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Characterization ofCharacterization ofTPB optical propertiesTPB optical properties

Enrico Nichelatti

UTTMAT-OTT Optical Devices LabENEA – C.R. Casaccia

Rome, Italy

TPB Workshop - MIT 10/19/2012

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Outline

•Hemispheric spectral measurements

•Correction for optically-active samples

•Photoluminescence and photoexcitation spectra

•Results for TPB layers*

*samples prepared at INFN-LNGS (AQ) Italy

TPB Workshop - MIT 10/19/2012

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Hemispheric optical reflectance R and transmittance T(and absorbance A)

incident light

hemisphericreflectance R

hemispherictransmittance T

sample

R + T + A = 1

photoluminescence PL

TPB Workshop - MIT 10/19/2012

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PROBLEM!Measurements of R and T (and A) of an optically-active sample are heavily affected by unwanted Stokes-shifted PL which is excited by the probe beam.

In a typical spectrophotometer, while the impinging probe beam is filtered in wavelength, the reflected (transmitted) beam is detected with no spectral filtering.

Is there a way to “clean” measured photometric spectra of TPB from PL?

TPB Workshop - MIT 10/19/2012

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integrating sphere

TPB

Photoluminescence affects the measurement of R Let us insert a suitable low-pass filter…… no more detected photoluminescence!

Of course, some data elaboration is needed…

TPB Workshop - MIT 10/19/2012

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A suitable low-pass filter is needed…

For TPB, range 2 spans from well below λ = 250 nm (lower measurement limit) up to λ ~ 380 nm. Range 3 is roughly 380 nm < λ < 420 nm.

TPB Workshop - MIT 10/19/2012

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Spectrophotometer Lambda 950PERKIN ELMER UV/VIS/NIR,compatible with optical cryostatcooled at LNT

Spectrofluorometer Fluorolog 3 ISA JOBIN YVON-SPEX Mod.FL3-11 compatible with optical cryostat cooled at LNT

ENEA, C.R. Frascati, V. E. Fermi 45, 00044 Frascati (Rome) Italy, rosa.montereali@enea.it,

http://www.frascati.enea.it/UTAPRAD/lab_mnf.htmTPB Workshop - MIT 10/19/2012

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TPB (167 TPB (167 g/cmg/cm22) over glass slab) over glass slab

VM2000 foilVM2000 foil

280 300 320 340 360 380 400 420 440 4608,0x107

1,2x108

1,6x108

2,0x108

2,4x108

2,8x108

3,2x108

3,6x108

4,0x108

PE

(ar

b. u

nits

)

wavelength (nm)

CAMPIONE_5 (

emi = 422 nm)

(emi

= 445 nm)

300 350 400 450 500 550 6000,0

5,0x104

1,0x105

1,5x105

2,0x105

2,5x105

3,0x105

3,5x105

4,0x105

4,5x105

5,0x105

5,5x105

PL

(a

rb.

un

its)

Wavelength (nm)

specchio VM2000 (

ecc = 295 nm)

(ecc

= 348 nm)

(ecc

= 380 nm)

(ecc

= 400 nm)

300 350 400 450 500 550 6000

1x106

2x106

3x106

4x106

5x106

6x106

7x106

8x106

9x106

PL

(arb

. uni

ts)

Wavelength (nm)

CAMPIONE 5 (15/05/08) % (

ecc = 295 nm)

% (ecc

= 348 nm)

% (ecc

= 380 nm)

PL spectra of the TPB sample (167 µg/cm2) excited at 295 nm, 348 nm and 380 nm.

PLE spectra of the TPB sample (167 µg/cm2) measured at 422 nm and 445 nm.

PL spectra of the VM2000 foil.

