Transcript Shockwave Processing of Electroluminescent Materials

5/9/2008
Processing
ZnS based
electroluminescent
precursor powder
mixtures with
TNT
Greg Kennedy and S. Itoh
Outline
• Introduction
• Electroluminescence
• Summary of patent application
– US patent application pub# (20070080327)
– European Union Patent (WO2007043676)
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Investigation of the process
ZnS explosive processing literature
Preliminary experiments
Conclusions and Future Work
Display Technology
EL-11 inch
LCD
3mm $2500
Plasma
Electroluminescence
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Examples of different wavelengths obtained by doping
Electroluminescent material
search
• The research has been financed by companies in a very
competitive and fast growing field
• Most publicly available information is found in patents
and patent applications
• Look at one recent patent and some older published
works
Patent Application Information
US patent application pub# (20070080327)
• Starting Materials
– Primarily ZnS, (Zinc Sulfide)
– Mn and Ir (activators, emission centers)
– Ba and Mg
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Explosive Chamber discussion
Final heat treatment
Gallium Arsenide compound semiconductor
Standard manufacturing of EL element
Explosive Chamber (patent info)
• 0.01mmHg vacuum
(~1Pa)
• 32g TNT selected for
50MPa in one liter
chamber
• TNT is exploded by
heater (4) upon
heating to 450˚C
• ~109g Sample
mixture(8) is placed
under TNT
• Produced “calcined
cake”
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Concerns due to limited
information in the Patent
• Is the explosive separated from the sample?
• Does the TNT detonate by heating?
• Does the TNT melt, boil before detonation?
– How does the vacuum change the detonation process?
– What is heating rate?
• Controls temperature of the powder
• And detonation of TNT
• Maybe electric detonator is ok, but heating of powder might be
necessary for desired final performance
Final Material Processing
(patent info)
Sample B
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Explosive loading
“Calcined cake” is allowed to cool
Washed with deionized water, Dried
Pulverizer/Separator powder (5-20µm)
8 hours Calcining in nitrogen
atmosphere at 700˚C in a silica tube
Washed with glacial acetic acid
– Remove excessive compounds,
flux and impurities
Rinsed with deionized water
Sample C
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Explosive Loading
“Calcined cake” is allowed to cool
Washed with deionized water, Dried
Pulverizer/Separator powder (5-20µm)
• 0.005g GaAs mixed with 15g of
powder in mechanical stirrer
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8 hours Calcining in nitrogen atmosphere at
700˚C in a silica tube
Washed with glacial acetic acid
– Remove excessive compounds, flux
and impurities
Rinsed with deionized water
Increased Luminosity
*Patent application US2007/0080327A1
• Increased from 400 to 4000 cd/m^2
• “The reason for the excellent properties … is
due to instantaneous high temperature, light
emission and/or shock wave produced by the
explosion. However, particulars of the
mechanism for the development of such
favorable properties are still unknown.”
Zinc Sulfide
Phase Change --->
1019˚C
• Sphalerite
• Cubic
• Band Gap
• Wurtzite
• Hexagonal
• Band Gap
3.54eV
3.67eV
High pressure phase change to a different Rock Salt type
structure 15GPa
Mashimo (1999)
Photoluminescence of Zinc Sulfide after
Dynamic Compression
Pure ZnS does not exhibit photoluminescence, but after dynamic
compaction bright photoluminescence occurs due to microdefects
created by shock loading
Phase change from sphalerite to wurtzite
Fluorescence microscopic observation showed blue particles and green
particles
Blue particle concentration can be increased by adding sulphur
The increase in Zn vacancies from the increase in sulphur causes
an increase in photoluminescence intensity
Photoluminscence is reduced after roasting shock loaded sample
*Batsonov, Fizika Goreniya I Vzryva, Vol. 3, No. 3, pp441-448 1967
Shock Assisted Doping
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• Efficient process
– Vacancies and interstitials
• Heterogeneous distribution of defects
• Heterovalent doping is possible
– Eu2+ in NaCl type systems (example)
– Create charge defects
Lapshin and Kurnikova, ZPS, Vol 28. No1, 95-100, Jan. 1978
Explosive Doping
*Lapshin, et. al, ZPS, vol 14, no 6, 1020-1026, June 1971
• Emission bands are shifted to longer wavelengths compared to
thermally processed materials
– Same occurs in thermally produced material after shock loading
• The chemical form of the can change the wavelength
– MnS emission band at
– Mn(NO3)2 demission at
589µm
570µm
• Inhomogeneous phase transformation of cubic and hexagonal
phase generates large number of defects
• Emission bands are wider than thermally produced ZnS:Cu
• Traps are formed, causing long time phosphorescence
Explosive Doping Literature
Zn2SiO4(Mn)
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Pre-shock starting material before firing
8GPa Detonating pressure from tetryl
Fired for 2hrs at 1250oC
The pre-shocked sample had 40% increased
intensity with slight shift to shorter
wavelengths under excitation by 254µm
source
*Horiguchi - Pre-shock Treatment for Preparation of Zn2SiO4(Mn) Phosphor
having High Luminescence Intensity, Naturwissenschaften (1966)
Hypothesis of patent mechanism
• The TNT is heated to 450oC
– Melting point 80.9oC
– Boiling Point 295oC
• Location for Temperature not
described
• TNT
– Melts, then boils
– The boiling tnt mixes with EL
powder
– Vapor evolves and is ignited by
the hot nichrome heater wire
– Localized heating causes
deflagration in the TNT
T1
T2 T3
Experimental Procedure
• Heat the TNT to 450 and test for deflagration or detonation
• Examine mixing of liquid TNT and precursor powder
• Test the powder for exothermic reaction upon heating to
450 (thermal analyzer)
• Duplicate the patent experiment
– Initiation of deflagration by heated wire
– Heating from the base by heater external to the powder container
Heating the TNT
Video of TNT burning
Frame 1
Frame 2
Mixing of TNT and ZnS
• Examine the possibility of mixing of the
TNT and precursor powders
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Nichrome wire heater in plaster
10grams of ZnS
20grams TNT
Glass container
• video
Conclusions
• TNT deflagrates upon heating
– There is no explosion as described in the patent
• Heating the TNT and the powder can lead to
extensive mixing
– This would allow good heat transfer to the
precursor powder and promote localized doping
Future Work
• Using the observations from this work
– Proceed to examine the powder mixture
described in the Chatani Patent
Starting Materials (patent info)
• Sample A -conventional method
• Sample B
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ZnS
MnSO4
ZnO
BaF2
MgCl2
IrCl3
NaCl
100g
0.27g
0.5g
3g
3g
0.012g
2g
• Sample C
– 15g of Sample B after explosive processing and
pulverizing
– 0.005g Gallium Arsenide (1-3µm) compound
Semiconductor
• Mechanical stirrer in plastic bottle (20 minutes)
Comparative Sample A
• 7g ZnSO4 0.5g CuCl 0.5g CuSO4
• 800oC for 40 minutes
• From JP-A No. 2005-126465
Luminance
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Example 1 and 2 ,Measurement is at 280V at 8 KHz
Example 3 voltage was increased to maintain
constant luminance , 315 V after 24hrs, and 330
after 100 hours, stable 120 hours to 1000 hours
EL Element
• Silk screen of sample A, B, C onto BaTiO3
– Greater than 80% of particles 12 to 18µm
• Barium titanate is deposited on the emitting
layer
• Electrode is deposited on the BaTiO3
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