este2016 detrapping in persistent phosphors
TRANSCRIPT
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Persistent phosphors beyond the afterglow:optical and mechanical detrapping
ESTE2016 – 6th International Conference on Excited States of Transition Elements
Polanica Zdrój, Poland – Augustus 23 2016
Philippe F. SmetClaude Tydtgat, Dirk Poelman, Katrien W. Meert,
Simon Michels, Mathias Kersemans
@pfsmet
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The game changing persistent phosphor: SrAl2O4:Eu,Dy
Van den Eeckhout K. et al, Materials 3 (2010) 2536-2566Persistent Luminescence in Eu2+-Doped Compounds: A Review
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@pfsmet
thermally, mechanicallyor optically drivenrelease
I (cd/m²)
Time after sunset (h)
Thermally driven (uncontrolled) release
DT = 0°CDT = -10°CDT = -20°C
Botterman et al, Optics Express 23 (2015) A868Persistent phosphor SrAl2O4:Eu,Dy in outdoor conditions: saved by the trap distribution
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Back of the envelope calculationAccessible traps: 10% of recombination centers2% molar doping by Eu in SrAl2O4
Alkaline battery: 407 J/g
Charging(filling of traps)
Decharging(emptying of traps)
New persistent phosphors were developed(which are sometimes not even visible to the human eye)
T. Maldiney et al., Nat. Mater. 13, 418–426 (2014), “The in vivo activation of persistent nanophosphors for optical imaging of vascularization, tumours and grafted cells”
Botterman et al., Acta Materialia 60 (2012) 5494-5500Mechanoluminescence in BaSi2O2N2:Eu
BaSi2O2N2:Eu
Mechanically driven release
Whatever the application ( ),
energy storage capacity is crucial.
Where is the bottleneck?
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Charging CaAl2O4:Eu,Nd
The trapping probability is very, very high.
Afterglow
… > 72 hours
How can we unite
• a (relatively) low storage capacity
• a very high trapping efficiency
?
One possible approach:
Modelling trapping and detrapping simultaneously
The experiment... in order to understand (de)trapping
Variation 193K to 353K
Jonas Botterman et al, Physical Review B 90, 085147 (2014)Trapping and detrapping in SrAl2O4:Eu,Dy persistent phosphors: Influence of excitation…
Simple system (one Eu site) – Sr2MgSi2O7:Eu,Dy
Charging | Afterglow | TL analysis
TL cannot be explainedby single trap depth
Setting up the model: keep it simple & local
Eu2+
Trap + e
Eu3+
Empty trap
Detrapping
Claude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphors
pnr
• Boundary conditions for charging and afterglow• pe (excitation rate) is small• Two solutions l1 and l2: two exponentials
Differential equations
Eu2+ trap
• pe 0 : Eigenvalues for charging and afterglow are
• Solution for charging:
charging
afterglow
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Adding distribution for trap depths
Claude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphors
Eu2+ traps
Problem #1
Step in charging curve ≠ Step for afterglow
Charging | Afterglow | TL analysis
Simple system (one Eu site)
Sr2MgSi2O7:Eu,Dy
Charging | Afterglow | TL analysis
Problem #2
Eigenvalues are identical for different pe
≠ Charging dynamics strongly depend on pe
Problem #3
Absorption pe(M-me-m) should decrease<> Absorption increases, depends on pe
Reflectedexcitation
light
Influence of excitation rate pe not negligible, on the contrary!
Large influence, yet pe is lowEffect is proportional to pe x a
OSL : a pe
Claude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphors
Eu2+ traps
It makes sense for charging and decharging…
Emission intensitya = 200
Claude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphors
Charging | Afterglow
… and for the influence of the excitation intensity pe
Claude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphors
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-60°C
0°C
TL
HeatingEmpty all traps
0
10
20
30
-50 -25 0 25 50 75 100
TL in
ten
sity
(ar
b. u
nit
s)Temperature (°C)
100%
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-60°C
0°C
TL
HeatingEmpty all traps
100% 1% 60%
Thermal barrierfor trapping
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-60°C
0°C
TL
HeatingEmpty all traps
100% 1% 60%
OSL (at charging l) is compatible with:
• Different initial rise and drop after charging• Exponentials for charging and afterglow are different• Absorption increases during charging• Influence of excitation intensity• Charging behaviour depends on wavelength (via abs)• Different trap filling for different wavelengths
This is worrying/hopeful for applications…
… and requires careful study!
Part 2: Mechanically driven release
C.-N. Xu et al.
N. Terasaki and C.-N. Xu, IEEE Sens. J., 2013, 13, 3999.
Kersemans et al, Applied Physics Letters 107 (2015) 234102Fast Reconstruction of a Bounded Ultrasonic Beam using Acoustically induced Piezoluminescence
Part 2: Mechanically driven release
BaSi2O2N2:Eu2+
Kersemans et al, Applied Physics Letters 107 (2015) 234102Fast Reconstruction of a Bounded Ultrasonic Beam using Acoustically induced Piezoluminescence
Part 2: Mechanically driven release
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Ultra-sound
Competition with thermal detrapping
Linear response to ultrasound power
Kersemans et al, Applied Physics Letters 107 (2015) 234102Fast Reconstruction of a Bounded Ultrasonic Beam using Acoustically induced Piezoluminescence
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Imaging of US pressure field by Acoustically induced Piezoluminescence
Kersemans et al, Applied Physics Letters 107 (2015) 234102Fast Reconstruction of a Bounded Ultrasonic Beam using Acoustically induced Piezoluminescence
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0
Transducer Increasing distance z (mm)
100 200 300
Kersemans et al, Applied Physics Letters 107 (2015) 234102Fast Reconstruction of a Bounded Ultrasonic Beam using Acoustically induced Piezoluminescence
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Simulation
APL
Fast (10”)
Hydrophone
Slow (10’)
2cm
Towards a fast, full 3D reconstructionof ultrasound beams
Kersemans et al, Applied Physics Letters 107 (2015) 234102Fast Reconstruction of a Bounded Ultrasonic Beam using Acoustically induced Piezoluminescence
Conclusions.
1. In persistent phosphors, optically stimulateddetrapping occurs also at excitation wavelength, limiting the trapping capacity.
2. Mechanoluminescent phosphors can be used tomap ultrasound pressure.
Resources
Feature issue on Persistent and Photostimulable Phosphorsin Optical Materials Express (published March 2016)
http://tiny.cc/OMEXPPP
Chapter
Persistent PhosphorsHandbook on the Physics and Chemistry of Rare EarthsVolume 48, Chapter 274 (2015) 1 - 108
Resources & Acknowledgments
Thank you for your attention !(and your feedback…)
Presentation can be found at http://www.slideshare.net/pfsmet