1 σ(hf, E ) ~ α (hf) = n(E ) σ(hf, E ) I(λ,x) = I (λ)exp{ - α(λ)x}

(1)

Types of OSL

1. Continuous Wave OSL (CW-OSL): the stimulation intensity is kept constant throughout the duration of the experiment, with simultaneous monitoring of the signal.

2. Linearly Modulated OSL (LM-OSL): the stimulation intensity is linearly increased with time, with simultaneous monitoring of the signal.

3. Non-linearly Modulated OSL (NLM-OSL): the stimulation intensity is non-linearly increased (parabolically, hyperbolically, etc) with time, with simultaneous monitoring of the signal.

4. Pulsed OSL (P-OSL): the sample is exposed to stimulation pulses, while monitoring of the signal takes place when stimulation mode is off (NO FILTERS REQUIRED).

I(λ,x) = I

₀

(λ)exp{-α(λ)x}

Lambert Beer Law

α(λ) = absorption coefficient

I(λ,x) = intensity at position x

I

₀

(λ) = incident intensity

Excitation = ionizing radiation

Stimulation = electromagnetic radiation

Valence Band

Conduction Band

BtB

Exciton

formation

DI1

DI2

TI1

TI2

Intraband

α (hf) = n(E

₀

) σ(hf, E

₀

)

α(hf) = absorption coefficient

n(E

₀

) = concentration of traps/defects

σ(hf, E

₀

) = photo-ionization cross section

σ(hf, E

₀

) ~

E

₀

= optical ionization threshold

energy

(2)

Caution

E

₀

= optical ionization threshold energy in OSL

≠

E = activation energy, trap depth in TL

The theory of OSL is not related to the

corresponding TL theory = the trap

depth/activation energy is not considered in the

photo-ionization theory.

Simultaneous thermal and optical

stimulation

 

exp o

total thermal optical o

E p p p s E k T         _ _     

 

0 exp exp exp exp





E E L t n s s t t k T

 

k T

 

         _ _ _  _ _   _ __             

1. Case of CW-OSL

2. Case of LM-OSL

 



₁



_exp

 

2 2

2

m m m m m

q

L L

   



q t

 

t



_





q t

     

t



q t t





 

t



_





σ estimation: fitting of CW-OSL 1

 Fitting parameters

1. b = kinetic order (ranging between 1 and 2) 2. τ = decay lifetime of the OSL component 3. I0 = maximum intensity of the OSL component

Independent variable: time t (s)

φ = instrumental parameter expressed in units of W/cm2  should be converted in units of photons per cm2



(3)

Deco examples: Quartz

0 20 40 60 80 100 100 1000 10000 100000 C3 C2 O S L ( a .u .) Stimulation Time (s) OSL 1 C1 0 20 40 60 80 100 1000 10000 100000 C3 C2 C₁ O S L ( a .u .) Stimulation Time (s) OSL 2

σ estimation: fitting of LM-OSL

 Fitting parameters

1. u_m=stimulation time where the signal gets its maximum value

2. β = kinetic order (ranging between 1 and 2)

3. Im = maximum intensity of the peak Independent variable: Stimulation time u (s)

Total measurement time

Time corresponding

to maximum intensity

Maximum stimulation

intensity in W/cm

2 1 10 100 0 10000 20000 30000 40000 50000 60000 70000 80000 P bgk C₃ C₂ C₁ L M -O S L ( a .u .) Stimulation Time (s) C₁

BaSO

₄

:Eu

(4)

Non-linearly Modulated OSL (NLM-OSL)

Excitation and Luminescence Photon

Energies Used in OSL Dating

Mineral Energy (wavelength) of excitation photons Energy (wavelength) of luminescence photons Quartz (SiO2) 2.2 – 2.4 or2.7eV (510 – 560or470 nm) green-blue 3.35 eV (370 nm) ultraviolet Potassium Feldspar KAlSi3O8 1.4 eV (880 nm) infrared 3.1 eV (400 nm) Violet

(5)

Excitation and Luminescence Photon

Energies Used in OSL Dosimetry

Dosimeter Energy (wavelength) of excitation photons Energy (wavelength) of luminescence photons Quartz (SiO2) Al2O3:C, BeO,

CaF2:N, CaF2:Dy

MgO, BaSO4:Eu,

KBr:Eu 2.2 – 2.4 or2.7eV (510 – 560or470 nm) green-blue 3.35 eV (370 nm) ultraviolet