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ugent.belumilab.ugent.benb-photonics.ugent.beOptically stimulated detrapping limiting the storage capacity of persistent phosphors

ICDIM 16 Defects in Insulating MaterialsLyon, France July 12 2016Philippe F. Smet Claude Tydtgat, Dirk Poelman, Katrien W. Meertphilippe.smet@ugent.be

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The game changing persistent phosphor: SrAl2O4:Eu,DyVan den Eeckhout K. et al, Materials 3 (2010) 2536-2566Persistent Luminescence in Eu2+-Doped Compounds: A Review

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thermally, mechanically or optically drivenrelease

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Back of the envelope calculationAccessible traps: 10% of recombination centers2% molar doping by Eu in SrAl2O4Alkaline battery: 407 J/g

Optical battery2,45 eV - 2300mJ/ghn

Charging(filling of traps)

Decharging(emptying of traps)

I (cd/m)Time after sunset (h)Thermally driven (uncontrolled) release

DT = 0CDT = -10CDT = -20C

Botterman et al, Optics Express 23 (2015) A868Persistent phosphor SrAl2O4:Eu,Dy in outdoor conditions: saved by the trap distribution

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Botterman et al., Acta Materialia 60 (2012) 5494-5500Mechanoluminescence in BaSi2O2N2:Eu

BaSi2O2N2:EuMechanically driven release

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Kersemans et al, Applied Physics Letters 107 (2015) 234102Fast Reconstruction of a Bounded Ultrasonic Beam using Acoustically induced PiezoluminescenceMechanically driven release: ultrasound detection

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Whatever the application ( ), energy storage capacity is crucial.Where is the bottleneck?

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Charging CaAl2O4:Eu,NdThe trapping probability is very, very high.Afterglow > 72 hours

How can we unite a (relatively) low storage capacitya 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

Setting up the model: keep it simple & local

Eu2+Trap + eEu3+Empty trap

DetrappingClaude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphors

pnr

Boundary conditions for charging and afterglowpe (excitation rate) is smallTwo solutions l1 and l2: two exponentials

Differential equations

Eu2+

trap

pe 0 : Eigenvalues for charging and afterglow are Solution for charging:

chargingafterglow

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Problem #1

Step in charging curve Step for afterglow

Charging| Afterglow| TL analysisSimple system (one Eu site) Sr2MgSi2O7:Eu,Dy

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Charging| Afterglow| TL analysisProblem #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

Reflectedexcitationlight

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 = 200Claude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphorsCharging| Afterglow

and for the influence of the excitation intensity peClaude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphors

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-60C0C

TL

HeatingEmpty all traps

100%

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-60C0C

TL

HeatingEmpty all traps

100%

1%

60%

Thermal barrierfor trapping

OSL (at charging l) is compatible with:

Different initial rise and drop after chargingExponentials for charging and afterglow are differentAbsorption increases during chargingInfluence of excitation intensityCharging behaviour depends on wavelength (via abs) Different trap filling for different wavelengthsThis is worrying/hopeful for applications and requires careful study!

ResourcesFeature issue on Persistent and Photostimulable Phosphors in Optical Materials Express (published)http://tiny.cc/OMEXPPP

Resources & Acknowledgments

Thank you for your attention !(and your feedback)

Presentation can be found at http://www.slideshare.net/pfsmet

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