TPB Workshop - MIT 10/19/2012

ENEA, C.R. Frascati, maria_aurora.vincenti@enea.it

TPB Worshop - MIT 10/19/2012 9

250 300 350 400 450 500 550 6000,00

0,01

0,02

0,03

0,04

0,05

0,06

Inte

nsity

(m

V)

Wavelength (nm)

Sorgente

Monocromatore di ingresso

Modulo portacampione

Monocromatore di uscita

Controller

PM

Spectrofluorometer equipped with a Xenon lamp

Fluorolog 3 ISA JOBIN YVON-SPEX Mod.FL3-11

Ozone-free Xe lamp (450W) emission spectrum

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Measurement correction (reflectance):

PL

dNRR PLRPERR

S '''4

'''4

~ 2

dNTRTRR PLRPERFR

SFF

PL

0

~

FF

FFS TT

RTRRR

PLFT for constant small PLFT for

filter optical theof ereflectanc and ance transmittspectral : and FF RT

present is PL whererange spectral :PL

ereflectanc sample trueand filter, with measured filter),(without measured as : and ,~

, SRRR

angle soliddetection :R

centres activeoptically ofnumber :RN sections cross PE and PL : and PEPL

low-pass filter requirements

as measured spectrum (without filter)

spectrum with filter placed between sample and detector

evaluation of true sample reflectance

LEGEND

h wavelengtcutoff :0

TPB Workshop - MIT 10/19/2012

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Spectrophotometer and integrating sphere

Perkin-Elmer Lambda 19(dual-beam UV-Vis spectrophotometer)

Perkin-Elmer mod. B013-8277(15 cm diameter integrating sphere)

TPB Workshop - MIT 10/19/2012

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250 300 350 400 450 500 550 6000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

hem

isph

. T &

R

wavelength (nm)

transmittance reflectance

250 300 350 400 450 500 550 6000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

VM2K A

transmittance reflectance interpolation

hem

isph

. T &

R

wavelength (nm)250 300 350 400 450 500 550 600

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

reflectance interpolation

CAMPIONE 1A

hem

isph

. R

wavelength (nm)

УФСУФС22 low-pass filterlow-pass filterVM2000 naked foilVM2000 naked foil TPB (372 TPB (372 g/cmg/cm22))

over VM2000 foilover VM2000 foil

TPB layer over VM2000: null transmittance over all the examined range.High R at λ > 420 nm could be due to TPB or VM2000 or an intermediate situation.Low R at λ < 380 nm, lower than R of VM2000, can be ascribed to low R of TPB itself and high absorbance A of it.

TPB Workshop - MIT 10/19/2012

VM2000 naked foilVM2000 naked foil

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250 300 350 400 450 500 550 6000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

VETRO 2

transmittance reflectance

he

mis

ph

. T &

R

wavelength (nm)

glass slabglass slab

250 300 350 400 450 500 550 6000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

2 F

transmittance reflectance interpolation

he

mis

ph

. T &

R

wavelength (nm)

polystyrene-dilutedpolystyrene-dilutedTPB over glass slabTPB over glass slab

250 300 350 400 450 500 550 6000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

CAMPIONE 4

transmittance reflectance interpolation

he

mis

ph

. T &

R

wavelength (nm)

TPB (356 TPB (356 g/cmg/cm22))over glass slabover glass slab The plots demonstrate that TPB has an

absorption band at about 350 nm (3.54 eV). The further absorption cutoff at λ < 300 nm for the polystyrene-diluted TPB is ascribed to the glass substrate.

250 300 350 400 450 500 550 6000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

POLIVE A

transmittance reflectance

hem

isp

h. T

& R

wavelength (nm)

polystyrene over glasspolystyrene over glass

TPB Workshop - MIT 10/19/2012

TPB Workshop - MIT 10/19/2012

Hemispheric T and R for various TPB surface densities of TPB layer on glass.

Comparison of spectral properties of TPB layers on glass as a function of surface density

Direct T of the glass substrate and of various TPB surface densities (167 -1800 g/cm2) of TPB layer on glass.

TPB overTPB over glass slabglass slab

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Conclusions•An ad hoc procedure has been introduced to optically characterize optically-active samples such as TPB layers.•The procedure allows correcting systematic errors introduced in the hemispheric T and R spectral measurements by (unwanted) photoluminescence.•Results for TPB layers on different substrates, including PL ad PE spectra, have been shown. They confirm that TPB has an absorption band centred at about 350 nm.•Quantitative measurements indicate that UV-VIS reflectance increases with surface density of TPB for samples evaporated on glass in the investigated surface densities range.

TPB Workshop - MIT 10/19/2012

THANK YOU FOR YOUR ATTENTION