak) by attempting

synthesis of Gd3Al5O12:Ce+Cr

• Look for green phosphor that could be excited by blue LED

Material Research Laboratory, UCSB Material Research Laboratory, UCSB

Mentor Mentor:

: Gautam Gautam Gundiah Gundiah

Faculty Advisor Faculty Advisor: Prof. A. K.

: Prof. A. K. Cheetham Cheetham

INSET: Samantha Freeman,

Liu-Yen Kramer, Nick Arnold, Andrew Morrill

CNSI: Prof. Evelyn Hu Cheetham Group: Eduardo Falcao, Kinson Kam, Crystal Merrill,

Russell Feller, Katherine Page, Zeric Hulvey, Ethan Sullivan

Joe Doyle Seshadri Group members, Norman Hoffmann INSET interns

Acknowledgements

Question ???? Thank You for your kind attention! Thank You for your kind attention!

What is LED?

Definition

• GaN-based diodes emit bright violet-blue light, which can be used to

pump longer wavelength phosphors to obtain white light emitting diodes(LEDs).

http://www.treehugger.com

• Blue LED is a GaN-based light

emitting diodes.

• Developed by Prof. Shuji

Nakamura who works in UCSB now.

Application for Blue LEDs?

• Traffic light
• Medical instruments.
• Displays
• Headlight of cars
• TV displays

Advantages for using Blue LEDs?

• Absolutely save more energy than compact fluorescent lamp,

incandescent lamp and high-pressure sodium lamp.

• Save energy, Save money!
• Good color rendering for object.

Materials for YAG

(1)Y3Al5O12 Y2O3 +Al2O3 (2) Y3Al5O12: Ce Y2O3 +Al2O3 +CeO2 (3) Y3Al5O12: Ce, Cr Y2O3 +Al2O3 +CeO2 +Cr2O3

460nm for Blue LED

Crystal-field splitting for Ce3+