optical detrapping in persistent phosphors - talk at pre'16

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ugent.belumilab.ugent.benb-photonics.ugent.beOptically stimulated detrapping in persistent phosphors

PRE 16 Photoluminescence in Rare Earths: Photonic Materials and Devices Greenville, SC June 8 2016Philippe F. Smet Claude Tydtgat, Katrien Meert, Jonas Botterman, Katleen Korthout, Koen Van den Eeckhout, Dirk Poelman, Mathias Kersemans, Simon Michels, Jonas J. Joos

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@pfsmet

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Motivation

The disruptive SrAl2O4:Eu,Dy led to many productsVan den Eeckhout K. et al, Materials 3 (2010) 2536-2566Persistent Luminescence in Eu2+-Doped Compounds: A Review

Comparison of afterglow characteristics measured after 10 min exposure to 200 lx of D65 light. A: SrAl2O4:Eu2+, B: SrAl2O4:Eu2+,Dy3+, C: SrAl2O4:Eu2+,Nd3+, D: ZnS:Cu,Co. (Reprinted with permission from [5]. Copyright 1996, The Electrochemical Society). 2

Motivation

I (cd/m)Time after sunset (h)

MotivationIt made us dream about a green, glowing world

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

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


Motivation totally new persistent phosphors were developed(which are sometimes not even visible to the human eye)

T. Maldiney et al., Nat. Mater. 13, 418426 (2014), The in vivo activation of persistent nanophosphors for optical imaging of vascularization, tumours and grafted cells

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Motivation novel applications were realizedKersemans et al, Applied Physics Letters 107 (2015) 234102Fast Reconstruction of a Bounded Ultrasonic Beam using Acoustically induced PiezoluminescenceAcoustically induced PiezoLuminescence (APL)

BaSi2O2N2:Eu

BaSi2O2N2:Eu

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Motivation novel applications were realizedAcoustically induced PiezoLuminescence (APL)

Kersemans et al, Applied Physics Letters 107 (2015) 234102Fast Reconstruction of a Bounded Ultrasonic Beam using Acoustically induced PiezoluminescenceBaSi2O2N2:Eu

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


The experiment... Variation 193K to 353KTrapping and detrapping: the big question

The experiment for SrAl2O4:Eu,Dy...Trapping and detrapping: the big question

ChargingAfterglowTLCannot be fitted withsingle exponentials, at any TBuild-up in signalTrap distribution!Jonas Botterman et al, Physical Review B 90, 085147 (2014)Trapping and detrapping in SrAl2O4:Eu,Dy persistent phosphors: Influence of excitation193K353K

Maximizing trap filling in SrAl2O4:Eu,Dy?Trapping and detrapping: the big question

lexc = 370nmJonas Botterman et al, Physical Review B 90, 085147 (2014)Trapping and detrapping in SrAl2O4:Eu,Dy persistent phosphors: Influence of excitationafterglow

Maximizing trap filling in SrAl2O4:Eu,Dy at low T?Trapping and detrapping: the big question

lexc = 370nmJonas Botterman et al, Physical Review B 90, 085147 (2014)Trapping and detrapping in SrAl2O4:Eu,Dy persistent phosphors: Influence of excitation

Trapping probability is very, very high.Trapping and detrapping: the big question

Charging CaAl2O4:Eu,Nd

Trapping and detrapping: the big questionHow can we unite an (initially) very high trapping efficiency a (relatively) low storage capacity?One possible approach:Modelling trapping AND detrapping simultaneously

Eu2+ + RE3+ < --- > Eu3+ + RE2+Trapping at non-RE defects- strong evidence in e.g. YPO4:Ce,RE -- intrinsic afterglow in SrAl2O4:Eu -Models for Eu2+/Ce3+ doped persistent phosphorsP. Dorenbos, J. Electrochem. Soc. 2005, 152, H107H110 F. Clabau et al.Chem. Mat. 2005, 17, 39043912

LOCALGLOBAL

Modeling trapping and detrappingSetting up the model.

Eu2+Trap + eEu3+Empty trap

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

Modeling trapping and detrapping

pnr

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

Differential equations.

Eu2+

trap

Modeling trapping and detrappingpe 0 : Eigenvalues for charging and afterglow are Solution for charging:

chargingafterglow

Modeling trapping and detrappingSimplified system (one site) Sr2MgSi2O7:Eu,Dy

Charging| Afterglow| TL analysis

Modeling trapping and detrappingAdding distribution for trap depths (no single exp. decay)

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


Problem #1Step in charging curve Step for afterglow


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Modeling trapping and detrappingProblem #2Eigenvalues are identical for different pe Charging dynamics strongly dependent on pe



Problem #3Absorption pe(M-me-m) Absorption increases, depends on pe

Introducing OSL

Influence of excitation rate pe not negligible, on the contrary!

Large influence, yet pe is lowEffect is proportional to pe x a

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

Introducing OSLAbsorption cross-sectionPhosphor particle

Eu2+ (ground state)Electron trap (empty)

Excitationlight


Eu3+Electron trap

Excitationlight



Eu3+Electron trap


Introducing OSLIt makes sense for charging and decharging

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

Introducing OSL

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

Introducing OSLProving OSL(0. All traps emptied)1. Excitation at 0C (2500s)2. Cooling to -60C3. Waiting4. Collecting TL glow curveClaude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphors

Introducing OSLProving OSL(0. All traps emptied)1. Excitation at 0C (2500s)2. Cooling to -60C3. Waiting4. Collecting TL glow curve(0. All traps emptied)1. Cooling to -60C2. Excitation at -60C (2500s)3. Collecting TL curveClaude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphors

Introducing OSLProving OSL(0. All traps emptied)1. Excitation at 0C (2500s)2. Cooling to -60C3. Waiting4. Collecting TL glow curve(0. All traps emptied)1. Cooling to -60C2. Excitation at -60C (2500s)3. Collecting TL curve(0. All traps emptied)1. Excitation at 0C (2500s)2. Cooling to -60C3. Excitation at -60C (2500s)4. Collecting TL curveClaude Tydtgat et al, Optical Materials Express 6 (2016) 844-858Optically stimulated detrapping during charging of persistent phosphors

Introducing OSL

The numbersa = 200, reasonable cross-section compared to Eu2+.Temperature (K)Energy (eV)Shallower trapDeeper traps = 1E14Hzthermal quenching barrierthermal barrier for trapping

ConclusionsOSL (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 for applications and requires careful study!

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

ChapterPersistent PhosphorsHandbook on the Physics and Chemistry of Rare EarthsVolume 48, Chapter 274 (2015) 1 - 108

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Resources & Acknowledgments

Thank you for your attention !(and your feedback)

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

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optical detrapping in persistent phosphors - talk at pre'16

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